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

Background: Maternal nutritional status is a key determinant of small-for-gestational age (SGA), but there remain some knowledge gaps, particularly regarding the role of energy balance entering pregnancy. Objective: This study investigates how pre-conceptional 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 (ISRCTN49285450), with serial weight data (7,310 observations) available before and during pregnancy. Individual trajectories from six months pre-conception to 30 weeks gestation were produced using multilevel modelling. Summary traits were expressed as weight Z-scores (Zwt-3 months pre-conception, Zwt0 months (i.e., conception), Zwt+3 months post-conception, Zwt+7 months post-conception, and conditional measures representing change from the preceding time) and related to SGA risk using Poisson regression with confounder adjustment; linear splines were used to account for non-linearity. Results: Maternal weight at each time had a consistent non-linear relationship with SGA risk. For example, the Zwt-3 months estimate was stronger in women with values ≤ 0.5 Z-scores (relative risk 0.736; 95% confidence interval 0.594, 0.910) than in women with values > 0.5 Z-scores (0.920; 0.682, 1.241). The former group had the highest observed SGA prevalence. Focusing on weight change, only Conditional Zwt+7 months was associated with SGA, and only in women with values > -0.5 Z-scores (0.579; 0.463, 0.724). Conclusions: Protection against delivering an SGA neonate offered by greater pre-conceptional or gestational weight may be most pronounced among more undernourished and vulnerable women. Independently of this, greater second/third trimester weight gain beyond a threshold may be protective.