During the first half of pregnancy, the fetus is completely dependent of maternal thyroid hormone supply and the fetal thyroid gland starts thyroid hormone secretion from about 17-19 weeks of gestational age. Conditions of maternal (sub)clinical hypothyroidism are associated with complications like hypertension, preterm birth, low birth weight, placental abruption, and fetal death. One can wonder if there are compensating mechanisms in the placenta, providing the fetus with sufficient thyroid hormone in cases of compromised thyroid supply. One study showed that total placenta deiodinase type 3 (D3) activity in pregnancies with severely hypothyroid fetuses was not significantly lower than in euthyroid controls. Two studies showed increased monocarboxylate transporter 8 (MCT8) and decreased MCT10 expression within placentae of pregnancies complicated by IUGR. As far as we know, nothing is known about possible compensating effects in placentae of mothers with subclinical hypothyroidism and the possible influence on the development of THOP.