Pregnancy outcomes in women with severe hypothyroidism

Hypothyroidism during pregnancy has been associated with adverse obstetrical outcomes. Most studies have focused on subjects with a mild or subclinical disorder. The aims of the present study were to determine the relative rate of severe thyroid dysfunction among pregnant women with hypothyroidism, identify related factors and analyse the impact on pregnancy outcomes.

A retrospective case series design was employed.

The study group included 101 pregnant women (103 pregnancies) with an antenatal serum TSH level >20.0 mIU/l identified from the 2009-2010 computerised database of a health maintenance organisation. Data were collected from the medical records. Pregnancy outcomes were compared with those of a control group of 205 euthyroid pregnant women during the same period.

The study group accounted for 1.04% of all insured pregnant women with recorded hypothyroidism during the study period. Most cases had an autoimmune aetiology. All women were treated with levothyroxine (L-T₄) during pregnancy. Maximum serum TSH level measured was 20.11-150 mIU/l (median 32.95 mIU/l) and median serum TSH level 0.36-75.17 mIU/l (median 7.44 mIU/l). The mean duration of hypothyroidism during pregnancy was 21.2 ± 13.2 weeks (median 18.5 weeks); in 36 cases (34.9%), all TSH levels during pregnancy were elevated. Adverse pregnancy outcomes included abortions in 7.8% of the cases, premature deliveries in 2.9% and other complications in 14.6%, with no statistically significant differences from the control group. Median serum TSH level during pregnancy was positively correlated with the rate of abortions+premature deliveries and rate of all pregnancy-related complications (P<0.05).

Abortions and premature deliveries occur infrequently in women with severe hypothyroidism. Intense follow-up and L-T₄ treatment may improve pregnancy outcomes even when target TSH levels are not reached.