Exercise Your Way to an Easier Pregnancy — Guest Post at What To Expect

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Me, cross country skiing at 8 months pregnant. Super awkward, super fun.

Woohoo! I was asked to guest post for the “Word of Mom” blog at the What To Expect When You’re Expecting website! At the request of a friend, my article was about what the science shows regarding exercise and pregnancy. Here’s a very brief summary of my findings:

  1. Listen your body; it will help you find the right effort level for safe pregnancy exercise.
  2. Women who exercised hard before pregnancy can likely continue to do so during pregnancy without trouble, but competitive athletes should talk to their obstetrician about their pregnancy fitness goals, and may require monitoring.
  3. Even if you weren’t much of an exerciser before pregnancy, there’s no time like the present.
  4. If you’re not a fan of the treadmill or weight room, consider water aerobics or yoga!
  5. It’s a good idea to run your exercise and activity plans by your obstetrician to make sure they’re safe.
  6. If anything unusual or concerning happens during or after a workout, call your OB.

You can read the whole article here on What To Expect.


Cesarean Sections in the U.S. — The Trouble with Assembling Evidence from Data (Guest Blog at Scientific American)

I’ve been invited to guest blog at Scientific American today. The article, which is about the c-section rate in the U.S., was an interesting one for me to write. I initially approached it from the perspective that there were too many c-sections in the U.S., and I wanted to dig around and see whether there was good support for the litigious nature of American society being a causative factor. In the process of my digging, however, I found evidence that changed my thinking. Here’s an excerpt:

While it’s tempting to look at the data and make the assumption that over-medicalization is responsible for the high rate of induction and c-section in the U.S. — and to further extrapolate that the high rate of c-section is responsible for increased maternal mortality — there are several problems with this interpretation. First, it goes without saying that c-sections, while not medically necessary in the majority of deliveries, are lifesaving for both mother and infant when medically required. Per WHO data, those undeveloped nations with the very lowest c-section rates have staggeringly high maternal mortality, with more than 1 in 100 labors resulting in the mother’s death. By comparison, maternal mortality in much of Europe and North America is in the range of 0.001 – 0.03% [3]. This somewhat deromanticizes the image of a native tribeswoman squatting in her hut, giving birth “as nature intended.” It’s easy to forget that if we desire completely natural childbirth, we have to accept the natural maternal and neonatal mortality that accompanies it.

Read more at Scientific American’s guest blog.



More Non-Vax Nonsense

This post is the continuation of last week’s rebuttal of a recent article published on Mothering.com by Jennifer Margulis, entitled “Pregnancy and the Flu Shot.”

Margulis’ article continues with another anecdote (calling to mind a quote I love, often attributed to Roger Brinner, which states: “The plural of anecdote is not data”). This time, the story is about a woman who got the flu shot, and then proceeded to get influenza. No medical intervention or treatment — not ONE — is 100% effective. This is true of all diagnostic techniques, all medications, all vaccinations, all surgeries. In the case of the influenza vaccination, there’s the additional complication that the CDC must make an educated forecast (which Margulis refers to as a “guess,” as though it’s made by throwing dice rather than based upon sound scientific techniques) as to which strains of flu are likely to be most prevalent in a given year. The simple fact is that the CDC doesn’t — can’t — always forecast accurately, but most times they do. Even those years in which the flu shot doesn’t prevent the flu, it attenuates the severity. In the end, deciding to get the flu shot (like so many other decisions) involves doing a risk-to-benefit analysis. The question is, quite simply, do the benefits of getting the shot outweigh the risks.

In order to do a proper risk-to-benefit analysis, it’s important to know both the risks and the benefits. Strong scientific evidence supports that the flu shot is effective in pregnant women (see, for instance, Sumaya et al, Murray et al, Zaman et al). The Sumaya and Zaman studies further examined the efficacy of a maternal influenza vaccination in preventing influenza in newborns. The studies found that, up until about 6 months of age, the infants had influenza antibodies (indicating some degree of immunity, Sumaya et al) and reduced incidence of flu (Zaman et al). One complication in determining the effectiveness of the flu shot is that the vaccine doesn’t prevent non-influenza respiratory illness, and the only way to be sure that a case of illness is influenza is to test for it. As a result, some studies (for instance, Black et al) measure the impact of the influenza vaccine by looking at the rate of medical visits and/or hospitalizations for ANY respiratory illness in vaccinated versus unvaccinated individuals. Studies that don’t measure the effectiveness of the flu vaccine by looking at actual reduction in flu are less likely to show that the vaccine is effective, but to the credit of the researchers, many — including Black and colleagues — admit this shortcoming and weakness of the research. In the end, organizations and researchers who review the scientific literature feel that the shot is effective (that is to say, confers a definite benefit) in pregnant women (see, for instance, Tamma et al, Mak et al, and the recommendations of the CDC).

