For women carrying twins, timing is important when it comes to putting on pregnancy pounds. The findings of a new study conducted at the University of California in San Diego (UCSD) indicate there is an 8-week window of opportunity during the second trimester to achieve ideal pregnancy weight and reduce the risk of preterm delivery.

Dr. Kate Pettit, a specialist in maternal-fetal medicine at UCSD, presented the findings of her study at the 2014 Annual Clinical Meeting of the American Congress of Obstetricians and Gynecologists. She and her research team studied maternal records of twins born between 2009 and 2013 at UCSD medical facilities.

During that period of time, 489 deliveries of twins took place at UCSD facilities. The Pettit research team gathered weight records for each mother at various points during pregnancy:

  • Before week 14
  • Week 20
  • Week 28
  • Last doctor visit before delivery

Some findings of the study revealed:

Average weight gain throughout pregnancy was:

  • 1.058 pounds (0.48 kilograms [kg]) per week for first 20 weeks
  • 1.433 pounds (0.65 kg) for weeks 20 to 28
  • 1.301 pounds (0.59 kg) per week for the entire pregnancy

Ninety-three of the women did not gain this much weight during pregnancy.

The women who did not gain the average amount during weeks 20 to 28 were more likely to delivery earlier than week 32 than those who gained an adequate amount during those eight weeks:

  • 32% gaining inadequate weight had preterm deliveries
  • 14% gaining an adequate amount had preterm deliveries
  • 26% who did not gain adequately during weeks 20 to 28 had spontaneous preterm deliveries
  • 9% who did gain adequate weight experienced spontaneous preterm deliveries

The Pettit team found inadequate weight gain during this period of pregnancy (weeks 20 to 28) was the strongest predictor of preterm birth identified in the study. The study, however, did not attempt to discover the mechanism that causes these preterm births.

A recommendation for weight gain when pregnant with twins was issued in 2009 by the Institute of Medicine (IOM), prompting the Pettit study. The 2009 IOM recommendation calls for gaining about one pound (0.5 kg) per week, or a total pregnancy weight gain between 37 to 54 pounds.

The IOM revised its recommendation for pregnant women who are overweight or obese. The 2013 revision says an obese woman with a pregnancy progressing normally, including normal fetal size, is perfectly fine if she does not gain any extra weight during pregnancy.

Source: Pullen, Lara C, Ph.D. “Poor Midterm Weight Gain Linked to Preterm Birth of Twins.” Medscape Multispecialty. WebMD LLC. Apr 29, 2014. Web. May 9, 2014.