Abnormally low and excessively high weight gain during pregnancy have been linked to adverse outcomes. Low gestational weight gain is associated with perinatal mortality and small-for-gestational-age infants. Excessive gestational weight gain is associated with large-for-gestational-age infants and macrosomia, with adverse outcomes for mothers and infants. Although these associations have been recognized for many years, the specific role of weight change during pregnancy is unclear because low and high weight gains are associated with multiple other adverse factors. Stotland and colleagues studied the birth records at a large university medical center from 1980 to 2001 to better understand the role of weight gain during pregnancy in neonatal outcomes.

The authors used a database of more than 26,000 singleton births that included demographic, antenatal, intrapartum, delivery, and neonatal information. Reasons for exclusion from the study included multiple gestations, congenital abnormalities, chronic hypertension, diabetes, and birth before 37 weeks’ gestation. Each patient’s reported prepregnancy weight was taken as baseline, and all other weights were as documented in the chart. Pregnancy weight gain was classified in two ways. The first used the Institute of Medicine (IOM) guidelines (i.e., 28 to 40 lb [12.5 to 18.0 kg] for those with a low initial body mass index [BMI], 25 to 35 lb [11.5 to 16.0 kg] for normal BMI, and 15 to 25 lb [7.0 to 11.5 kg] for mothers with a high BMI. The second classification split weight gain into less than 15 lb or greater than 40 lb.

The neonatal outcomes measured were birth trauma, five-minute Apgar score of less than 7, use of assisted ventilation, small for gestational age, large for gestational age, umbilical arterial blood pH less than 7.1 or base excess less than −10, admission to neonatal intensive care unit or special care unit, neonatal infection, seizure, hypoglycemia, polycythemia, jaundice, meconium aspiration syndrome, respiratory distress or tachypnea, anemia, birth asphyxia, and perinatal death. Small for gestational age was defined as birth weight below the 10th percentile for California’s norm, and large for gestational age was defined as birth weight above the 90th percentile.

The final study included 20,465 births. Only 36.6 percent of mothers had weight gains within IOM guidelines. Most mothers (43.3 percent) gained more than recommended, and 29 percent gained more than 40 lb. Only 4.8 percent gained less than 15 lb. Gain within guidelines was more common in women with a low prepregnancy BMI. Conversely, women who were already overweight or obese were more likely to gain in excess of guidelines.

Compared with mothers whose weight gain was within the guidelines, those who gained less than 15 lb had increased rates of small-for-gestational-age infants, seizure, meconium aspiration syndrome, and prolonged hospital stay (see accompanying table). Conversely, almost all adverse neonatal outcomes were increased in mothers who gained more than 40 lb. In multivariate logistical regression analysis, weight gain below IOM guidelines remained significantly associated with small-for-gestational-age infants. Weight gain in excess of the guidelines remained significantly associated with a low five-minute Apgar score, large-for-gestational-age infants, seizure, hypoglycemia, polycythemia, and meconium aspiration syndrome. Weight gain above 40 lb also was associated with assisted ventilation.

The authors conclude that gestational weight gain in excess of guidelines is associated with several serious adverse neonatal outcomes. They express concern that the current obesity epidemic could fuel a secondary epidemic of excessive gestational weight gain with significant negative consequences for neonatal health. They call for public health measures to combat excessive weight gain during pregnancy.

editor’s note: Obesity in pregnant women has recently become a leading topic of discussion in Britain. In addition to the adverse neonatal outcomes discussed in the above study, the British press draws attention to greater rates of pregnancy complications in obese women, especially gestational diabetes and hypertension, and higher rates of operative delivery. Obesity also can complicate the performance and interpretation of ultrasound scans.

Health services are reported to be spending significant sums to accommodate obese mothers. Adjustments range from reinforced operating tables to longer epidural needles. The best approach is to begin pregnancy at a healthy weight—one more reason to tackle obesity vigorously early in life.—a.d.w.