Then there is the matter of analyzing the risks associated with the influenza vaccine. A large number of scientific studies have shown that routine influenza vaccination is not associated with any severe side effects in individuals who are not allergic to its ingredients (egg, for instance). Pregnant women are not at any greater risk of side effects than non-pregnant individuals, and research suggests no increased risk of pregnancy-related complications (see, for instance, Tamma et al, Munoz et al, Mak et al).

One point in particular made by Margulis is that thimerosal, a mercury-containing preservative in flu vaccinations, causes harm (because mercury is a potent neurotoxin). However, no studies have found any evidence of harm from thimerosal exposure in flu vaccines (see, for instance, Tamma et al). Moreover, a study that looked specifically at neurodevelopment (researchers have wondered if thimerosal could be responsible for increasing the risk of autism and ADHD in infants) found no increased risk of these disorders in thimerosal-exposed infants (Verstraeten et al). Margulis makes the point that the thimerosal studies are weak because they do not include a control group. However, here, she demonstrates her ignorance of the scientific method and of study design. Human experimentation, particularly when it comes to determining whether a substance is dangerous to infants, isn’t ethical. Thimerosal studies aren’t done by injecting some babies (or pregnant women) with thimerosal-containing vaccine and others (the control group that Margulis is looking for) with a vaccine that doesn’t contain the thimerosal. Instead, studies are done by retrospectively (afterward) comparing the health of infants who were exposed to thimerosal to that which is considered normal or expected (“normal” is the control group, even though there isn’t an explicit control in the experimental design). This sort of design is common in medicine and allows ethical determination of toxicity; there is no flaw here.

In the end, while there is good reason to continue to study the effects of thimerosal in vaccines, evidence suggests that in small and occasional doses, it’s not likely to be a problem. Wait, LIKELY? You mean I’m taking a RISK? Yes, you are. You take a risk every time you eat food (it could contain pesticides, mercury, Listeria…), breathe outdoor air in the city (you are breathing pollutants, including benzene and formaldehyde, that cause illness and cancer), enjoy the sunshine (it’s breaking your DNA and possibly causing cancer), or take a tablet of over-the-counter medication (you could be allergic, or could have an adverse reaction). Life is all about risks. There is nothing you do that is without risk. The idea is not to avoid all risk — because that would be impossible — it’s to take MEASURED and APPROPRIATE risks that are WORTH THE BENEFITS. I doubt anyone would argue (at least, not successfully) that you shouldn’t eat, breathe, walk in the sun, or take over-the-counter medication because of the risk. The benefits in each of those cases (and in the case of influenza vaccination) outweigh the risks.

The problem here, as in so much of the anti-vax rhetoric and other harmful nonsense propagated on the Internet and elsewhere in the media, is that Margulis simply isn’t qualified to make judgments on scientific issues. She’s a journalist, according to her byline, and is without a scientific background (possible intro courses in college notwithstanding). As Alice at Science of Mom so beautifully put it in this wonderful guest-post at The Mother Geek, “It would be naïve for me to think that I could understand the vaccine field better than the committees of scientists and doctors who have made this their life’s work.” And that’s coming from a PhD in science! Heck, I’m on that same page; there’s no WAY I would have the hubris to think that I could know better than vaccine scientists whether a vaccine is a good idea, is safe, or confers benefits. That’s why I leave making those decisions to the vaccine scientists. My question, then, is this: if PhDs in science feel it’s important to turn to the TRUE EXPERTS to make vaccination decisions, why doesn’t a journalist? Why don’t the celebrities? Why don’t the moms with great instincts, but no scientific background, who do their vaccination “research” on sketchy Internet sites and by listening to Jenny “Formerly Host of Singled Out” McCarthy instead of by turning to medical experts who’ve made investigating vaccines their life’s work?


Science Bottom Line:* The influenza vaccine is safe and effective in all trimesters of pregnancy, and research supports getting it.


Do you trust the experts? Why or why not?



Black et al. Effectiveness of influenza vaccine during pregnancy in preventing hospitalizations and outpatient visits for respiratory illness in pregnant women and their infants. Am J Perinatol. 2004 Aug;21(6):333-9.

