[Thyroid functional changes of normal human fetus and newborns].

OBJECTIVE

To study the changes of the thyroid hormones level of human fetus and newborns.

METHODS

More than 71 cases of medically indicated cordocentesis have been done in 16 -36 gestational weeks in our hospital during last three years. Among them, 71 fetus who were free of diseases and their maternal thyroid function were normal were included into the study group. The blood samples were sent to analysis of thyroxine (T(4)), triiodothyroxine (T(3)), free thyroxine (FT(4)), free triiodothyroxine (FT(3)) and thyrotropin (TSH). 140 umbilical cord blood samples taken at the time of term delivery were sent to analysis of FT(4), FT(3) and TSH as a control. Normal range of different gestational weeks was calculated. Statistical analysis was done for the changes of all these thyroid hormones before 28 weeks and after.

RESULTS

All the thyroid hormones can be detected in 16 weeks of pregnancy, FT(4) already reaches the top level of adults (5.8 +/- 2.6) pmol/L and will continually increase with the increase of gestational age. There was a parallel increment of all the fetal thyroid hormone concentrations with the gestational age. The concentrations of T(4), T(3) and FT(4) have a rapidly increase after 28 weeks and have a statistically significant difference from (2.8 +/- 1.8) nmol/L, (37.2 +/- 27.2) nmol/L and (10.6 +/- 3.1) pmol/L, respectively to (5.8 +/- 2.6) nmol/L, (55.9 +/- 33.3) nmol/L, (13.0 +/- 4.5) pmol/L, respectively. TSH level of fetus was increased gradually along the gestation, reaching the up level of the adults at the 20 weeks and peaking at the birth time. While the T(3) and FT(3) keep in a lower level in gestation.

CONCLUSIONS

Fetal thyroid hormones increase with the gestational age. The diagnosis of congenital fetal thyroid hormone malfunction in the second half of the pregnancy should be monitored mainly by the T(4), FT(4) and TSH levels in different gestational age. For this consideration, to set up a reliable data for normal human fetus thyroid hormone concentrations is a very important and essential step to provide a practical guide for doctors to do intra-uterine diagnosis and treatment of associated high-risk groups. The peaking level of TSH at the birth time will surely company the changing of other thyroid hormones, so it might not be the best time to screening the congenital thyroid malfunction at the 72 hours after birth.