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Ronnie Falcao, LM MS, a homebirth midwife in Mountain View, CA

Junk Science about Obesity and Childbearing

I was moved to write this subsection after reading an article that smacks of junk science:  Big Moms, Big Problems - For Obese and Overweight Women, Pregnancy Ups Risks To Selves, Babies By Suz Redfearn [2/22/05]

The author writes, "'Weight is one of the major risk factors for preeclampsia and one of the few things you can do something about," said Schnelle emphatically. "So you have to do everything you can to control it.'"  But Schnelle is not a medical authority; she's a pregnant woman who lost a previous pregnancy to a placental abruption associated with hypertension.  And the author equates hypertension with pre-eclampsia, which is false.  I find it hard to believe that a woman with true pre-eclampsia was just sitting there in a hospital bed waiting for the pregnancy to get to 37 weeks; they would have had that baby out at the first diagnosis of true pre-eclampsia.  My best guess, from the evidence presented in this article, is that Schnelle simply had severe hypertension, which, yes, may be associated with overweight, but that's a far cry from implying that being overweight causes pre-eclampsia and placental abruptions.

Overweight is actually not even listed in my medical texts as a predisposing factor for pre-eclampsia, although I do find some references to an association, which is very different from causation.  Perhaps Redfearn is mistakenly associating the "sudden weight gain" caused by severe edema that is often a symptom of pre-eclampsia.  I did find one study about obesity and pre-eclampsia:

Microarray analysis of differentially expressed genes in placental tissue of pre-eclampsia: up-regulation of obesity-related genes.
Reimer T, Koczan D, Gerber B, Richter D, Thiesen HJ, Friese K.
Mol Hum Reprod. 2002 Jul;8(7):674-80.

Susceptibility genes present in both mother and fetus most likely contribute to the risk of pre-eclampsia. . . . Among those, the obesity-related genes included putative candidate genes associated with the pathogenesis of pre-eclampsia. . . ."

This study implies that the association between obesity and pre-eclampsia is that tendencies may be carried on the same gene.  Losing weight will not cause a woman's genes to change.  In the absence of evidence supporting her assertions, it seems almost cruel to imply that women could have prevented pre-eclampsia by losing weight before becoming pregnant.

Consider these two statements: "More than half of all women age 20 to 39 are overweight or obese" and "In November a British report found that one in three women who die in the United Kingdom during pregnancy, in childbirth or just after labor, is grossly overweight, and that their deaths are often attributable to problems caused by obesity."  Junk science doesn't aim for precision, so there's some sloppiness in the distinction between overweight and obese, but if you take these statements together, then being grossly overweight would actually have a protective effect on pregnant women.

In searching through the UK's hallmark organization, the National Childbirth Trust, and their professional obstetric organization, the Royal College of Obstetricians & Gynaecologists, one finds very little written about obesity in pregnancy.  This seems completely inconsistent with the level of concern one would expect from obesity as a major cause of maternal mortality.  My best guess is that in the UK, as in the US, major causes of maternal mortality are associated with anesthesia accidents and post-cesarean wound infections, which are more serious problems for very obese women than for leaner women.  However, this association is apparently not seen as causative, or we would expect to find something about it in the comprehensive web pages of these two very reputable organizations.  In short, I can't find the British report cited by Redfearn above.  There are some references in the RCOG pages on pre-eclampsia suggesting future directions for research in the area of pre-eclampsia by encouraging pre-pregnant weight loss, but this is speculative.

She cites another study by vague reference, which I'm assuming is this one:

Maternal prepregnancy overweight and obesity and the pattern of labor progression in term nulliparous women.
Vahratian A, Zhang J, Troendle JF, Savitz DA, Siega-Riz AM.
Obstet Gynecol. 2004 Nov;104(5 Pt 1):943-51.

Here's the conclusion from the abstract: "CONCLUSION: Labor progression in overweight and obese women was significantly slower than that of normal-weight women before 6 cm of cervical dilation. Given that nearly one half of women of childbearing age are either overweight or obese, it is critical to consider differences in labor progression by maternal prepregnancy BMI before additional interventions are performed."

