Interpregnancy Weight Gain Risky for Second Pregnancy

BOSTON, Sept. 29 -- Mothers who gained weight between pregnancies increased their risk for maternal and perinatal complications during the second consecutive pregnancy, according to a large Swedish study.

These risks, which included pre-eclampsia, gestational hypertension and diabetes, cesarean delivery, stillbirth, and large-for-gestational age births, held even if the women were not medically overweight, researchers here and in Stockholm reported in the Sept. 30 issue of the Lancet.

Analysis of a nationwide cohort of 151,025 women whose first two singleton births occurred from 1992 to 2001 suggests that even a modest increase of one to two units of body mass index (BMI) before the second pregnancy could result in perinatal complications, said Eduardo Villamor, M.D., of the Harvard School of Public Health here and Sven Cnattingius, M.D., of the Karolinska Institute in Stockholm.

On average, women gained just over half a BMI unit (median 0.7 unit (IQR -0.3 to 1.7)) during a mean interpregnancy interval of 24 months. Weight gain between pregnancies decreased with age, education, height, and BMI at the first pregnancy, and was lower in women of Nordic origin, the researchers said.

After adjustment for potential confounders, the researchers found that the risks were linearly related to the amount of weight change between pregnancies, starting at only one to two BMI units, and continuing to increase progressively thereafter.

For example, the researchers said, a gain of only one to two BMI units during an average two years would increase the risk of gestational hypertension, diabetes, or extra large birth weight by an average 20% to 40%, and a further linear increase would follow weight gain. Because of the large sample size and the general consistency of the associations found, the researchers said, the findings are not likely to be due to chance.

Compared with women whose BMI changed between minus 1.0 and 0.9 units, the adjusted odds ratios for adverse pregnancy outcomes for those who gained three or more units (about 17 pounds in a woman about 5.5 feet tall) during an average two years were as follows: pre-eclampsia, 1.78 (95% CI 1.52-2.08); gestational hypertension 1.76 (1.39-2.23); gestational diabetes 2.09 (1.68-2.61); cesarean delivery 1.32 (1.22-1.44); stillbirth 1.63 (1.20-2.21); and large-for-gestational-age birth 1.87 (1.72-2.04).

For example, the adjusted odds of stillbirth were 63% greater in women who gained three or more BMI units between pregnancies compared with those whose weight changed by less than one BMI unit (P=0.002). This risk increased significantly as weight gain increased, the researchers said and was independent of obesity-related disease in pregnancy such as pre-eclampsia or diabetes.

By contrast, the researchers said, the risks of maternal pre-eclampsia and gestational oversize in the newborn fell significantly in women who lost at least one BMI unit between pregnancies, while their risk of gestational diabetes and hypertension remained at general population levels.

In the study, only 5.4% of the women were obese at the outset. To examine whether the effects of weight gain were independent of those for overweight or obesity, the researchers analyzed the risks of adverse pregnancy outcomes in relation to weight change in a subset of 97,558 women who had a pre-pregnant BMI of less than 25 for both pregnancies. The findings of increased risk with weight gain, they said, were more or less the same as those reported for the whole population.

"Our study underscores the importance of avoiding weight gain between pregnancies and accords with the view that even a moderately increased BMI could be deleterious for maternal and neonatal health," the researchers wrote.

Among the study's limitations, the researchers noted is that it was the inability to determine whether large weight gains before the first pregnancy, for example, or after the second pregnancy would result in similar increases in the incidence of obstetric complications.

It is also possible, they said, that residual confounding factors, such as other risk factors or illnesses, could be associated with both interpregnancy weight gain and gestational outcomes. Additionally, they said, they did not have information for week of gestation at the first prenatal visit, thereby affecting the estimate of interpregnancy weight change.

Despite these limitations, Drs. Villamor and Cnattingius wrote, "Our results provide robust epidemiological evidence for advocating weight loss in overweight and obese women who are planning to become pregnant and, more importantly, to prevent weight gain before pregnancy in the larger population of women of healthy weight."

A combination of dietary modification and exercise may also be effective in avoiding postpartum weight retention. "Assessment of whether these interventions can be successfully implemented at the population level is a crucial pending task," they concluded.

Commenting on the study in the same Lancet issue, Aaron Caughey, M.D., of the University of California San Francisco, said that although it does seem that even modest changes in BMI are associated with increased perinatal morbidity and stillbirth, it is unclear whether weight loss before pregnancy would lead to improved outcomes.

Although the researchers found that women with a BMI decrease of more than one unit had lower rates of pre-eclampsia and large-for-gestational stage infants, only 5.4% of the women in the study were obese, he wrote. Therefore a related question is whether such small amounts of weight loss in obese and morbidly obese women would lead to similar benefits.

With such questions remaining, the study should lead to a call for more randomized trials of weight-loss interventions before pregnancy as well as post-partum. With the recent increase in obesity in the developed world, such interventions, he said, are likely to affect not only future pregnancies, but also long-term outcomes in women's health.