CDC. Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep. 2011 Aug 26;60(33):1128-32.

Mak et al. Influenza vaccination in pregnancy: current evidence and selected national policies. Lancet Infect Dis. 2008 Jan;8(1):44-52.

Munoz et al. Safety of influenza vaccination during pregnancy. Am J Obstet Gynecol. 2005 Apr;192(4):1098-106.

Murray et al. Antibody response to monovalent A/New Jersey/8/76 influenza vaccine in pregnant women. J Clin Microbiol. 1979 Aug;10(2):184-7.

Sumaya et al. Immunization of pregnant women with influenza A/New Jersey/76 virus vaccine: reactogenicity and immunogenicity in mother and infant. J Infect Dis. 1979 Aug;140(2):141-6.

Tamma et al. Safety of influenza vaccination during pregnancy. Am J Obstet Gynecol. 2009 Dec;201(6):547-52. Epub 2009 Oct 21.

Verstraeten et al. Safety of thimerosal-containing vaccines: a two-phased study of computerized health maintenance organization databases. Pediatrics. 2003 Nov;112(5):1039-48.

Zaman et al. Effectiveness of Maternal Influenza Immunization in Mothers and Infants. N Engl J Med. 2008 Oct 9;359(15):1555-64. Epub 2008 Sep 17.

Non-Vax Nonsense

Mothering magazine, once a monthly printed periodical, is now an Internet-only resource for “attachment” or “gentle” methods of parenting (see this great article from Science of Mom that neatly sums up the problems with parenting-style labels). While I’ve occasionally found some useful nuggets among the articles published at Mothering.com, I’m distressed by the complete failure of the editors to acknowledge any of the multitude of scientific studies supporting the benefits and safety of vaccines. In fact, Mothering.com is a bastion of anti-vaccination nonsense, as exemplified by a recent article by Jennifer Margulis, entitled “Pregnancy and the Flu Shot.”

The article is quite long, so this will be Part 1 of a two-part rebuttal. Part 2 is here.

Margulis’ article begins with an anecdotal account of a pregnant woman who was advised by her healthcare practitioner to get a flu shot. Anecdotal accounts — stories, whether fictitious or factual — have no place in scientific decision-making or logical analysis. This is because a single person’s experience may or may not be representative of what usually happens, and there are a number of logical fallacies that can warp our perception of events (see “Why Experience Is Not Evidence.”) In any case, even if we allow the inappropriate use of the anecdote in the flu shot article, it’s completely irrelevant. The pregnant woman in question gets her flu shot, goes on vacation, and within 12 hours, begins to experience flu-like symptoms. “Flu-like” symptoms are caused by many, MANY illnesses, which run the gamut from the common cold to early HIV infection. Thus, citing “flu-like” symptoms is in no way evidence of having the flu. The article goes on to note that the woman felt ill for two and a half weeks, and eventually called her healthcare practitioner, at which point she was diagnosed with bronchitis. The author suggests that the flu shot caused the two-week illness (bronchitis), but this based upon a number of misconceptions.

First, the flu shot simply can’t cause the flu. Why? Because the flu shot contains killed virus (that is to say, not just dead virus, but virus that has been chopped up into little tiny bits). You can no more get “attacked” and sickened by the influenza virus particles in a flu shot than you can get attacked and pecked by the carcass of your chicken dinner. That many people get “flu-like” symptoms after a flu shot is not evidence that the shot causes flu. Flu-like symptoms, which include headache, perhaps mild fever or chills, achiness, and the like, are the result of activation of the immune system. This is the reason they’re shared by so many illnesses; as the immune system revs up to fight off an invading pathogen (an organism that can cause disease), it releases a variety of chemicals, including histamine. The responses to these chemicals assist in the pathogen-fighting process. For instance, the immune system dials up your body temperature, resulting in a fever (and perhaps concomitant headache and achiness). The increased temperature makes it harder for the invading virus or bacteria to reproduce. Further, immune system chemicals that help to call white blood cells to the site of an invasion lead to swelling (such as that which you experience at the site of a vaccination). Bottom line, while not everyone feels flu-like symptoms after a flu shot, many people do, and it means only that the shot is working; it’s causing your immune system to respond and to develop the ability to fight off the flu.

