How Much Weight Gain Is Healthy During Pregnancy?

Eating for two -- I wish I knew where that phrase came from. I suppose it has been around since the beginning of time, but it is the bane of the obstetrical world. Why? Because pregnant women are getting too fat. You will hear many a pregnant woman say, "I'm having a baby and now I have to eat for two. So, I'm just going to stop by the store and get me a quart of Häagen-Dazs?"

That wasn't always the case. In the 1940s and 1950s, obstetricians were telling their patients to gain no more than 20 pounds during their pregnancies for fear of the patient developing preeclampsia (toxemia), a disorder in pregnancy that leads to seizures and increased complications for mother and baby. However, for the past 25 years, the standard obstetric approach to maternal weight gain during pregnancy has been to follow the American College of Obstetricians and Gynecologists (ACOG) recommendation which stated, "Regardless of how much women weigh before they become pregnant, gaining between 26-35 pounds during pregnancy can improve the outcome of pregnancy and reduce their chances of having the pregnancy end in fetal death".

After this dictum was announced (to many obstetricians' chagrin), it became common practice for pregnant women to be told "to eat to appetite" with little other dietary direction. Even in 1990, the Institute of Medicine (IOM) recommended a minimum of 15 pounds weight gain for obese women. Even with the updated 2009 IOM guidelines, obese women are asked to gain between 11 and 20 pounds; which, in my opinion, is entirely too much if the patient starts the pregnancy over 200 pounds.

The fact of the matter is that you are not eating for two, you are eating for one and a twentieth. A baby at term weighs six or seven pounds; if you are a 140-pound woman, that seven-pound baby is one-twentieth the size of you, so there is no reason in the world to eat for two you's. Obesity has become endemic in the United States. Over 35 percent of adult women are considered to be obese.

Currently, 20 percent of all American women are obese at the beginning of their pregnancy. Obesity has been recognized as a risk factor in pregnancy for more than 50 years with various pregnancy complications which include gestational diabetes, preeclampsia, large babies, operative risks, wound infections and a two-fold higher risk of primary cesarean delivery.

An important source of complications in pregnancy, in my opinion, is excessive weight gain. In addition to the increased risk of developing gestational diabetes, obesity is more likely to lead to postpartum depression after the baby is born. Several studies have even linked obesity in pregnancy with an increase in the incidence of neural tube defects (spina bifida) and heart defects.

A pregnant woman should gain only two pounds in the first trimester (before 12 weeks). At 12 weeks, the baby weighs 14 grams. An ounce is 30 grams; so a 14-gram fetus is not even half an ounce, which means there is no reason for a 10-pound weight gain. After the first trimester, weight gain should be three-quarters of a pound to one pound per week for the remainder of the pregnancy, for a total weight gain during pregnancy of 24 to 26 pounds.

Why that much even? Because there is a baby in there, which makes for seven pounds. Then there is the weight of the placenta (11/2 lbs), the amniotic fluid (2 lbs), and the increased size and weight of the uterus (21/2 lbs). The breasts, affected by hormones, become about one pound heavier. The blood volume is increased in pregnancy (31/2 lbs), as is the deposition of fat, which should be held to six or seven pounds. A lot of structural changes do occur in pregnancy. But they do not add up to 65 pounds' worth of weight gain.

A 30-pound weight gain for an appropriate-weight pregnant woman is still all right, but, in my experience, if you tell a woman 30 pounds, she will gain 40 or even 50 pounds during her pregnancy. Losing those pounds later may prove to be impossible. Before the baby arrived, you had time and energy to go to the gym. After delivery, however, your whole life changes, and your intention to get back to your pre-pregnancy weight often goes by the board.

Back in the 1970s, Weight Watchers had a pregnancy weight control plan that went a long way in ensuring that the member and her baby were healthy. However, with the medical-legal implications inherent with taking care of pregnant women, they too have backed off regarding healthy eating during pregnancy in obese women. Because of my fascination with obesity and pregnancy, I embarked on a clinical trial back in 1998 that would challenge the dogma that all pregnant women, regardless of their weight, should gain between 26 and 35 pounds. It took me seven years to complete. That study, the first of its kind, was published in 2009 in the Journal of the National Medical Association and it showed that obese women need not gain any weight during their pregnancies. The study (monitored) group gained only 11 pounds during their pregnancies while the control (unmonitored) group gained 31 pounds.

It was a landmark study and rather than focusing on a numerical end-point (numbers on a scale) with respect to weight in obese pregnant women, obstetricians should promote adherence to a monitored, well-balanced nutritional program. The take-home message for obese pregnant women is that they should be eating twice as well, not twice as much.

Yvonne S. Thornton, M. D., M. P. H., Sc. D. (hon), FACOG, FACS

Note: The above opinions are my own and do not necessarily reflect the policies or practices of my affiliated medical school or medical center.

EDITOR'S NOTE: For another perspective read the The American College of Obstetricians and Gynecologists (ACOG) first official opinion on obesity during pregnancy.