Pregnant women with first-trimester thyroid-stimulating hormone levels of 2.5 mIU/L to 5 mIU/L had increased risks for adverse neonatal outcomes such as perinatal loss, miscarriage and premature birth compared with women with lower levels of the hormone, a new study, published in the journal Clinical Endocrinology, shows.

To determine associations between fetal and maternal complications with first trimester maternal TSH values, Marta Hernández, MD, of the endocrinology and nutrition department at the Hospital Universitari Arnau de Vilanova in Spain, and colleagues evaluated data on 1,981 women (mean age, 30.12 years).

The participants underwent screening for thyroid function at the same hospital. The screening was performed between weeks 9 and 12 of gestation. Median TSH level was 1.72 mIU/L; 26.9% had TSH levels greater than 2.5 mIU/L and 3.2% had levels greater than 5 mIU/L.

Median TSH levels were higher in participants with a miscarriage compared with those without a miscarriage (1.97 mIU/L vs. 1.71 mIU/L;= .009). Participants with preeclampsia also had higher median TSH levels compared with those without preeclampsia (2.19 mIU/L vs. 1.71 mIU/L; = .027). First trimester maternal TSH levels were not correlated with infant weight.

Compared with participants with TSH levels less than 2.5 mIU/L, those with levels of 2.5 mIU/L to 5 mIU/L had a higher risk for perinatal loss. After adjustment for mother’s age, compared with participants with TSH levels less than 2.5 mIU/L, those with levels of 2.5 mIU/L to 5 mIU/L had greater risks for perinatal loss, miscarriage and premature birth.

“Our results are in agreement with previous studies that have demonstrated an association between the value of TSH during the first trimester of pregnancy and the incidence of maternal and fetal complications,” the authors wrote.

“Our data support that higher levels of TSH within the reference normal concentrations during the first trimester are associated with higher risk of adverse obstetric outcomes, but the single measurement of crude TSH has no individual predictive value,” the authors concluded.