Association between age-specific preconception thyroid-stimulating hormone (TSH) and birth weight: a retrospective study

OBJECTIVE: Maternal thyroid function affects fetal birth weight and age is an important factor in regulating thyroid function. Thus, we aimed to explore the association between age-specific preconception thyroid-stimulating hormone (TSH) and birth weight. DESIGN: Cohort study. PARTICIPANTS: A total of 97 755 preconception Chinese women aged 20-39 years old from the National Free Preconception Checkups Project were included. SETTING: Participants were divided into four age groups: 20-25 years, 25-29 years, 30-34 years and 35-39 years. The preconception TSH levels within 6 months before pregnancy and fetal birth weight, including large for gestational age (LGA), small for gestational age (SGA) and appropriate for gestational age (AGA), were collected and analysed using restricted cubic spline regression. Logistic regression investigated the relationship between various TSH groups and birth weight. RESULTS: (1) Preconception TSH levels differed among four age groups; (2) in the 20-24 years group, preconception TSH was associated with the incidence of LGA and AGA (p