Preconception TSH Levels and Pregnancy Outcomes: a Population-based Cohort Study in 184,611 women

Summary

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 184,611women, who subsequently became pregnant, were studied. Maternal TSH was measured within six 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=7,140, 4%). Multivariable logistic regression models were used to study the association between TSH and pregnancy outcomes.

Main outcomes

Pregnancy loss, gestational age, delivery modes and birth weight.

Results

The overall incidence of adverse pregnancy outcomes was 28.6%. Compared with TSH 0.48-2.50mIU/L, TSH 2.50-4.29mIU/L was associated with spontaneous abortion (aOR 1.10, 95% 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 4.29-10mIU/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 LGA (large for gestational age) 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 non-pregnant range.

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