The association between serum iodine concentration in the first trimester and foetal ultrasound biometric parameters and birth size among Chinese pregnant women

PURPOSE: To investigate the relationship between first-trimester maternal serum iodine concentration (SIC) and foetal ultrasound biometric parameters as well as neonatal size at birth in Chinese pregnant women. MATERIALS AND METHODS: A birth cohort study of 1881 women from 2022 to 2024 in Zhejiang Province, China, was conducted. SIC in the first trimester was measured using inductively coupled plasma mass spectrometry. Foetal biometric parameters in mid-pregnancy were measured using ultrasound scanning techniques. Neonatal anthropometric measurements were obtained immediately after delivery. Linear regression models were used to explore the association between maternal SIC and both foetal ultrasound biometric parameters as well as birth size indicators. RESULTS: Log-transformed maternal SIC showed a significant positive association with biparietal diameter (BPD) (β = 0.102, 95% CI: 0.029, 0.174), but significant negative associations with birth length (β = -0.337, 95% CI: -0.608, -0.066) and birth weight (β = -0.091, 95% CI: -0.171, -0.012). Further sex-stratified analysis revealed that among male foetuses, SIC was significantly positively associated with BPD (β = 0.158, 95% CI: 0.053, 0.263), head circumference (HC) (β = 0.414, 95% CI: 0.074, 0.754) and abdominal circumference (AC) (β = 0.490, 95% CI: 0.111, 0.870). but negatively associated with neonatal length (β = -0.402, 95% CI: -0.742, -0.062) and birth weight (β = -0.120, 95% CI: -0.234, -0.005). These associations were attenuated and non-significant in female foetuses. Maternal age stratification showed significantly stronger positive associations between SIC and foetal BPD in women aged