Association between gestational weight gain and preterm birth and post-term birth: a longitudinal study from the National Vital Statistics System database.

Background: To evaluate the association between gestational weight gain (GWG) and preterm birth and post-term birth.

Methods: This longitudinal-based research studied singleton pregnant women from the National Vital Statistics System (NVSS) (2019). Total GWG (kg) was converted to gestational age-standardized z scores. The z-scores of GWG were divided into four categories according to the quartile of GWG, and the quantile 2 interval was used as the reference for the analysis. Univariate and multivariate logistic regression analyses were performed to investigate the association between GWG and preterm birth, post-term birth, and total adverse outcome (preterm birth + post-term birth). Subgroup analysis stratified by pre-pregnancy body mass index (BMI) was used to estimate associations between z-scores and outcomes.

Results: Of the 3,100,122 women, preterm birth occurred in 9.45% (292,857) population, with post-term birth accounting for 4.54% (140,851). The results demonstrated that low GWG z-score [odds ratio (OR): 1.04, 95% confidence interval (CI): 1.03 to 1.05, P < 0.001], and higher GWG z-scores (quantile 3: OR: 1.42, 95% CI: 1.41 to 1.44, P < 0.001; quantile 4: OR: 2.79, 95% CI: 2.76 to 2.82, P < 0.001) were positively associated with preterm birth. Low GWG z-score (OR: 1.18, 95% CI: 1.16 to 1.19, P < 0.001) was positively associated with an increased risk of post-term birth. However, higher GWG z-scores (quantile 3: OR: 0.84, 95% CI: 0.83 to 0.85, P < 0.001; quantile 4: 0.59, 95% CI: 0.58 to 0.60, P < 0.001) was associated with a decreased risk of post-term birth. In addition, low GWG z-score and higher GWG z-scores were related to total adverse outcome. A subgroup analysis demonstrated that pre-pregnancy BMI, low GWG z-score was associated with a decreased risk of preterm birth among BMI-obesity women (OR: 0.96, 95% CI: 0.94 to 0.98, P < 0.001).

Conclusion: Our result suggests that the management of GWG may be an important strategy to reduce the number of preterm birth and post-term birth.