Objectives: To estimate the association between estimated fetal weight (EFW) percentiles on the INTERGROWTH-21st and WHO fetal growth charts and kindergarten-age childhood development, and identify the charts’ percentile cut-offs that best predict kindergarten-age developmental challenges. Design: Retrospective cohort linkage study. Setting: Obstetrical ultrasound department of BC Women’s Hospital, Vancouver, Canada. Population or Sample: Non-anomalous, singleton fetuses scanned ≥ 28 weeks’ gestation, 2000-2011 (n=3418). Methods: We classified EFWs into percentiles using the INTERGROWTH-21st and WHO charts. We used generalized additive modelling to link EFW percentile with routine province-wide kindergarten readiness test results. We calculated the AUC, as well as other measures of diagnostic accuracy with 95% confidence intervals (CI) at select percentile cut-points of the charts. Main Outcome Measures: Total Early Development Instrument (EDI) score (/50). Secondary outcomes: EDI sub-domain scores for language and cognitive development, and for communication skills and general knowledge; designation of ‘developmentally vulnerable’ or ‘special needs’. Results: Fetuses with lower EFW percentiles had systematically lower EDI scores and increased risks of developmental vulnerability. However, the clinical significance of differences was modest in magnitude: e.g., total EDI score -2.8 [95% CI: -5.1, -0.5] in children with an EFW 3-9th percentile of INTERGROWTH chart (vs. reference of 31-90th). The charts’ predictive abilities for adverse child development were limited (e.g., AUC<0.53 for both charts). Conclusions: Lower EFW percentiles on the INTERGROWTH-21st and WHO charts indicate increased risks of adverse kindergarten-age child development at the population level, but are not accurate individual-level predictors of adverse child development.

Objectives To assess associations between pre-pregnancy BMI and severe maternal morbidity (SMM), perinatal death and neonatal morbidity in twin pregnancies. Design Retrospective cohort study. Setting British Columbia, Canada (2000-2017). Population All twin births at ≥20 weeks’ gestation. Methods We examined associations between pre-pregnancy BMI, categorized as underweight (BMI <18.5m/kg2), normal BMI (18.5m/kg2 BMI <25m/kg2), overweight (25m/kg2 BMI <30m/kg2) and obese (BMI ≥30m/kg2) and adverse maternal and perinatal outcomes, using targeted maximum-likelihood estimation, adjusted for demographics and obstetric history. Outcomes SMM, perinatal death, severe perinatal morbidity. Results Overall, 7770 (368 underweight, 1704 overweight and 1016 obese) women with twin pregnancy were included. The rates of SMM (per 10,000 pregnancies) were: 271.1, 320.4, 270.0 and 225.9 in underweight, normal BMI, overweight and obese women, respectively. Underweight women had higher rates of the composite perinatal adverse outcome (adjusted rate ratio) [aRR] = 1.79, 95%CI = 1.32- 2.43), largely driven by increased rates of severe respiratory distress syndrome, and neonatal death (aRR = 2.81, 95%CI = 1.64-4.83). There was no evidence of elevated risk for perinatal outcomes among overweight and obese women. Conclusions In this population-based study cohort study, we found no evidence of an increased risk of adverse maternal and perinatal outcomes in overweight and obese women with twins; however, infants of underweight women are at higher risk of neonatal death and morbidity. These findings have implications for pregnancy care of women with twin pregnancies, especially those who are underweight. Funding SickKids Foundation (SKF-154852) Keywords: pre-pregnancy obesity, maternal morbidity, perinatal death