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

Whether subclinical hypothyroidism adversely impacts pregnancy outcomes is inconclusive, and limited data are available on the optimal TSH range in women planning pregnancy.

To investigate the association between maternal preconception TSH levels and pregnancy outcomes.

Population-based cohort study.

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.

Pregnancy loss, gestational age (GA), delivery modes and birthweight.

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).

Preconception TSH elevation was associated with increased risk of adverse pregnancy outcomes, even within the normal nonpregnant range.