Prenatal Weight Gain: Ignoring Possible Harms

We recently started a series discussing again prenatal weight gain politics for "obese" women. 

This was brought on by a press release from a Kaiser study started last year (and publicized in the New York Times, no less) about limiting weight gain in pregnancy for fat women, and by the Institute of Medicine's newly revised guidelines for weight gain during pregnancy earlier this year.

How much weight fat women should gain during pregnancy is a very hot topic in obstetric research currently.  There have been several major studies on the topic already, and there are certain to be many more in the future.  Doctors are salivating at the idea that perhaps the answer to concerns about risks in the pregnancies of women of size could be magically solved by simply limiting weight gain. 

Except the emphasis is going from "obese women should gain LESS weight" to "obese women should gain NO weight" to even "obese women should LOSE weight" during pregnancy...without even having proven the safety of restricted weight gain first.

It's not enough anymore that fat women be kept to far lower weight gains than other women; now the research is taking a disturbingly extremist tone and pushing for NO gain and even weight LOSS, despite the fact that research on limited weight gain already shows some major areas for concern.

As with the Kaiser study, these doctors have already made up their minds about limiting weight gain in fat women, and have decided that this is the message that needs to be pushed to consumers and other doctors.

The problem is that many of these studies have major study design flaws, but almost no one is taking a critical look at the research or asking whether these goals are really safe.  

Let's talk first about the real concerns for harm in weight gain restriction studies.

The Kaiser Study

To review, here are the details about the study from the Kaiser press release on October 21, 2009.

Kaiser Permanente is launching the first clinical trial to help obese women control their weight during pregnancy. The “Healthy Moms” study, funded by a $2.2 million grant from the National Institute of Child Health and Human Development, will begin recruiting this month.

“The goal of the study is to keep obese pregnant women from gaining weight. We believe they can safely maintain their pre-pregnancy weight and deliver healthier babies,” says Kim Vesco, MD, MPH, a practicing OB/GYN and researcher at the Kaiser Permanente Center for Health Research, who will direct the study.

This is the first study to test a weight maintenance program for obese pregnant women, and the first to use weekly support groups as part of the intervention. A small study in Denmark did limit excess weight gain in obese pregnant women, but they still gained an average of 14.5 pounds. Two other larger studies failed to prevent excessive weight gain in obese and overweight pregnant women.

“It may seem counterintuitive to suggest that women control their weight during pregnancy, but these women are already carrying between 50 and 100 extra pounds — and for them any more weight gain could be very dangerous,” said Vic Stevens, PhD, principal investigator who has studied weight loss and weight maintenance for more than 30 years...

The “Healthy Moms” trial will enroll 180 obese pregnant women from Washington and Oregon who are members of the Kaiser Permanente health plan: half will receive one-time dietary and exercise advice; the other half will attend two individual counseling sessions and then weekly group counseling for the remainder of their pregnancy. Women who attend the sessions will be weighed and encouraged to keep and turn in daily food and exercise diaries. Professional weight counselors will facilitate the groups and help motivate the women with behavior change techniques.

The study will follow women throughout their pregnancies to find out how much weight they gain, how large their babies are, and how much weight they retain one year after they give birth. It will also look at birthing complications, the baby’s growth and feeding practices, and whether the mother continues with dietary changes after the baby is born. The study will recruit women for 18 months, and preliminary results are expected in three years.

Remember, the researchers publicized this study before they had even done the research.  This is not objective research, designed to test a hypothesis.  This is Science By Press Release, designed to push a pre-set agenda, even before they have data on its safety.

The title of the NY Times article was "New Goal for the Obese: Zero Gain in Pregnancy." Although the article briefly discusses the controversy over whether gaining no weight is safe, many people will come away from the article with the conclusion that no weight gain is the standard of care and the best goal for "obese" women during pregnancy. 

This is pure public relations marketing in order to push a public health agenda that has actually not yet been proven to be safe or effective.

This is only the first in a plethora of studies to come on little or no weight gain in pregnancy, as bariatrics obstetrics specialists push their agenda of strictly enforced weight gain in fat women.  But can studies like this one really conclusively decide the safety of such an approach?

Let's talk first about the possible harms that could come from strictly limiting weight gain in women of size.

Does The Study Report All Negative Outcomes of Interest?

One major concern is whether these researchers are really going to report all the possible negative outcomes that may be associated with low weight gain, like prematurity, stillbirth, cognitive impairment, or Small-For-Gestational-Age (SGA) and growth-restricted babies. 

In fact, many of these studies on restricting weight gain in "obese" women report only on the outcomes most likely to show benefit with restricted gains (like fewer big babies or cesareans), and have limited or no information about possible harms that can be associated with very low weight gains.  This is cooking the books in favor of a restriction agenda. 

An objective study would look at all the possible benefits and risks from restricting weight gain, and would be large enough and long enough to detect any real risk of harm associated with restricting weight gain.

Yet very few of these restriction studies look at all possible harms, have large-enough sample sizes to detect harm reliably, and have long-term follow-up to detect more subtle harms.

