Influence of thyroid peroxidase antibodies on TSH levels of pregnant women and maternal-fetal complications

Introduction: During pregnancy, thyroid peroxidase (TPO) antibodies may increase the risk of developing subclinical hypothyroidism (SCH). Both conditions appear to be associated to maternal-fetal complications. The objectives of this study were to analyze if a relationship exists between TSH and TPO levels during pregnancy and the potential effects on gestational and perinatal complications, and to assess whether detectable, but not positive, TPO levels have an impact on development of gestational SCH.

Methods: A prospective study was conducted at the Leon Health Area (CAULE), where universal screening for gestational thyroid dysfunction is performed between weeks 7-13 of pregnancy. Data on TSH and TPO levels and gestational and perinatal complications were collected for all 2016 deliveries. Positive TPO antibodies were defined as values≥35IU/mL. In a previous study, a TSH level>3.72mU/L was established as the cut-off value for gestational SCH.

Results: Records corresponding to 1,980 deliveries at CAULE, 21 abortions, and 18 deliveries outside the hospital were analyzed. Of the 1,670 pregnant women screened (84.34%), 142 (8.50%) had positive TPO antibodies and their presence was associated to diagnosis of SCH (P<0.01) and to significantly higher mean TSH levels (3.51mU/L vs. 2.46mU/L, P=0.03). There were no significant differences in gestational or neonatal complications. In the group with undetectable TPO antibodies (<10lU/mL), the mean TSH levels was slightly lower than in the group with TPO values ranging from 10-35 IU/mL, but the difference was not significant (P=0.89).

Conclusion: Presence of positive TPO antibodies is associated to higher TSH levels and higher risk of gestational SCH, but does not increase the rate of maternal-fetal complications.