Gestational Weight Gain and Preterm Birth Are Linked in Twin Pregnancies

Most weight-related studies of late have examined the effects of overweight and obesity on various aspects of women’s health. However, a new award-winning study presented today at ACOG’s 2014 Annual Clinical Meeting in Chicago has examined the relationship between inadequate gestational weight gain and preterm birth before 32 weeks’ gestation in normal-weight, overweight, and obese women pregnant with dichorionic/diamniotic or monochorionic/diamniotic twins. What makes this study different than other studies evaluating inadequate weight gain in pregnancy is that this study looked at a specific period during the pregnancy-the second trimester-instead of total weight gain over the course of the entire pregnancy.

To calculate adequate weight gain, Kate E. Pettit, MD, of the University of California, San Diego, and colleagues divided the 2009 Institute of Medicine-recommended minimum total gestational weight gain by 37 weeks (Table). For normal-weight women, this represented a minimum weekly gain of 0.45 kg, or about 1 lb/wk. Then, they evaluated weight gain at 20 to 28 weeks’ gestation in 489 women with twin pregnancies.

The average maternal age at delivery was 32 years. About 60% of the participants were normal weight, 20% were overweight, and 20% were obese.

Before 20 weeks’ gestation, about 40%
of women had inadequate weight gain. However, at 20 to 28 weeks’ gestation,
about 19%, or 93 women, had inadequate weight gain.

The 93 women who gained less than the minimum recommended weight at 20 to 28 weeks’ gestation were nearly 3 times more likely to give birth before 32 weeks’ gestation than women who had adequate weight gain during the same gestational period (40% vs 15%, respectively), said Pettit. Compared with women in the adequate weight gain group, women with inadequate weight gain had higher rates of gestational diabetes, lower rates of preeclampsia or HELLP syndrome, and equivalent rates of cesarean delivery.

In addition, inadequate weight gain was associated with spontaneous preterm birth but not associated with indicated preterm birth. Monochorionicity and cervical length less than 2.5 cm were also associated with preterm birth before 32 weeks’ gestation, as expected. However, advanced maternal age, BMI category, and inadequate weight gain prior to 20 weeks’ gestation was not associated with preterm birth.

Inadequate weight gain was the strongest predictor of preterm birth before 32 weeks’ gestation in this study group. The biological plausibility of this association is unknown, said Pettit. However, she suggested that these findings may reveal an opportunity to help reduce the rate of preterm birth. Specifically, the second trimester may be an optimal time for ob/gyns to discuss the importance of nutrition and adequate weight gain with women who have gained less than the recommended amount of weight during pregnancy.

Of note, approximately 60% of the twin pregnancies in this study were conceived spontaneously, and the remaining 40% were conceived through assisted reproductive technology methods. Pettit and colleagues did not examine the differences in rates of preterm birth between groups based on conception type, but she did say that the data is there to do so.