Let's talk about a few of the biggest concerns for harm with restricted gains.

Prematurity

Several of the studies on restricting weight gain in obese women fail to report prematurity rates, yet we know that low weight gains in pregnancy are strongly associated with higher prematurity rates. Yes, the effect is less strong in obese women, but research clearly shows the association is still there.

For example, Shieve found that the magnitude of risk for prematurity with low gain varied by BMI but was still 1.6x for "overweight" women. Nohr also found that low weight gain was associated with an increased risk for preterm birth.

Dietz found an increased rate of very preterm birth with very low weight gain among women of all BMIs.  The effect was strongest in underweight women, but the risk was still more than doubled in "very obese" women.

So prematurity is still a concern with very low weight gains, even in significantly heavy women.  If a restricted gain study does not report on prematurity rates (or does not have sufficient sample size to give it the power to detect a difference in prematurity rates), it is not safe to conclude that low weight gains in obese women is safe or desirable.  Yet these studies often do so.

Stillbirth

Another complication that is almost never examined in these studies is the rate of stillbirth. Because stillbirth is a rare complication, very large data sets are needed to examine the impact of low weight gain on stillbirth, and most of these studies do not have large enough data sets.  So most do not examine the question of stillbirth, yet still routinely conclude that low weight gain is "safe" and results in "better outcomes."

However, one older study that prospectively followed the pregnancies of more than 53,000 women found that "overweight" women had more fetal and neonatal deaths with very low gains (less than 6 lbs.).  They noted:

Even large stores of depot fat do not seem to ensure an optimal outcome of pregnancy when weight gains are very low or mothers lose weight.  Overweight mothers in the lowest weight gain category had perinatal mortality rates twice those of overweight women with somewhat larger gains.

A recent 2009 study confirms the concern about a possible association between very low weight gain and an increased risk for neonatal and infant death, even in "obese" women. 

Clearly, the subject needs more research before a conclusion is reached, but it is vital that this question be examined more closely before the "safety" of restricted gain programs is proclaimed.

The Kaiser press release merely notes that they will "look at" birthing complications. That might include prematurity and stillbirth---but it might not. Instead it may simply be looking at things like shoulder dystocia, cesarean rates, and birth injuries, as many of these studies do, while conveniently ignoring poor outcomes like prematurity or stillbirth.

Neither prematurity nor stillbirth are all that common an occurrence. Is a study sample of 90 women in the intervention group really enough to draw conclusions about prematurity, stillbirth, or the overall safety of a "zero weight gain" policy?

Ketonuria and Cognitive Impairment

In the New York Times article about the Kaiser study, the question of ketones was briefly raised. 

Ketones are produced when the body does not have enough energy for the baby and so it turns to burning fat for its needs. Some research in the past has tied consistent/high levels of ketones in the urine (ketonuria) to impaired cognitive development in the child.

Yet most of these restricted gain studies do not monitor for ketones on a daily or even weekly basis. 

Ketones are usually a sign that the mother's diet is too low in calories and/or carbohydrates for her needs.  If no one monitors for ketones on a frequent basis, the researchers will not know if anyone's diet needs adjusting and those babies will continue to be exposed to large amounts of ketones.  Furthermore, there does not seem to be a plan for any long-term follow-up to see whether cognitive development is normal. 

As noted in the NYT story:

There are concerns. The major one is that women who are not gaining weight will burn fat for energy, producing acidic compounds called ketones, which could be harmful to the fetus. Studies in diabetic women and in animals have found that babies born to women who had more ketones in their blood had lower I.Q. scores than other babies, said Dr. Naomi E. Stotland, an assistant professor of obstetrics, gynecology and reproductive sciences at the University of California, San Francisco.

“What we don’t know is: Are there effects on the babies’ neurological development, or other adverse effects, from women not gaining weight?” Dr. Stotland said. “Some of these women may be losing fat mass, and the question is: Is losing fat mass during pregnancy, when you’re in a higher B.M.I. category, is that safe for the baby?”

Unfortunately, most of these restricted gain studies don't even bother to ask that question by monitoring for ketones or doing long-term follow-up of the babies.

Small for Gestational Age

One very common side effect of too-little prenatal weight gain are infants that are "small for gestational age" (SGA). 

Although the effect of low weight gain is less strong in women of size, the effect is still there. Several studies on weight gain in "obese" women have found that low weight gain is associated with an increased risk of SGA babies, even in very fat women.

For example, the Missouri study of birth certificate data found that while little or no weight gain in "morbidly obese" women resulted in lower rates of pre-eclampsia, large babies, and cesarean sections, it also strongly increased the risk for small-for-gestational-age babies.

The authors shrugged this finding off as unimportant, concluding, "Limited or no weight gain in obese pregnant women has favorable pregnancy outcomes."  Since when is a baby born small for its age a "favorable outcome"?