What this really says is simply that heavier women progress more slowly, and that this should be taken into account when assessing whether certain stages of labor have gone on for "too long".  This says nothing about the conclusion that Redfearn drew from this study, that heavier women are "thereby incurring a greater risk for cesarean sections."

She is absolutely right that "For overweight women, such operations pose greater risks of life-threatening complications, including blood clots, infection, wound complications and excessive bleeding." which is why the Vahratian study urges caution in recommending additional interventions unnecessarily.

Following the "related articles" from the above PubMed link, on comes to an article about BMI and VBAC success.

The impact of maternal obesity and weight gain on vaginal birth after cesarean section success.
Durnwald CP, Ehrenberg HM, Mercer BM.
Am J Obstet Gynecol. 2004 Sep;191(3):954-7.

"CONCLUSION: Increasing pregravid BMI and weight gain between pregnancies reduce VBAC success after a single low transverse cesarean delivery."

However, there's a very interesting statement just before that one, "However, overweight women who decreased their BMI to normal before the second pregnancy did not significantly improve VBAC success (64.0% vs 58.4%, P = .67)."

Maybe there's something else going on here, and this article is really mis-leading women about the importance of reducing BMI to improve pregnancy outcomes.

Here's another related article:

Intrauterine pressure during the second stage of labor in obese women.
Buhimschi CS, Buhimschi IA, Malinow AM, Weiner CP.
Obstet Gynecol. 2004 Feb;103(2):225-30.

"OBJECTIVE: The perception that obese women have longer labors and a higher frequency of operative delivery because they are "poor pushers" persists despite the absence of objective study. We tested the hypothesis that obese women generate inadequate intrauterine pressure during the second stage of labor."

"CONCLUSION: Obese women produce second-stage intrauterine pressures equivalent to women with a normal BMI, although they may require oxytocin augmentation more often."

Now if you want to see what a relevant article would have been for this topic, take a look at this article:

Pregnancy outcome and prepregnancy body mass index in 2459 glucose-tolerant Danish women.
Jensen DM, Damm P, Sorensen B, Molsted-Pedersen L, Westergaard JG, Ovesen P, Beck-Nielsen H.
Am J Obstet Gynecol. 2003 Jul;189(1):239-44.

OBJECTIVE: This study was undertaken to investigate the relationship between pregnancy outcome and prepregnancy overweight or obesity in women with a normal glucose tolerance test. STUDY DESIGN: A historical cohort study of 2459 pregnant women systematically examined for gestational diabetes was performed. Information of oral glucose tolerance test results and clinical outcome were collected from medical records. RESULTS: The risk of hypertensive complications, cesarean section, induction of labor and macrosomia was significantly increased in both overweight women (body mass index [BMI] 25.0-29.9 kg/m(2)) and obese women (BMI >or= 30.0 kg/m(2)) compared with women who were of normal weight (BMI 18.5-24.9 kg/m(2)). The frequencies of shoulder dystocia, preterm delivery, and infant morbidity other than macrosomia were not significantly associated with maternal BMI. CONCLUSION: Prepregnancy overweight and obesity is associated with adverse pregnancy outcome in glucose-tolerant women.

This tells us that overweight or obesity did not affect outcomes for the baby.  And it's entirely possible that the increased rate of cesarean was because this study was done before the study that recommended greater tolerances for slower labors in larger women.

Here's another related article:

Pregnancy complications and outcomes among overweight and obese nulliparous women.
Baeten JM, Bukusi EA, Lambe M.
Am J Public Health. 2001 Mar;91(3):436-40.

OBJECTIVES: This study examined the associations between prepregnancy weight and the risk of pregnancy complications and adverse outcomes among nulliparous women. METHODS: We conducted a population-based cohort study with 96,801 Washington State birth certificates from 1992 to 1996. Women were categorized by body mass index. Multivariate logistic regression was performed. RESULTS: The rate of occurrence of most of the outcomes increased with increasing body mass index category. Compared with lean women, both overweight and obese women had a significantly increased risk for gestational diabetes, preeclampsia, eclampsia, cesarean delivery, and delivery of a macrosomic infant. CONCLUSIONS: Among nulliparous women, not only prepregnancy obesity but also overweight increases the risk of pregnancy complications and adverse pregnancy outcomes.

