Preconception TSH and pregnancy outcomes: a population‐based cohort study in 184 611 women

BACKGROUND: Whether subclinical hypothyroidism adversely impacts pregnancy outcomes is inconclusive, and limited data are available on the optimal TSH range in women planning pregnancy. OBJECTIVE: To investigate the association between maternal preconception TSH levels and pregnancy outcomes. DESIGN: Population-based cohort study. METHODS: From 2010 to 2012, the free National Pre-pregnancy Checkups Project recruited 248 501 pairs of volunteer couples across China, of which 184 611 women, who subsequently became pregnant, were studied. Maternal TSH was measured within 6 months prior to conception. Participants were grouped according to TSH: 0·48-2·49 mIU/l (n = 133 232, 72%), 2·50-4·28 mIU/l (n = 44 239, 24%) and 4·29-10·0 mIU/l (n = 7140, 4%). Multivariable logistic regression models were used to study the association between TSH and pregnancy outcomes. MAIN OUTCOMES: Pregnancy loss, gestational age (GA), delivery modes and birthweight. RESULTS: The overall incidence of adverse pregnancy outcomes was 28·6%. Compared with TSH 0·48-2·50 mIU/l, TSH 2·50-4·29 mIU/l was associated with spontaneous abortion [aOR: 1·10, 95% confidence interval (CI): 1·03-1·18], preterm birth (aOR: 1·09, 95% CI: 1·04-1·15) and operative vaginal delivery (aOR: 1·15, 95% CI: 1·09-1·21), while TSH 4·29-10 mIU/l was correlated with spontaneous abortion (aOR: 1·15, 95% CI: 1·10-1·22), stillbirth (aOR: 1·58, 95% CI: 1·10-2·28), preterm birth (aOR: 1·20, 95% CI: 1·08-1·34), caesarean section (aOR: 1·15, 95% CI: 1·10-1·22) and large for gestational age (LGA) infants (aOR: 1·12, 95% CI: 1·04-1·21). CONCLUSION: Preconception TSH elevation was associated with increased risk of adverse pregnancy outcomes, even within the normal nonpregnant range.