Based upon a small number of special cases, obese pregnant women now are being told they should lose weight while larger studies just suggest them to curb weight gain to certain limits.
It is no secret that very heavy women, when pregnant, are at risk of getting a diabetes. In such a case, nothing can be said against interventions tackling this disease, in particular, a switch to eating healthier food and to more physical activity. Such an intervention has been undertaken in ninety-six women with gestational diabetes, using diet and exercise, in St. Louis, Missouri.
In these diabetic pregnant women, diet alone or diet plus exercise reduced the risk of big (macrosomic) babies if the women maintained a stable weight in spite of their pregnancy. A minority of women even lost some weight. Based upon this special and very limited experience, the general advice has been spread by certain media that heavy-weight pregnant women should lose weight.
Larger studies suggest to curb weight gain, not to lose weight
Interestingly, another study has just recently been published by the Missouri researchers, about weight gain and pregnancy outcomes in obese women. Based upon data of more than a hundred thousand pregnant women, the authors report:
"Gestational weight gain incidence for overweight or obese pregnant women, less than the currently recommended 15 lb, was associated with a significantly lower risk of preeclampsia, cesarean delivery, and large for gestational age birth and higher risk of small for gestational age birth." (emphasis mine)While high blood pressure (preeclampsia), cesarean delivery and large babies are complications that may harm mother and baby, a low birth weight is a serious health risk for the baby. Given the wide variance in baby weights, the amount of recommended weight gain of mothers, in my opinion, cannot follow a general rule but must be based on the ultrasound pictures in every single case: If the fetus is large for his age, weight gain may be more restricted than in cases of a small fetus.
Swedish guidelines are not so harsh
In Sweden, the optimal pregnancy weight gain for body mass index categories of women has been assessed, using data of nearly three hundred thousand women of all weight categories. The upper limit of optimal weight gain in pregnancy is 22 lb (10 kg) for lean women up to a body mass index (BMI) of twenty-five, 20 lb (9 kg) for women up to BMI thirty, and 13 lb (6 kg) for a BMI above thirty.
Limited value of large numbers
If medical studies, based upon the law of large numbers, show certain effects such as a link between pregnancy weight gain and pregnancy outcome, these results cannot be applied to a single woman who is pregnant and anxious about her health and the future health of her baby. Thus, such guidelines must be seen with caution, and instead of looking anxiously at the scale, a woman most likely will fare better by listening to her body and its needs.