Identifying critical windows for macrosomia prevention: a study on the association between phase-specific dynamic BMI...

To examine the correlation among pre-pregnancy body mass index (BMI), BMI increments during different gestational periods, and the occurrence of macrosomia in singleton full-term pregnant women without complications. Additionally, we aimed to assess the predictive performance of these BMI-related indicators for macrosomia, thereby identifying key time windows for targeted gestational weight management.

An analytical approach was adopted, entailing a retrospective evaluation of clinical data from 4,218 pregnant women without complications who underwent regular prenatal examinations and singleton full-term delivery during the period between January 2019 and December 2025 at the Jinshan Branch of Shanghai Sixth People's Hospital. Based on neonatal birth weight, a case-control design was employed, selecting 200 cases of macrosomia (macrosomia group) and 250 cases of normal birth weight infants (control group). Data including pre-pregnancy BMI, baseline BMI at the first prenatal visit (10-13 weeks), and BMI at various stages of mid- and late-pregnancy (20, 24, 28, 32, 36 weeks, and before delivery) were collected to calculate BMI increments for each stage. The predictive efficacy of individual BMI indicators and a combined model for macrosomia was evaluated using independent sample t-tests, Pearson correlation analysis (PCA), and receiver operating characteristic (ROC) curves.

(1) Increased pre-pregnancy BMI was significantly and positively correlated with an increased macrosomia risk. Pre-pregnancy overweight (OR = 2.63) and obesity (OR = 9.06) emerged as independent risk contributors for macrosomia (P < 0.01). (2) Baseline BMI at 10-13 weeks, along with BMI increments during the 32-36 weeks period and the period from 36 weeks to delivery, exhibited a significant increase in the macrosomia group in comparison to the control group (P < 0.05). (3) The analysis of correlation demonstrated a moderate positive correlation between baseline BMI at 10-13 weeks and neonatal birth weight (r = 0.386, P < 0.001). However, no significant correlation was identified between mid-pregnancy BMI increments and birth weight (P > 0.05). (4) Utilising ROC curve analysis, it was ascertained that baseline BMI at 10-13 weeks exhibited the most optimal predictive efficacy among the individual indicators (AUC = 0.73), with the late-pregnancy increment indicators following in succession. The combined predictive model, integrating early-pregnancy BMI and late-pregnancy BMI increments, achieved a superior AUC of 0.84.

Pre-pregnancy BMI, early-pregnancy (10-13 weeks) BMI, and late-pregnancy (32 weeks to delivery) BMI increments are critical predictors of macrosomia in pregnant women without complications. Specifically, baseline BMI at 10-13 weeks serves as a core indicator for early risk identification. Clinical interventions should focus on these two critical stages-early and late pregnancy-to implement individualized weight management, thereby effectively reducing the incidence of macrosomia and improving maternal and neonatal outcomes.