The second problem with the anecdote in Margulis’ article is that it falls victim to the post hoc ergo proctor hoc fallacy, assuming that because the woman in the story got sick after her flu shot, the illness was because of the flu shot. If you get a flu shot and then get in a car accident, win the lottery, or get hit by a meteor, common sense tells you that the second event wasn’t caused by the first, because there is no rational link between the two events. Because the body’s immune system is a complex and (to many people) mysterious thing, it seems rational to connect the event “flu shot” with the subsequent event “illness” in a causal manner. However, no scientist or medical practitioner with an understanding of the immune system would see these events as any more connected than the events in the facetious example of getting a flu shot and winning the lottery.

The Mothering.com article goes on to quote a number of medical practitioners, all of whom recommend (as do the CDC and the American College of Obstetrics and Gynecology) that pregnant women get the flu shot. Reasons include that pregnant women have suppressed immune systems relative to non-pregnant women (which helps to prevent attacking the developing fetus), and that some of the complications of the flu — which include secondary bacterial infection, pneumonia, and dehydration — can be particularly serious to pregnant women and their fetuses.

Margulis then downplays the seriousness of influenza, a common tactic in anti-vaccination rhetoric. Influenza is not, as Margulis claims, “…like a severe cold.” Instead, it’s characterized by extremely rapid onset, high fever, chills, and weakness. One of the problems is that in common parlance, we use “the flu” nonspecifically, and most often in reference to mild, cold-like viral infection. Very rarely is what we call “the flu” actually influenza. Margulis references Dr. Robert Sears, author of The Vaccine Book, who claims that the public has a “misperception” regarding the severity of influenza because the CDC combines influenza deaths with pneumonia deaths for reporting purposes, which makes it impossible to obtain an accurate influenza death toll. Here, both Margulis and Dr. Sears are either confusing or misrepresenting the medicine, however, as pneumonia is a common complication of influenza, and is the complication responsible for most of the influenza-related deaths.

Margulis goes on to state, correctly, that there are very few total cases of influenza resulting in death among pregnant women. I think few healthcare practitioners would argue that the primary reason to get the flu shot is to prevent death, however. Despite the fact that influenza can be fatal, it very rarely is. Still, the complications associated with the flu (dehydration, for instance) have much more serious ramifications in pregnant women. Margulis then cites two physicians (Ayoub and Yazbak) who, after reviewing the literature, published a paper in which they stated that influenza isn’t a threat to a normal pregnancy. However, this paper can’t be taken as any sort of authoritative source, since it was published in the Journal of American Physicians and Surgeons, a publication so questionable and fringe that it isn’t recognized by PubMed (a database of the National Library of Medicine and National Institutes of Health). Articles published in this laughable journal include one asserting that HIV doesn’t cause AIDS, one suggesting that there is a link between abortion and breast cancer, and one that claims global warming is not human-caused, and will actually be beneficial. There is an excellent and complete critique of the organization behind the Journal of American Physicians and Surgeons at the Neurodiversity Weblog, and of the journal itself at Science-Based Medicine.

In contrast to the pseudo-science cited by Margulis, the true scientific literature paints a different picture of the risk of influenza in pregnant women. The CDC points out that not only is influenza more serious in pregnant than in non-pregnant women, it can also cause pregnancy-related complications including preterm labor. A study published in the highly regarded medical journal The Lancet determined that pregnant women appear to be more susceptible to the particularly serious H1N1 (“swine flu”) (Jamieson et al). Another study, again in a very well respected publication, showed that influenza is not uncommon in second- and third-trimester pregnant women, and that while it isn’t transmitted to the fetus, it nevertheless increases the risk of pregnancy-related complications (Reader et al).

Margulis’ article continues with accusation that the influenza vaccine isn’t effective, and, in fact, is dangerous, but the science suggests otherwise. I’ll address these issues in part 2 of this post.


Science Bottom Line:* Influenza is more severe in pregnant women than in non-pregnant women, and pregnant women are more susceptible to influenza that non-pregnant women. Complications associated with influenza during pregnancy extend beyond those normally associated with the flu to include pregnancy-related complications. Influenza presents a serious risk to pregnant women.


Did you get the flu shot while you were pregnant?



Jamieson et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet. 2009 Aug 8;374(9688):451-8. Epub 2009 Jul 28.

Reader et al. Influenza virus infection in the second and third trimesters of pregnancy: a clinical and seroepidemiological study. BJOG. 2000 Oct;107(10):1282-9.

