Thyroid peroxidase antibody titers, thyroid function, and iodine nutrition status of pregnant normotensive and preeclamptic women in Eastern Cape South Africa

Autoimmune thyroid disease, one of the main risk factors for hypothyroidism, is associated with adverse pregnancy outcomes. The burden of autoimmune thyroid disease in pregnancy and its association with thyroid function among normotensive pregnant women and pregnant women with hypertension in South Africa are not known.

In the rural Eastern Cape of South Africa, pregnant women in the third trimester of pregnancy have thyroid peroxidase antibody titers that show negative thyroid autoimmune status. Insufficient iodine intake, other than thyroid autoimmune disease, seems to be the underlying cause of the lower free triiodothyronine and free thyroxine levels observed among women with preeclampsia.

This study aimed to establish the magnitude of thyroid peroxidase autoantibodies in pregnancy in the Eastern Cape of South Africa and its relationship with iodine nutrition status and preeclampsia. Study design: Overall, 60 randomly selected normotensive pregnant controls at term and 120 pregnant participants with preeclampsia in the third trimester of pregnancy going to the Mthatha Regional Hospital and the Nelson Mandela Academic Hospital in the Eastern Cape Province who had complete data on thyroid peroxidase antibody titers, urinary iodine concentrations, serum thyroid-stimulating hormones, and free triiodothyronine, free thyroxine, and thyroglobulin levels were enrolled in this unmatched case-control study.

The cases and controls had similar mean chronological age (23.8 vs 24.0 years), body mass index (29.4 vs 28.8 kg/m2), and median parity (both 1) (P>.05). The controls had a higher mean gestational age than participants with preeclampsia (38.5 vs 33.7 weeks, respectively; P<.001). Both participants with preeclampsia and normotensive participants had median thyroid peroxidase antibody levels consistent with a negative thyroid autoimmune status. Participants with preeclampsia had higher but nonstatistically significant median thyroid peroxidase antibody (2.14 vs 1.77 IU/L), thyroglobulin (25.9 vs 21.3 µg/L), and thyroid-stimulating hormone (2.4 vs 2.3 mIU/L) levels (P>.05) and significantly lower median urinary iodine concentration (123.4 vs 188.6 µg/L), free thyroxine (13.2 vs 14.1 pmol/L), and free triiodothyronine (4.3 vs 4.6 pmol/L) levels (P<.05) than normotensive controls. Thyroid peroxidase antibodies were positively correlated with thyroglobulin, urinary iodine concentration, and thyroid-stimulating hormone.