Objective: To assess the impact of applying published fetal growth references or standards in the Chinese mainland population and to compare their ability to predict newborns small- for- gestational- age (SGA). Design: Retrospective observational study. Setting: A tertiary hospital in Shenzhen, a Chinese city with the most immigrants. Population: All pregnant women (n=106,455) who booked for prenatal care with ultrasound measurements for fetal biometry between 2012 and 2019. Methods: A fractional polynomial regression model was applied to construct Shenzhen fetal growth chart ranges for HC, BPD, AC, and FL. The differences between Shenzhen charts and published charts were quantified by calculating the Z-score. Main outcome measures: The impact of applying these published charts was quantified by calculating the proportions of fetuses with biometric measurements below the 3rd centile of these charts. The sensitivity and area under the receiver operating curves of published charts to predict neonatal SGA (birthweight <10th centile) were assessed. Results: Following selection, 169,980 scans of fetal biometry contributed by 41,032 pregnancies with reliable gestational age were analyzed. When using Hadlock references (<3rd), the proportions of small heads and short femurs were as high as 8.9% and 6.6% in late gestation, respectively. The Intergrowth-21st standards matched those of our observed curves better than other charts. When using AC<10th centile, all of these references were poor at predicting neonatal SGA. Conclusion: Applying Hadlock references could possibly misclassify a large proportion of fetuses as SGA. Conversely, applying the Intergrowth-21st standard appears to be a safe option in mainland China.

Objectives: To clarify the relationship between prepregnancy body mass index (BMI) and the phenotypes of preterm birth and evaluate the mediation effects of gestational diabetes mellitus (GDM) and preeclampsia (PE) on the relationship between prepregnancy BMI and preterm birth. Design: Prospective cohort study Setting: Shenzhen Maternity & Child Healthcare Hospital Population or Sample: 42196 singleton livebirths Methods: Prospective cohort study using the Birth Cohort in Shenzhen (BiCoS) dataset. Main Outcome Measures: Preterm birth was defined as gestational age less than 37 weeks. Results: Risks of extremely, very, and moderately preterm birth increased with BMI, and the highest risk was observed for obese women with extremely preterm birth (OR 3.43, 95% CI 1.07 –10.97). Maternal obesity was significantly associated with spontaneous preterm labor (OR 1.98; 95% CI 1.13–3.47), premature rupture of the membranes (OR 2.04; 95% CI 1.08–3.86) and medically indicated preterm birth (OR 2.05; 95% CI 1.25–3.37). GDM and PE mediated 13.41% and 36.66% of the effect of obesity on preterm birth, respectively. GDM mediated 32.80% of the effect of obesity on spontaneous preterm labor and PE mediated 64.31% of the effect of obesity on medically indicated preterm birth. Conclusions: Maternal prepregnancy obesity was associated with all phenotypes of preterm birth, and the highest risks were extremely preterm birth and medically indicated preterm birth. GDM and PE partially mediated the association between obesity and preterm birth. Funding: NSFC(81830041, 81771611); Shenzhen Science and Technology Project (JCYJ20170412140326739) KEYWORDS: obesity, prepregnancy BMI, preterm birth, phenotype, gestational diabetes mellitus, preeclampsia