Again, the only "morbidity" for the baby was macrosomia, which is, in and of itself, not related with other problems.

You have to look further back for this article:

Prepregnancy weight and the risk of adverse pregnancy outcomes.
Cnattingius S, Bergstrom R, Lipworth L, Kramer MS.
N Engl J Med. 1998 Jan 15;338(3):147-52.

BACKGROUND: Obesity before pregnancy is associated with an increased risk of several adverse outcomes of pregnancy. The risk profiles among lean, normal, or mildly overweight women are not, however, well established. RESULTS: Among nulliparous women, the odds ratios for late fetal death were increased among women with higher body-mass-index values as compared with lean women, as follows: normal women, 2.2 (95 percent confidence interval, 1.2 to 4.1); overweight women, 3.2 (95 percent confidence interval, 1.6 to 6.2); and obese women, 4.3 (95 percent confidence interval, 2.0 to 9.3). Among parous women, only obese women had a significant increase in the risk of late fetal death (odds ratio, 2.0; 95 percent confidence interval, 1.2 to 3.3). Among nulliparous women, the risk of very preterm delivery (at < or =32 weeks' gestation) was significantly increased among obese as compared with lean women (odds ratio, 1.6; 95 percent confidence interval, 1.1 to 2.3), whereas among parous women, the risk was highest among those who were lean. The risk of delivering a small-for-gestational-age infant decreased more with increasing body-mass index among parous than among nulliparous women. CONCLUSIONS: Higher maternal weight before pregnancy increases the risk of late fetal death, although it protects against the delivery of a small-for-gestational-age infant.

It would have been helpful if this study had reported on the probable cause of late fetal death in obese women - diabetes, which is a well-established risk factor for late fetal death.  These were presumably either undiagnosed or poorly controlled diabetics, which speaks to the need for increased vigilance for these women, but this is a manageable problem.

And note that these women were less likely to have low birthweight babies, which is one of the biggest problems in obstetrics today.

Reading all this, one could reasonably conclude that appropriate care for overweight women results in pregnancy outcomes as good or better than leaner women.  It does seem that  morbid obesity is a serious risk factor for some problems, but these are not related to outcomes for the baby, other than cases of undiagnosed diabetes.

Moving along through Redfearn's amazingly inaccurate article, one comes across such gems as "preeclampsia (a possible consequence if gestational diabetes is not properly controlled)".  Pardon me!  That's a wildly speculative statement.

Then we come to the part about how obese women are more likely to have babies with birth defects.

She cites this study:

Maternal obesity and risk for birth defects.
Watkins ML, Rasmussen SA, Honein MA, Botto LD, Moore CA.
Pediatrics. 2003 May;111(5 Part 2):1152-8.

"OBJECTIVE: Several studies have shown an increased risk for neural tube defects associated with prepregnancy maternal obesity. Because few recent studies have examined the relation between maternal prepregnancy obesity and overweight and other birth defects, we explored the relation for several birth defects and compared our findings with those of previous studies."

"CONCLUSIONS: Our study confirmed the previously established association between spina bifida and prepregnancy maternal obesity and found an association for omphalocele, heart defects, and multiple anomalies among infants of obese women. We also found an association between heart defects and multiple anomalies and being overweight before pregnancy. A higher risk for some birth defects is yet another adverse pregnancy outcome associated with maternal obesity. Obesity prevention efforts are needed to increase the number of women who are of healthy weight before pregnancy."

Let's think a minute here.  There's an established association (presumed to be causative) between folic acid deficiency and spina bifida.  There's also a causative relationship between poor nutrition and obesity.  Yet this study fails to present information about folic acid intake or other nutritional deficiencies as possible causative factors of the birth defects, rather than obesity.

This study also ignores the fact that obese women are encouraged to gain less weight during pregnancy than leaner women; in doing so, they end up losing body fat and releasing toxins into their bloodstreams, which is the most plausible reason for an association between maternal prepregnancy obesity and birth defects.  (It would also be interesting to note that women with PCOS (Polycystic Ovarian Syndrome) are likely to be overweight and to have fertility problems.  It is known that babies conceived through fertility treatments are more likely to have birth defects.  This study fails to account for this obvious association.)