The study looked at the rates of pre-eclampsia, big babies, cesareans, and SGA and tried to develop "optimal gain" ranges where the risk for all these various adverse outcomes being lowest met.  But they considered a 10% SGA rate acceptable in these tradeoffs.  However, is a 1 in 10 SGA rate really a "favorable" outcome?  That's a lot of too-small babies.

A very large study from Sweden showed similar results.  "Obese" women who gained less than 17 lbs. in pregnancy had lower risks for pre-eclampsia, cesareans, instrumental delivery, and big babies BUT also had 1.68x the risk for an SGA baby (which they conveniently neglected to mention in the study's abstract).  One has to wonder what the risk for SGA would have been with a weight gain close to zero, which is what many of the newest studies are proposing.

A number of other studies have also found that low gestational weight gains are associated with higher rates of SGA babies.  Parker found that "obese" women with very low weight gain more than doubled their risk for SGA babies compared to "obese" women with normal gains by IOM standards.

Edwards found that "obese" women who lost or gained no weight were nearly 3x more likely to deliver SGA infants than those who gained 15-25 lbs.  Of those who lost weight during pregnancy, 11% had SGA infants.  Again, that's a lot of too-small babies at risk for problems.

In addition, Cogswell evaluated data from more than 53,000 women in 8 states and found that "very overweight" women who gained less than 15 lbs. in pregnancy had a 1.5x risk for a low-birthweight baby. 

Recent research suggests that data probably needs to be stratified by class of obesity.  In other words, the risks of SGA with weight loss or very low weight gain in just-barely "obese" women is a lot stronger than the risks of SGA with low gain or small loss in "morbidly" obese women. 

That's a valid point.  The problem is that most doctors do not make this distinction, instead telling most obese women that they need to drastically curtail their weight gain.  And certainly the media message being promoted these days by the Obesity Mafia is that ALL fat women should gain little or no weight in pregnancy....and they are not making distinctions between classes of obesity.  Nor does the Kaiser study seem to be distinguishing between classes of obesity in its study.

The take-home message that most fat women will hear is not to gain any weight in pregnancy....and this could well increase the rate of too-small babies, especially among mid-sized fat women.

However, the fact that the risk for SGA is less strong in "morbidly obese" women doesn't mean that very low weight gains is perfectly safe even in this group either.  It simply means we need more study on the topic to further examine the outcomes in this subgroup. 

Balancing the Risks of Harms vs. Benefits

Weight gain restriction studies trumpet the fact that "obese" women who gain less weight tend to have lower rates of various complications like big babies, pre-eclampsia, and cesareans.  This sounds like a great thing on the surface, but the benefits of those things have to be weighed against the potential for major harm that may come from a premature or SGA baby that results from restricted gains. 

Research shows that low-birthweight babies often face life-long health complications and risks, probably moreso than large babies or babies born by cesarean. Yet these studies routinely place more importance on avoiding large babies and cesareans and discard the finding of increased rates of SGA babies as unimportant.

This is the change in obstetric risk perception that has occurred in maternity care over time.  For many years, in the 1940s-60s, doctors emphasized low weight gains as a way to "prevent" problems like pre-eclampsia. In time it became apparent that the weight gain recommendations were so low that many babies were being born underweight or prematurely. 

In the 1970s and 1980s, a slow reform took place, permitting more weight gain as a way to prevent SGA and premature babies.  The Institute of Medicine weight gain guidelines reflected that.

Now, with the obesity hysteridemic, weight gain in pregnancy is once again under attack.  Some doctors advocate strictly limiting prenatal weight gain for all women, but particularly so for "obese" women.  They see this as the "magic bullet" to prevent pregnancy complications and prevent long-term obesity problems. 

The problem is that the tradeoff means more premature and small-for-gestational-age babies.....a trade-off they find acceptable, but which is questionable, given the really significant long-term health risks of SGA babies. 

Cedergren, author of the 2006 Swedish study mentioned above, echoed this dilemma when she concluded, "What conclusions you draw depends on how you value the adverse effects."  In other words, is a decrease in cesareans and big babies worth an increase in unhealthily-small babies?

I don't believe it is.  SGA and growth-restricted babies face life-long health risks and increased risk for stillbirth; the data is less clear on the effects of macrosomia, with some research suggesting that SGA babies are worse off than LGA babies. 

If I had to choose, I'd rather gain a little more weight and risk a bigger baby than to lose weight or gain almost nothing and risk an unhealthily-small baby, putting it at risk for possible stillbirth or life-long health problems.

But big babies are the ultimate "boogeyman" in the obstetric world these days.  How sad that doctors would rather risk more SGA babies than learn how to deal more effectively with big babies.

Furthermore, these studies do not really prove that restricting weight gain prevents cesareans or pre-eclampsia.  It may simply be a coincidental finding because of study design and iatrogenic issues.  (But that's the topic of the next post!)

But in the meantime, it's important to remember that while many "obese" women gain little in pregnancy and are perfectly fine, some "obese" women gain little and have higher rates of premature babies, SGA babies, and stillbirths. There ARE potential harms that come along with rigid gain-restriction policies.

*Next Up:  Study design limitations of weight-gain restriction studies.