Preconceptional and gestational weight trajectories and risk of delivering a small-for-gestational-age baby in rural Gambia

Abstract

Background: Maternal nutritional status is a key determinant of small for gestational age (SGA), but some knowledge gaps remain, particularly regarding the role of the energy balance entering pregnancy.Objective: We investigated how preconceptional and gestational weight trajectories (summarized by individual-level traits) are associated with SGA risk in rural Gambia.Design: The sample comprised 670 women in a trial with serial weight data (7310 observations) that were available before and during pregnancy. Individual trajectories from 6 mo before conception to 30 wk of gestation were produced with the use of multilevel modeling. Summary traits were expressed as weight z scores [weight z score at 3 mo preconception (zwt_{-3 mo}), weight z score at conception, weight z score at 3 mo postconception, weight z score at 7 mo postconception (zwt_{+7 mo}), and conditional measures that represented the change from the preceding time] and were related to SGA risk with the use of Poisson regression with confounder adjustment; linear splines were used to account for nonlinearity.Results: Maternal weight at each time point had a consistent nonlinear relation with SGA risk. For example, the zwt_{-3 mo} estimate was stronger in women with values ≤0.5 (RR: 0.736; 95% CI: 0.594, 0.910) than in women with values >0.5 (RR: 0.920; 95% CI: 0.682, 1.241). The former group had the highest observed SGA prevalence. Focusing on weight change, only conditional zwt_{+7 mo} was associated with SGA and only in women with values >-0.5 (RR: 0.579; 95% CI: 0.463, 0.724).Conclusions: Protection against delivering an SGA neonate offered by greater preconceptional or gestational weight may be most pronounced in more undernourished and vulnerable women. Independent of this possibility, greater second- and third-trimester weight gain beyond a threshold may be protective. This trial was registered at http://www.isrctn.com/ as ISRCTN49285450.

Keywords: age-related trajectories; gestational weight gain; maternal nutrition; prepregnancy weight; small for gestational age.

FIGURE 1

Sample average-weight trajectory from 6 mo preconception to 30 wk gestation in 670 Gambian women according to the season of conception as estimated from the multilevel model reported in Supplemental Table 1.

FIGURE 2

Diagram depicting paths from maternal weight at different time points to SGA, estimated by using a path model applied to a subset of 400 Gambian women and infants. SGA was defined according to a birth weight for gestational age <10th percentile of the INTERGROWTH-21st standard. The model was applied to a subset of participants with a zwt_{−3 mo} ≤0.5 z scores in whom there was a protective association of a zwt_{−3 mo} with SGA risk (Table 2)_. The model was adjusted for season of birth, sex, parity, maternal age at booking, maternal height at booking, and intervention. With the use of only data on the subset of participants, maternal weight z scores were recalculated internally (i.e., observation − mean ÷ SD) at each time point with the use of the individual weights (kilograms) that were estimated from the multilevel model shown in Supplemental Table 1. SGA, small for gestational age; Zwt, weight z score.