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

We investigated whether maternal thyroid hormone is available to the conceptus during the first trimester of pregnancy as well

B Contempré; E Jauniaux; R Calvo; D Jurkovic; S Campbell; G M de Escobar

2014

Scholarcy highlights

  • Transfer of maternal thyroxine to the human fetus near term has recently been demonstrated
  • Present evidence strongly questions concept i), and suggests a possible revision of point ii). i) Availability of maternal thyroid hormone before onset of thyroid function: Experimental studies in rats have shown that, unless the mother is hypothyroid . both T4 and T3 are available to the embryo before onset of its own thyroid function . and that the maternal transfer of T4 continues until term and protects the brain of a hypothyroid fetus from T3 deficiency
  • As recently discussed secretion of the iodothyronines is believed to start at midgestation, after development of the median eminence portal system, when there is a generalized maturation of anterior pituitary secretory cells and a concomitant sudden increase in fetal plasma T4
  • Some reports suggest that human thyroids in organ culture have the capacity to synthesize thyroxine by the lo-12th weeks of gestation but findings in vivo indicate 17 - 19 weeks as the earliest date when labeled iodothyronines are found in the fetal thyroid after administration of radioiodine to the mother
  • The preliminary results in the 8-11 weeks amniotic fluid samples agree with previous reports on the presence of T4 and reverse T3 in amniotic fluid samples obtained from 11 to 30 weeks of gestation. Concentrations of both T4 and rT3 were markedly higher in the present coelomic fluid samples than in age-paired amniotic fluids
  • Despite only representing from 0.14% up to 1.4% of the maternal T4, coelomic T4 is 10 to 100 times more elevated than the corresponding maternal free T4 at 5.8 and 11 weeks respectively
  • Transfer of T4 to the embryo could be facilitated by ITR synthesized by the yolk sac epithelium and secreted preferentially towards the embryo
  • Even in situations other than iodine deficiency, failure of the maternal thyroid gland to adapt to hormonal changes observed in normal pregnant women may prevent the increase in T4 levels which is normally observed during the first trimester of pregnancy, and affect the availability of thyroid hormone to the developing embryo

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