Weighing In on Pregnancy Weight Gain
How much weight should you gain when you’re pregnant?
While a cursory glance at the internet may appear to provide a consistent answer, a deeper search risks poking a hornet’s nest of dissonant opinions. There are many ways of thinking about this question. And they fly in wildly different directions.
One approach you’ve probably encountered is that your pre-pregnancy weight determines how much you need to gain, with the idea that people who begin pregnancy underweight need to gain more, and people who begin pregnancy overweight need to gain less. This is a very common approach.
A slightly more nuanced, yet similar take, refers to your “BMI” or ‘body mass index’ as a baseline. This system is meant to account for more diversity among people who are naturally larger or smaller, since factors like height and bones have significant bearings on body weight. The usual recommendation is to gain 25 - 35 lbs if you begin pregnancy with an average BMI. Like the previous practice, it relies on the pre-pregnant body as a baseline to determine the so-called appropriate amount of weight gain
Perhaps you’ve found a breakdown of all the parts of your body that involve weight gain. Although different sources estimate these components in a variety of ways, there is always some overlap. These lists might include the weight of components such as:
The baby (or babies)
The placenta
The amniotic fluid
The uterus
The additional blood volume
The reserve of fat required for making milk
Breast tissue
And others
This is certainly one way of understanding how weight gain during pregnancy is distributed, although I would propose it’s more focused on counting beans than appreciating the big picture.
One thing all these approaches share in common is that their assumptions are far from fixed. How much weight gain is appropriate during pregnancy is a moving target which has changed a lot over time. If you ask your mother or grandmother about recommended weight gain during their own gravidity, there’s a good chance they will have received entirely different information. My own grandmother tells me her pregnancy weight gain was strictly limited and she was advised to eat mostly steamed celery and strained cottage cheese. My mother was told to choose cigarettes over snacks.
Different countries, too, have different ideas about how much weight is best. None of these recommendations are global. In fact, according to the World Health Organization, only about two thirds of the world’s countries have recommendations about weight gain during pregnancy at all. Your own family’s traditions might contrast sharply with your doctor’s or midwife’s recommendations.
So why do we dwell on this? Why do we insist on tracking weight gain, or talking about it at all? What do these recommendations actually mean? How are these numbers determined?
The first and most compelling reason is that many studies have noted an association between maternal weight and birth outcome. People who gain very little weight tend to have smaller babies. Low birth weight is associated with a number of health challenges such as delays in meeting milestones. People who gain large amounts of weight have an increased risk of caesarean birth, and a higher likelihood of certain complications including high blood pressure, gestational diabetes, and large-for-dates babies. These links are what we often see referenced when we read about the importance of monitoring one’s weight during pregnancy.
Most studies track groups of womens’ weight during pregnancy, divide subjects into groups based on weight gain, and note differences in outcomes between the groups. Usually, an association is clear between low maternal weight gain and low infant birth weight, and between high maternal weight gain and large-for-dates babies. This, of course, is a cause for concern, and leads to many recommendations about target weights.
Obviously, there is a correlation between maternal weight gain and infant outcome. But does this necessarily mean the former causes the latter? Or is it possible there are other ways of reading the data?
If we think about it, in some ways the association seems obvious– that how much weight we gain might be related to how big our babies are. When we track weight gain alongside baby size, how can we tell which is the cause, and which is the result? If the baby is naturally large perhaps the maternal body needs to gain the conforming amount of weight to support the optimal growth of that sized baby. We know we can’t make ourselves taller by eating more, or shorter by eating less. The baby’s size is determined by factors other than just how much the pregnant parent eats. Perhaps the more-than-average weight gain didn’t create the big baby, but was a direct result of nurturing a baby of that size. Restricting calories might cause that baby to be smaller, but would this necessarily be in the baby’s best interest? Or is there a possible risk of underfeeding that baby for its naturally large size?
