Detection of thyroid hormones in human embryonic cavities during the first trimester of pregnancy.

Abstract

Transfer of maternal thyroxine (T4) to the human fetus near term has recently been demonstrated. We investigated whether maternal thyroid hormone is available to the conceptus during the first trimester of pregnancy as well. Transvaginal ultrasound-guided puncture of the embryonic cavities was performed during the first trimester of pregnancy to obtain coelomic fluid between 6 and 11 weeks, and amniotic fluid between 8 and 11 weeks of pregnancy. T4 was found in coelomic fluid with mean values (+/- SEM) being 961 +/- 193 pmol T4/L (747 +/- 150 pg/mL). Concentrations increased both with gestational age and with rising maternal serum T4. Concentrations of 3,5,3'-triiodothyronine (T3) were at least 30 times lower, and those of 3,3',5'-triiodothyronine (rT3) four times higher, than coelomic fluid T4. Thyroxine and rT3 in amniotic fluid (8-11 weeks) were markedly lower than in the coelomic fluid, and T3 was undetectable. These results show that maternal thyroxine can cross the placental barrier as early as the second month of pregnancy. T4 from the coelomic fluid may reach the embryo via the yolk sac. This finding raises the possibility that the increase in maternal T4 occurring during the first trimester may be functionally important for the developing embryo, when its thyroid is not yet functioning.

Thyroid hormone action during brain development: More questions than answers

“…In humans as well as in rodents, thyroid hormones as well as their receptors are present in the fetus prior to the onset of fetal thyroid hormone A c c e p t e d M a n u s c r i p t production underscoring the relevance of maternal thyroid hormone production for fetal development (Bernal and Pekonen, 1984;Obregón et al, 1984;Contempré et al, 1993;Morreale de Escobar et al, 2004). For instance, already at week 12 of gestation both T4 and T3 can be detected in the human developing cortex but not in the serum and other fetal tissues.…”

Neonatal Hypothyroxinemia: Effects of Iodine Intake and Premature Birth

“…We obtained data for urinary I concentration in 182 samples, but reliable 24-h urine collection was not always successful. This reduced 1 PMA is the GA plus the postnatal age, in weeks. the daily I excretion data to 86 values, from 69 PT and 28 T infants.…”

“…D URING THE first half of gestation, thyroid hormone available to the fetus is predominantly of maternal origin (1). Once fetal thyroid secretion starts, fetal supplies are of mixed fetal and maternal origin.…”

“…The present study investigates the role of I intake on the thyroid function of PT infants. It reports the relationship between I intake and urinary I excretion in PT neonates at different postmenstrual ages (PMA) 1 and compares the results with those of T neonates. It also investigates whether their circulating thyroid hormone levels would reach the same values as those of T neonates once their I intakes become comparable.…”

11 Hypothyroidism in Pregnancy

“…As the fetus does not begin to produce its own TH until approximately 12 weeks' gestation, it is solely dependent on maternal T4 during early gestation [56,57]. After 12 weeks, thyroid hormone in the fetus continues to be partly supplied by the mother [58].…”