Prenatal weight gain patterns and spontaneous preterm birth among nonobese black and white women

Abstract

Evidence for the relationship of prepregnancy weight and prenatal weight gain to preterm delivery (PTD) is mixed; several important methodological issues have prevented the drawing of firm inferences. The objective of this study was to examine, by trimester, the relationship of prenatal weight gain (total, rate) to spontaneous PTD among low-income high-risk nonobese (body mass index: BMI ≤26.0) black (677) and white (338) multiparous women. Sociodemographic data, reproductive history, and reported prepregnancy weight were obtained by interview during the first prenatal visit. Weight and height were measured without shoes in light clothing, using standard anthropometric procedures. Total gain (kg) and rate of gain (kg/wk) were calculated as follows: first trimester (last weight observation during gestational ages [GA] 10–13 wks minus prepregnancy weight); second trimester (last weight during GA 24–27 wk minus first weight during 14–18 wk); third trimester (last weight prior to delivery minus first weight during GA 28–32 wk). Results revealed that >70% of PTD was at 32–36 wk GA. PTD was higher among black (12.4%) than white (8.0%) women (p=0.033). PTD was higher among white (11.9%) than black (5.1%) women with low prepregnancy BMI (p=0.027). While 45% of the women gained less than current Institute of Medicine guidelines by BMI in the first trimester, and from 22 to 37% gained less than these guidelines during the second trimester, in regression analysis neither total nor rate of gain was associated with GA or PTD. However, third trimester rate of gain (kg/wk) was positively associated with GA for all women (p=0.005) and for black women (p=0.026) with low prepregnancy BMI, but not for white women or for women with normal BMI. These data suggest that the impact of weight gain pattern on PTD varies by prepregnancy BMI, ethnicity, and trimester, and is greatest during the third trimester among women with low BMI.