There are several concerning medical conditions also linked to above-average weight gain, including gestational diabetes, macrosomia, and childhood obesity. But again, it is hard to tell from the studies whether maternal weight is actually a cause, a correlation, or even a symptom. Neutralising a symptom does not necessarily cure a condition. For example, if a medical condition related to bone density were causing above-average weight gain, reducing maternal calories would be unlikely to solve the problem. Similarly, even though there is a statistical link between maternal obesity during pregnancy and childhood obesity for the offspring, no studies have ever shown that limiting weight gain during pregnancy is an antidote. Possibly the household’s eating and lifestyle habits, the nutrition modelling within the family, and the genetic profile, could all be just as likely suspects. What we might be seeing here are concurring symptoms, rather than cause and effect.
Another consideration you might encounter in your research is that women’s bodies are all different, for reasons ranging from lifestyle to genetics. The number on the scale does not account for height, muscle mass, or individual structure. Using averages as ideals runs the risk of pathologizing people who fall outside the standard range, but are nonetheless perfectly healthy. There is nothing inherently harmful about being of a smaller or larger build. People’s weight can be affected by many variables, both before and during pregnancy. Even the concept of a BMI (body mass index) doesn’t hold up under scrutiny, as we can see explained here, here, and here. This slightly undermines the basic assumptions of many of the studies, and greatly confuses the generic advice around weight gain.
Another dissonant variable is that not all weight gain is equal. Being a so-called healthy weight is not at all the same as being healthy. The specific foods we eat have a huge impact on the development of the baby, far more so than how much we eat. A pregnant person can gain exactly the recommended number of kilograms by eating twinkies and pringles, or can gain a more individual amount of weight eating nutritious, whole foods. Quality is profoundly more significant here than quantity. All calories are not equal. The over-emphasis on weight gain obscures this vital distinction.
A related issue is that the baby needs specific nutrients, and sometimes we have to eat a lot of a particular category of food for the baby to get enough of it. The baby is not counting calories so much as favouring specific vitamins, minerals, nutrients, and growth factors. If we are craving steak, our baby might be needing more protein, which trumps any concerns about a number on the scale.
Weight gain, after all, is not a simple thing.
A quick glance at the overwhelming industry of diet pills, diet books, diet clubs, courses, programs, doctors, and articles also reveals that controlling one’s weight can be a tricky business. It is not a simple formula of energy in versus energy out. There are too many known variables to name, more that are suspected, and probably more not yet discovered. For example, there are enormous and highly complex psychological factors relating to food such as comfort or distraction, there are cultural impetuses such as finishing everything on your plate or not wasting food, there are genetic predispositions, and there are associated influences such as gut health, inflammation, stress, trauma, age, and hormones. There are also smaller yet cumulative influences such as what time of day you eat, how long you fast between meals or overnight, how deeply you sleep, the order in which you eat specific foods, and how hydrated you are. There is nothing simple about it.
And of course there’s exercise. Physical activity. We all know that one, but it does not often get factored into the studies on weight. Since both maternal and foetal health are linked to physical activity in many ways, including how much rich oxygen and endorphins the baby gets through maternal exertion, one can wonder if the studies on infant outcomes and weight are inadvertently capturing a different synchronicity altogether: the relationship between maternal exercise and infant health. Maybe the weight gain we measure is actually a by-product of the level of fitness, and we’re focusing on entirely the wrong thing. After all, even placental health is improved through cardiovascular exercise during pregnancy. Perhaps the difference in weight we keep measuring is actually just an indicator that keeps distracting us from the real phenomenon: fitness. It would be like concluding that umbrellas cause rain.