The Autistic Brain

Despite the efforts of researchers and medical practitioners, autism is still only partially understood. Boys are more susceptible than girls by a factor of about four, which may be due to the way that sex hormones interact with a gene called RORA (Sarachana et al), which is one of the many genes implicated in autism (Nguyen et al). Still, the complete genetic profile of autism isn’t known, and it’s clear that environmental factors also affect whether and to what degree an individual with a genetic predisposition expresses autism.

One of the environmental factors cited anecdotally and by some popular media sources as a contributor to autism is the measles, mumps and rubella (MMR) vaccine. However, over 20 scientific studies of vaccines and their side effects (Poland) have shown that there is no link whatsoever.

Interestingly enough, the environmental factors that help to influence development of autism may be prenatal ones, according to a new study in the Journal of the American Medical Association (Courchesne et al). This study examined the size of the brains of young autistic boys, as compared to the size of the brains of young non-autistic boys. With data adjusted for age, the autistic boys had 67% more neurons (brain cells) in an area of the brain called the prefrontal cortex — this part of the brain deals with things like communication and social interaction — than the non-autistic boys had. The autistic boys’ brains were also about 17% heavier than the brains of same-aged non-autistic boys, despite the fact that normally, brains in same-age children don’t vary significantly in weight. Interestingly enough, however, the researchers found that the increased number of neurons was greater than would be suggested by the increased brain weight. This rules out the possibility that autistic children simply have larger brains than non-autistic children, and instead makes it clear that the autistic brain has too many neurons packed into a given space.

What makes this study important in understanding autism is that the neurons of the prefrontal cortex develop and multiply during the prenatal period. Specifically, these neurons develop between approximately the 10th and 20th week of gestation. Once a baby is born, he has all the prefrontal cortex neurons he will ever have. The brain then begins a process that takes place through babyhood and toddlerhood called apoptosis, or programmed cell death. During apoptosis, the brain kills off those neurons that don’t improve brain function or form meaningful connections. This helps the brain to function more efficiently, and is an important part of neural development. The researchers in the Courchesne study did not attempt to determine whether autistic children had more neurons in the prefrontal cortex because they developed more neurons initially, or because their brains failed to perform apoptosis appropriately. Regardless, the study results help to rule out the notion that a single environmental factor or exposure (such as an MMR vaccine) could cause autism. If the prefrontal cortex of autistic children contains more neurons because they overproliferated during the prenatal period, postnatal environmental factors (such as the MMR vaccine) aren’t causative. If the prefrontal cortex contains more neurons because of a failure of apoptosis, postnatal environmental factors could influence the development of autism, but couldn’t cause it to emerge “all of a sudden” (as some parents have described in response to the MMR vaccine), because apoptosis takes place over a long period of time — many years, to be precise.

This study doesn’t fully explain autism — no single study is likely to do so — but it does help move us toward an increased understanding of the disease. Further, by making it clear that autistic brains are physically different than those of non-autistic children, which rules out vaccines as a possible cause of autism, parents can make more accurate risk-to-benefit decisions regarding health care.


What factors do you think researchers will find are implicated in autism?



Courchesne et al. Neuron number and size in prefrontal cortex of children with autism. JAMA. 2011 Nov 9;306(18):2001-10.

Nguyen et al. Global methylation profiling of lymphoblastoid cell lines reveals epigenetic contributions to autism spectrum disorders and a novel autism candidate gene, RORA, whose protein product is reduced in autistic brain. FASEB J. 2010 Aug;24(8):3036-51. Epub 2010 Apr 7.

Poland. MMR Vaccine and Autism: Vaccine Nihilism and Postmodern Science. Mayo Clin Proc. 2011 Sep;86(9):869-71.

Sarachana et al. Sex Hormones in Autism: Androgens and Estrogens Differentially and Reciprocally Regulate RORA, a Novel Candidate Gene for Autism. PLoS One. 2011 Feb 16;6(2):e17116.

Breast Milk and Premature Babies

One of the most fascinating aspects of human breast milk is that the milk literally changes during the course of a nursing relationship. The earliest secretions from the breast — called colostrum — are high in antibodies and protein. Transitional milk comes in a few days post-delivery, and milk changes once again at around two weeks post-delivery. The changes in breast milk occur to meet the changing needs — and changing maturity — of the human infant.

A new study published in the medical journal Pediatrics reports on yet another phase of milk that occurs in the case of a premature delivery (Gabrielli et al). It appears that lactating mothers of premature infants (average age studied was just shy of 28 weeks gestational age) produce milk that is much lower in lactose than the milk produced by mothers of full-term infant.

