For a study, researchers sought to find a link between abnormal thyroid function tests and the risk of prenatal hypertension and pre-eclampsia. They searched MEDLINE (Ovid), Embase, Scopus, and the Cochrane Database of Systematic Reviews for prospective cohort studies with data on maternal concentrations of thyroid-stimulating hormone (TSH), free thyroxine (FT4), thyroid peroxidase (TPO) antibodies, individually or in combination, as well as gestational hypertension, pre-eclampsia, or both, from inception to Dec 27, 2019, for prospective cohort studies. Investigators extended an open invitation to study authors to join the Consortium on Thyroid and Pregnancy and contribute data on individual participants. Participants with pre-existing thyroid dysfunction, multifetal pregnancy, or drugs that impacted thyroid function were excluded. Documented gestational hypertension and pre-eclampsia were the primary outcomes. Individual participant data were analyzed using logistic mixed-effects regression models that accounted for maternal age, BMI, smoking, parity, ethnicity, and gestational age at blood collection. They found 1,539 published studies, 33 satisfied the inclusion criteria, and 19 were included after the authors agreed to participate. The study included 46,528 pregnant women, with 39,826 (85.6%) having enough data (TSH and FT4 concentrations and TPO antibody status) to be categorized as having normal thyroid function. About 1,275 (3.2%) of the women had subclinical hypothyroidism, 933 (2.3%) had isolated hypothyroxinemia, 619 (1.6%) had preclinical hyperthyroidism, and 337 (0.8%) had overt hyperthyroidism. Subclinical hypothyroidism was linked to a higher risk of pre-eclampsia than euthyroidism (2.1% vs. 3.6%; OR 153 [95% CI 1.09–2.15]). TPO antibody positivity, isolated hypothyroxinemia, or subclinical hyperthyroidism were not linked to pregnant hypertension or pre-eclampsia. A greater and lower TSH concentration was linked to a higher risk of pre-eclampsia in continuous analysis (P=0.0001). The concentrations of FT4 were not linked to the outcomes studied. Subclinical hypothyroidism during pregnancy was linked to a higher incidence of pre-eclampsia than euthyroidism. TSH had a U-shaped relationship with pre-eclampsia. The outcomes add to the body of information on the risk of unfavorable maternal and fetal outcomes of thyroid dysfunction during pregnancy by quantifying the risks of prenatal hypertension or pre-eclampsia in women with thyroid function test abnormalities. The outcomes could have consequences for determining the best treatment target for pregnant women taking levothyroxine, which would need to be tested in future interventional trials.
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