Many women of size gain little or no weight in pregnancy and are
perfectly fine. However, research shows there is room for
concern in promoting limited weight gain as a goal for all
women of size.
A very low weight gain increases the risk for prematurity,
small-for-gestational-age babies (SGA), and possibly
stillbirth. Although the association between low weight gain
and these outcomes is less strong in "obese" women, the
risk IS still increased and caution is therefore prudent. I
particularly worry about the recent trend telling women of size to
gain NO weight or even to LOSE weight during pregnancy.
Weight gain in women of size is highly variable. I've been
collecting informal data via my website and casual
surveys among women of size for years and my data -- plus data
from official studies -- seems to confirm that weight gain in
women of size is all over the map. On average, we definitely
gain less than women of average size, but if you look at
individuals the results are highly varied. A few lose weight
during pregnancy, some gain almost nothing, most gain around
10-15 lbs., many gain 15-25 lbs., and a few gain more.
Doctors usually assume that differing weight gains result from
differences in caloric intake and habits, but I don't see
that. It's not irrelevant, but there's certainly not the
direct connection many care providers expect. A high BMI
woman who gains 20 lbs. doesn't necessarily have worse
habits than another who gains almost nothing. There are
a lot more variables than that.
Women of size probably gain less on average because we already
have fat reserves and physiologically do not need more for
pregnancy. Also, many of us find that pregnancy revs up an
otherwise-sluggish metabolism, which leads many of us to gain
less. However, women who are chronic dieters or who have
recently lost a lot of weight tend to have much
higher weight gains. And there are many other
factors too....which is why prenatal gain is SO variable in women
of size and doesn't necessarily coordinate with habits and
Degree of "obesity" is another variable to consider.
Recent research shows that class I obese women (BMI 30-35) who gain
very little weight are at far more risk for poor outcomes than
class III obese women (BMI 40+) who gain little. But that
doesn't mean that no gain or weight loss in "morbidly obese"
women is benign either.
Studies on restricting weight gain in women of size show varying
rates of success. Some find that regular nutritional consults
and regular exercise help high BMI women gain less, but they also
find that even on such a program, many "obese" women gain more than
15 lbs, despite doing everything "right." It's not just about
intake and habits.
Alarmingly, several of these studies found that the rate of
too-small (SGA) babies increased in the women who gained little in
pregnancy, but the authors consistently shrug off this finding as
unimportant. Many of the studies also conveniently do not
examine prematurity or stillbirth rates, or are not large enough to
conclude that no-gain interventions are safe. None of the
studies involve long-term follow-up of babies exposed to restricted
intakes, and few monitor the mothers for ketones (some research
shows high or consistent levels of ketones may lead to cognitive
impairment in the child).
Therefore, I have strong reservations about strictly limiting
weight gain in women of size. Personally, I think a dogmatic
approach -- placing the goal on what the scale says rather
than the daily nutrition and exercise of the mom -- is the wrong
emphasis. Don't manipulate a woman's nutrition to meet
an arbitrary weight gain goal. Instead, emphasize
excellent nutrition and regular exercise, and trust the woman's
body to gain what it needs.
Personally, I am a class III "morbidly obese" woman and I gained
about 5 lbs. net in each of my pregnancies. This was fine for
me because my nutrition was fine; it didn't come from strictly
limiting intake or not being "allowed" to gain
weight. It was just my body's natural response to the
increased metabolism of pregnancy. A small gain is not
automatically harmful, as long as the mom is getting good
nutrition, is not spilling a lot of ketones, etc. But
promoting this as a goal and/or using draconian methods to get it
-- THAT has a lot of potential for harm, in my opinon, and I have
grave reservations about the current push to limit gains so
I have a whole series on the topic of prenatal weight gain in
women of size going on in my blog currently, complete with links to
study references. I should have the latest post on the topic
up soon, so I invite readers to come over and read more about it
Look in the category of weight gain in pregnancy.