Lactose is a small sugar molecule made up of two smaller sugar units, called glucose and galactose. To digest lactose, the human intestine uses an enzyme called lactase, which breaks lactose into its separate glucose and galactose components; these are then absorbed into the bloodstream and can be taken up by the cells for energy. While some adults are lactose intolerant, a condition that results from insufficient production of the lactase enzyme, this condition is very, very rare in babies. Premature infants, however, generally don’t digest lactose to the same extent as full-term newborns (see, for instance, MacLean et al, Chiles et al), largely because of reduced lactase activity until the ninth month of gestation (see, for instance, Antonowicz et al, Aurrichio et al, Dahlqvist et al). This reported finding — that breast milk for preemies is especially low in a sugar they find hard to digest — is simply another neat example of human milk conforming to the needs of the human infant, regardless of the circumstances.

Another interesting finding of the study dealt with some pretty technical genetic issues. Stated simply, there are larger sugars than lactose (collectively called oligosaccharides) in human milk, and there are quite a large variety of these larger sugars. While all women produce most of the oligosaccharides, production of some of them requires enzymes that not everyone has. Two different genes (they go by the technical names Le and Se, but we’ll call them Gene 1 and Gene 2 for simplicity’s sake) are involved; women with Gene 1 can make Enzyme 1, and women with Gene 2 can make Enzyme 2. As a result, there are four different types of milk resulting from four different possible gene/enzyme combinations. According to the study, about 70% of women have both genes and produce both enzymes. These women produce the largest number and greatest variety of oligosaccharides. About 20% of the population lacks Gene 1 and therefore lacks Enzyme 1, but has Enzyme 2. About 9% of the population has Gene 1/Enzyme 1, but lacks Gene 2/Enzyme 2. These two groups of women produce fewer total oligosaccharides and a smaller variety of oligosaccharides than women with both genes/enzymes. About 1% of the population lacks both genes, and therefore both enzymes. These women consequently produce the smallest total number and smallest variety of oligosaccharides.

Because oligosaccharides aren’t digested, generally speaking, they don’t contribute to the caloric content or nutritional value of breast milk (Coppa et al). Instead, they pass through the gut and act as soluble fiber, which helps to promote regularity of bowel movements and keep bowel movements soft. They also appear to help prevent pathogenic bacteria from adhering to the gut wall, which helps prevent infection, and they seem to promote the growth of healthy gut bacteria (Bode). Finally, because they pass into the bloodstream to some extent in undigested form (Rudloff et al), it’s hypothesized that they could play a role in immune system function, or act as precursors for a variety of important molecules including some involved in brain function. The milk from mothers of preterm infants appears to be especially high in oligosaccharides, according to the Gabrielli study, which the authors hypothesize is particularly important for these smallest babies. On the basis of their findings, the authors emphasize the importance of human breast milk, ideally from the mother and as opposed to formula, as a source of nutrition for preterm babies.  The authors further note that the differences between women in terms of oligosaccharide production, and the importance of a wide variety of oligosaccharides in milk, justifies the mixing of milk from donors rather than the use of single-donor milk should a baby require breast milk supplementation.


If you’re interested in donating milk, the Human Milk Banking Association of North America needs donations.


Which of human milk’s various properties interests you most?


Antonowicz et al. Development and distribution of lysosomal enzymes and disaccharidases in human fetal intestine. Gastroenterology. 1974 Jul;67(1):51-8.

Aurrichio et al. Intestinal glycosidase activities in the human embryo, fetus, and newborn. Pediatrics. 1965 Jun;35:944-54.

Bode, L. Human milk oligosaccharides: prebiotics and beyond. Nutr Rev. 2009 Nov;67 Suppl 2:S183-91.

Chiles et al. Lactose utilization in the newborn; role of colonic flora. Pediatr Res. 1979; 13:365.

Coppa et al. Characterization of oligo- saccharides in milk and feces of breast-fed infants by high-performance anion- exchange chromatography. Adv Exp Med Biol. 2001;501:307-14.

Dahlqvist et al. Development of the intestinal disaccharidase and alkaline phosphatase activities in the human foetus. Clin Sci. 1966 Jun;30(3):517-28.

Gabrielli et al. Preterm milk oligosaccharides during the first month of lactation. Pediatrics. 2011 Dec;128(6):e1520-31. Epub 2011 Nov 28.