Another element underlying this topic, of course, is the over-emphasis on women’s bodies in general, and women’s body shape and weight in particular. It is difficult to disentangle the social biases from any kind of neutral health information. The appearance and presentation of womens’ bodies has been policed and scrutinised, objectified, measured, and categorised to the point of losing any sense of neutral baseline. We know that the size and shape of a woman’s body is not always directly equivalent to her state of health, even though there may be overlap. We know that women are judged harshly, if unconsciously, for not abiding by societal norms. One study actually found that maternal attitudes towards their own weight, or self-image, was a more significant predictor of outcomes than actual weight. We also know that economic and cultural values, including generational or era-specific values, inform our aesthetic preferences which taint our ideas of what’s best or healthiest. Medical science is no more immune to cultural influence than any other discipline.
The whole tradition of monitoring and controlling a woman’s weight, with weekly weigh-ins that garner approval or scolding from medical authorities, comes from a tradition of paternalism that still has its unwelcome hands in maternity health. Aside from the possible uselessness of the information, another very real consequence is stress for the pregnant person, possibly mild worry if her weight happens to track according to expectations, and possibly a sense of shame and unworthiness if her weight should be outside the narrow margins of “normal”. This establishes, or at least contributes to, a dynamic in which the pregnant person risks feeling disempowered, which can affect her confidence in asking questions and making decisions about her own health care.
Weighing might be seen as a risk-free form of screening but we must be conscious of the benefit of tracking a pregnant person’s weight compared with the harm of causing stress, shame, or guilt. How much useful information do we really get from regular weighings?
According to the British National Healthcare System (NHS), not much. After conducting a huge study in the 1990’s, they concluded that regular weight tracking during pregnancy was not associated with any improvement in outcomes at all. If anything, they found it led to additional and completely unnecessary stress. So they phased the practice out completely. Now pregnant people get weighed once at the beginning for a baseline, and then not again unless there is a specific problem requiring that information. Weighing is done only as needed on an individual basis, rather than applied across the board as routine practice.
This is also true in the Netherlands, and plenty of other countries, many of which have very high rates of maternal and newborn health. Better than us, in fact. As of 2017, Canada was #41 In the world, whereas the Netherlands was #4. There, they do not indulge in routine gestational weighings, and clearly it has not led to any harm.
Sometimes studies that link obesity to poor outcomes actually further obfuscate the connection. This study, for example, which found an increase of medical interventions (induction and Caesarean births) associated with obesity, doesn’t seem to prove what it claims to prove. Instead it could be revealing our tendency to intervene when women are large, rather than discovering a medical connection. Also, the researchers claim that overweight women had large-for-dates babies, and underweight women had smaller-than-normal babies. But as noted above, this seems like a logical connection. Larger people will tend to create larger babies. Smaller people will make smaller babies. This is only a concern if we mistake “average” for “best”. There’s nothing inherently unhealthy about being tall or petite.
There is enough evidence that there is an association between maternal weight and gestational health that the topic is worth further attention, but it is less clear that controlling, or even tracking, weight gain is an effective solution. I suspect (and some studies agree) that a shift in emphasis towards nutrition, exercise, and lifestyle would yield more positive outcomes than isolating weight gain as the culprit. Maybe other forms of social and psychological support during pregnancy would help too, since weight retention can be linked to past or current trauma, which also affects maternal and infant health. Obviously, we also need financial support for low income families, since poverty is a well-known vector for poor nutrition. To truly improve outcomes, we might want to slide our lens towards the myriad of factors that cause extremes at both ends of the weight gain spectrum, and focus on those instead. Perhaps weight gain, as a by-product, would also be affected, but its importance would be irrelevant except as a soft indicator of maternal wellness.
So if you are at all confused by what you’ve read about how much weight to gain while you’re pregnant, you are not alone. It is a very confusing topic, with no universal agreement except that what you eat does indeed affect the baby. Prioritising whole foods, exercise, relaxation, and a generally healthy lifestyle are probably just as important as a number on a scale.
Stephanie Ondrack has been a member of the Childbearing Society since 2003.
She lives in East Van with her partner, 4 kids, 5 cats, 3 chickens, and 2 rats. You can read her thoughts on child development and learning at www.thesmallsteph.com