Redfearn goes on:  "Other elevated risks to babies attributable to overweight include stillbirth; premature delivery (as a result of preeclampsia); and macrosomia, a condition in which the baby's chest and trunk grow too large to fit easily through the birth canal. Babies with this condition sometimes sustain permanent nerve damage to the shoulders during delivery."

She's making some fantastic leaps of faith here, as most of her conclusions are not supported by the studies I cited earlier.  Yes, undiagnosed diabetes does cause stillbirth, and it is good obstetric care to test obese women for undiagnosed diabetes.  But research doesn't support her implications that maternal obesity causes premature delivery as a result of pre-eclampsia, or that associated macrosomia results in increased nerve damage to the shoulders.  The research cited above explicitly denies these last two adverse outcomes.

Redfearn's article goes on to list numerous associative relationships as if they are causative.  Consider this . . . tall women are more likely to have babies who grow up to be tall people.  Does this surprise you?  Then why would it surprise you that obese women are more likely to have babies who grow up to be obese people?  Without scientific evidence to support the assertion that losing weight will, in and of itself, help their babies to maintain a healthy weight throughout life, it is irresponsible of Redfearn to make these assertions.

Redfearn continues: "As ACOG's president, Dickerson said, she presses obstetricians and gynecologists to counsel patients about weight before pregnancy. 'A doctor wouldn't ignore it if their patient had blood pressure or blood sugar problems,' she said. 'So ignoring a weight issue is not consistent with good medicine.'"  According to the above evidence, the problems in pregnancy associated with obesity are essentially those associated with blood pressure or blood sugar problems, so it makes sense to address those issues whenever encountered, whatever the woman's BMI.

Redfearn's article concludes, "But for the most part, it's up to women to seek out nutrition and exercise guidance to avoid obesity in pregnancy -- and in their offspring."

"''What one weighs going into pregnancy is one of the few things about pregnancy that women can control," said Schnelle, who began her second pregnancy at 220 pounds -- still obese -- but has added only 15 pounds in the following 32 weeks, compared with the 70 pounds she gained in her last pregnancy. 'If your weight isn't controlled, you can face unexpected outcomes, like the tragedy I was hit with. Losing a child because of a disorder that has links to being significantly overweight just shouldn't have happened. It didn't need to happen.'"

Consider this: If Schnelle has gained only 15 pounds in the first 32 weeks of her pregnancy, she has almost certainly lost some body fat during this pregnancy, as the weight of the pregnancy and normal increase in blood volume would exceed 15 pounds by 32 weeks.  In losing that body fat, all of the toxins that were stored in that fat were released into her bloodstream; most of those would have crossed the placenta into her baby's bloodstream.  These toxins are known to be problematic to developing babies, and they might be responsible for causing birth defects in her baby or for triggering a recurrence of hypertension.

But women want to believe that they can guarantee a healthy pregnancy and a healthy baby by losing weight beforehand or by limiting weight gain during pregnancy, even though the latter may actually cause problems, and even though losing weight has never been shown to improve pregnancies or birth outcomes.

In a discussion of Having Faith, a book written about her pregnancy, Sandra Steingraber says, "Being aware of environmental dangers to children's health seemed part of my new responsibility as an expectant mother -- in the same way that infant car-seat recalls and pediatric vaccination schedules were. And yet, oddly, most popular guidebooks on pregnancy encourage mothers-to-be not to dwell too much on environmental dangers that seem to exist outside their individual ability to control."

Here we get to the crux of the matter.  As a society, it is much easier to point our fingers at pregnant women and blame them for problems with their pregnancies or for birth defects in their babies . . . we can tell them that they would not have had any problems if they had only lost weight, gained weight, eaten more protein, taken their prenatal vitamins, etc.

What we, as a society, need to do to support healthier pregnancies and healthier babies is to provide a healthier environment for them, and for all of us.  Once we've accomplished that and are enjoying the healthier pregnancies and healthier babies that will certainly result, then we might be able to fine tune the subtler aspects of healthy pregnancies, such as maternal weight.