Gestational weight gain standards based on women enrolled in the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project: a prospective longitudinal cohort study

Abstract

Objective: To describe patterns in maternal gestational weight gain (GWG) in healthy pregnancies with good maternal and perinatal outcomes.

Design: Prospective longitudinal observational study.

Setting: Eight geographically diverse urban regions in Brazil, China, India, Italy, Kenya, Oman, United Kingdom, and United States, April 2009 to March 2014.

Participants: Healthy, well nourished, and educated women enrolled in the Fetal Growth Longitudinal Study component of the INTERGROWTH-21(st) Project, who had a body mass index (BMI) of 18.50-24.99 in the first trimester of pregnancy.

Main outcome measures: Maternal weight measured with standardised methods and identical equipment every five weeks (plus/minus one week) from the first antenatal visit (<14 weeks' gestation) to delivery. After confirmation that data from the study sites could be pooled, a multilevel, linear regression analysis accounting for repeated measures, adjusted for gestational age, was applied to produce the GWG values.

Results: 13,108 pregnant women at <14 weeks' gestation were screened, and 4607 met the eligibility criteria, provided consent, and were enrolled. The variance within sites (59.6%) was six times higher than the variance between sites (9.6%). The mean GWGs were 1.64 kg, 2.86 kg, 2.86 kg, 2.59 kg, and 2.56 kg for the gestational age windows 14-18(+6) weeks, 19-23(+6) weeks, 24-28(+6) weeks, 29-33(+6) weeks, and 34-40(+0) weeks, respectively. Total mean weight gain at 40 weeks' gestation was 13.7 (SD 4.5) kg for 3097 eligible women with a normal BMI in the first trimester. Of all the weight measurements, 71.7% (10,639/14,846) and 94.9% (14,085/14,846) fell within the expected 1 SD and 2 SD thresholds, respectively. Data were used to determine fitted 3rd, 10th, 25th, 50th, 75th, 90th, and 97th smoothed GWG centiles by exact week of gestation, with equations for the mean and standard deviation to calculate any desired centiles according to gestational age in exact weeks.

Conclusions: Weight gain in pregnancy is similar across the eight populations studied. Therefore, the standards generated in this study of healthy, well nourished women may be used to guide recommendations on optimal gestational weight gain worldwide.

Fig 1 Flowchart for selecting women included in study of gestational weight gain

Fig 2 Trajectories of gestational weight gain of 100 randomly selected normal weight healthy women with uncomplicated live singleton births

Fig 3 Standardised site difference (SSD) for gestational weight gain in the Fetal Growth Longitudinal Study of the INTERGROWTH-21^st Project. SSD calculated by (site mean of gestational weight gain at each gestational age interval minus all sites mean of gestational weight gain at the same gestational age interval)/all sites’ SD of gestational weight gain at the same gestational age interval. SSD was adjusted at median gestational age for all sites at each gestational age interval

Fig 4 Fitted 3rd (bottom dashed line), 50th (middle dashed line), and 97th (top dashed line) smoothed centile curves for gestational weight gain among normal weight women. Large blue circles show empirical values for each week of gestation, and small grey circles show actual observations

Fig 5 Smoothed centile curves at 3rd, 10th, 50th, 90th, and 97th centiles for gestational weight gain among healthy normal weight women with uncomplicated live singleton births