MacLean et al. Lactose malabsorption by premature infants: magnitude and clinical significance. J Pediatr. 1980 Sep;97(3):383-8.

Rudloff et al. Urinary excretion of lactose and oligosaccharides in preterm infants fed human milk or infant formula. Acta Paediatr. 1996 May;85(5):598-603.

The Risks and Benefits of Delayed Cord Clamping

This is the second in a two-part series on umbilical cord-related issues. The first article dealt with cord blood banking.

One of the criticisms that has been leveled against the typical hospital birthing environment is the “assembly line” approach to delivering a baby. In many cases, obstetricians and obstetric nurses have a time frame in which they want to see events take place. It’s been argued that the high Cesarean section rate in the U.S. is among the consequences of this approach. While it’s easy to sit in an armchair and criticize the medical establishment for being too eager to intervene in “normal” deliveries, too quick to augment labor, give medications and episiotomies, and too fast to cut the cord and swoop off with the newborn to measure, bathe, and inoculate, it’s important to remember that there are legitimate medical reasons for many of these interventions (and the speed with which they’re carried out). No, normal birth is not an emergency. However, we live in a very, VERY litigious society, and obstetricians are at exceedingly high risk of being sued. Ever wondered why there aren’t many old obstetricians? It’s not because they burn out or get bored; many truly enjoy their work. It’s because they can be sued by (or on behalf of) each child they deliver until that child turns 18. As such, an obstetrician must continue to carry malpractice insurance for 18 years after the last delivery they attend. Given that malpractice insurance can cost an obstetrician nearly $100,000 a year (a figure impossible to afford when there’s no income to support it), most OBs stop doing deliveries and revert to simple gynecology approximately 20 years before they plan to retire for good. Gives a new perspective on why your OB is quick to intervene, doesn’t it?

In any case, clamping the umbilical cord, which contains the blood vessels that carry oxygen and nutrients from mother to child during pregnancy, is one of the procedures that takes place after delivery. In the case of an emergency — a baby who is born in need of resuscitation, for instance — the cord is clamped immediately so that medical professionals can work freely on the newborn. In the case of a normal, non-emergent delivery, however, there’s been some debate as to when the cord should be cut for the best outcome.

Remember from high school physics that, for each action, there’s an equal and opposite reaction. What this means is that when your baby puts an incredible amount of pressure on your cervix and the tissues of your vagina to stretch them during labor (ouch!), your tissues respond by putting an incredible amount of pressure on your baby in return. Bottom line, your baby gets squeezed — hard — as he or she travels through the birth canal. When a baby who is still connected up to the placenta via an umbilical cord gets squeezed, the result is that blood from the baby literally get squeezed right out the cord and into the placenta.

Imagine, for a moment, a cave-woman giving birth. Once her baby was out, she (or her female attendants) would pick him up and put him to her breast. Cave-mama would cuddle cave-baby and warm him up, and her female attendants would stand around smile and enjoy the beautiful, peaceful scene. Eventually (and this part is speculative, but it’s reasonable and measured speculation), someone would tear the cord (probably using a sharp rock). It’s possible to imagine a similar scenario in, say, pre-Industrial England (but without the cave, and with a scissors instead of a rock). Bottom line, before birthing took place in a hospital, there would have been a natural time gap between the birth of a baby and the returning of the attendants’ attention to the matter at hand (namely, the afterbirth). During this time gap, the baby’s heartbeat would have continued to circulate blood throughout the baby’s body, the umbilical cord, and the placenta. Over the course of several minutes, the quantity of blood in the baby — while low immediately after birth — would have returned to normal. Several minutes later, post-delivery changes in circulation would cause the vessels in the cord to clamp down, naturally sealing the baby off from the placenta and keeping the baby’s blood entirely within its body. At this point, the cord would stop pulsing. A baby allowed to remain attached to the cord until it stops pulsing on its own ends up with a much higher red blood cell count than one who is immediately disconnected; this improves iron status (red blood cells need iron to function), and reduces the need for dietary iron early in life. In fact, breast milk may be low in iron (see an excellent article at Science of Mom on this topic) simply because babies who don’t have their cords cut early don’t need supplemental dietary iron early in life.

Because immediate cord clamping doesn’t allow blood volume in the baby to return to normal, it increases the risk of low neonatal hemoglobin (a marker of too few red blood cells, which can impair oxygen delivery, and leads to increased risk of anemia later in the first year of life). This is associated with a number of potential negative outcomes, including delayed development. Many studies have examined the benefits associated with delaying cord clamping, as opposed to clamping the cord immediately (see, for example, Andersson et al, Ceriani Cernadas et al, Hutton et al, Ultee et al). The studies indicate that the best time to clamp the cord so as to avoid the risk of low neonatal hemoglobin is at approximately three minutes post-delivery.

On the other hand, there’s been speculation (and there’s a small amount of evidence) of risks associated with delayed cord clamping. For instance, Prendiville et al found that delayed clamping can increase the risk of polycythemia (too many red blood cells, proportionally speaking) and hyperbilirubinemia (too much bilirubin, a breakdown product of red blood cells, which leads to jaundice). However, these results haven’t been reproduced in the vast majority of delayed cord clamping studies. Andersson et al, Ceriani Cernades et al, and Ultee et al found no significant increased risk of negative outcome (jaundice or otherwise) with delayed cord clamping (at three minutes post-delivery in each study). Hutton et al found an increased risk of polycythemia in infants whose cords had been clamped at least two minutes post-delivery, but also found that the condition was not associated with any negative outcomes. There is an unpublished study (Mc Donald, PhD thesis) that suggests very delayed cord clamping (5 minutes or longer post-delivery, or when the cord stops pulsing) may increase the risk of jaundice requiring light therapy. While these results have not been replicated elsewhere, it’s probably worth being cautious with extremely delayed cord clamping.

Somewhat delayed cord clamping also appears to benefit premature and low birth-weight babies, though very premature babies are generally born under medically urgent circumstances, and delaying clamping by several minutes is not likely to be feasible. The aforementioned Ultee study focused on slightly premature infants (delivered between 34 and 36 weeks), and showed higher hemoglobin with a three-minute delay. A study of very premature infants (around 28-29 weeks gestational age) found that delaying clamping as much as 30-45 seconds post-delivery as opposed to clamping immediately helped to reduce the otherwise significant risks of late-onset sepsis (infection) and intraventricular hemorrhage (bleeding in the brain) (Mercer et al). The Mercer study didn’t examine the effects of waiting longer than 30-45 seconds, simply because of the emergent nature of extremely preterm births. The authors pointed out that, of course, many very preterm babies would require immediate care, precluding the possibility of waiting even 30 seconds to clamp the cord, but recommend on the basis of their findings that, whenever possible, clamping be delayed a bit. A similar study by Rabe et al found that premature babies in the range of 29-33 weeks gestational age generally had good outcomes when cord clamping was delayed by 45 seconds, despite the delay, and benefited from the delay in terms of reduced need for transfusion.


Science Bottom Line:* If there’s no medical emergency that requires separating baby from mother immediately, the evidence supports waiting three minutes to cut the cord. During this time, the baby should be at the level of the mother (ideally on her chest) to ensure that gravity neither prevents nor inappropriately augments the return of blood into the baby.
Are you in favor of delayed cord clamping?



Andersson et al. Effect of delayed versus early umbilical cord clamping on neonatal outcomes and iron status at 4 months: a randomised controlled trial. BMJ. 2011 Nov 15;343:d7157. doi: 10.1136/bmj.d7157.

Ceriani Cernades et al. The Effect of Timing of Cord Clamping on Neonatal Venous Hematocrit Values and Clinical Outcome at Term: A Randomized, Controlled Trial.  Pediatrics. 2006 Apr;117(4):e779-86. Epub 2006 Mar 27.

Hutton et al. Late vs Early Clamping of the Umbilical Cord in Full-term Neonates. JAMA. 2007 Mar 21;297(11):1241-52.

Mercer et al. Delayed Cord Clamping in Very Preterm Infants Reduces the Incidence of Intraventricular Hemorrhage and Late-Onset Sepsis: A Randomized, Controlled Trial. Pediatrics. 2006 Apr;117(4):1235-42.

Prendiville et al. Care during the third stage of labour. In: Chalmers I, Enkin M, Keirse MJNC editor(s). Effective care in pregnancy and childbirth. Oxford: Oxford University Press; 1989:1145–69.

Rabe et al. A randomised controlled trial of delayed cord clamping in very low birth weight preterm infants. Eur J Pediatr. 2000 Oct;159(10):775-7.

Ultee et al. Delayed cord clamping in preterm infants delivered at 34 36 weeks’ gestation: a randomised controlled trial. Arch Dis Child Fetal Neonatal Ed. 2008 Jan;93(1):F20-3. Epub 2007 Feb 16.

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