Observations on the maturation of thyroid function in early fetal life

Abstract

ABSTRA CT Serum samples were obtained from 21 normal human fetuses after therapeutic abortion for psychiatric indications. Fetal crown-rump length ranged from 5.2 to 22.5 cm, corresponding to the gestational age of 65-168 days.Serum thyroxine, assayed by a modification of the Murphy-Pattee method, was identified in the second' smallest fetus examined at 78 days gestation. Thereafter it increased rapidly, maintaining a significant linear correlation with crown-rump length until term (r = 0.800, P < 0.001). Free thyroxine (FT4) also increased in a linear relation to gestational age (r = 0.908, P < 0.001), but reached term levels by 18-20 wk. Radioimmunoassayable thyroid-stimulating hormone (TSH) was detected at 78 days gestation. Levels increased rapidly with advancing gestation, so that by 16 wk almost all were within the range of term infants. After 16 wk gestation, levels were usually greater than 4.0 MU/cc, higher than that seen in normal children.No correlation was demonstrated between the serum TSH levels and total thyroxine. TSH and FT4, however, increased in a parallel manner with a significant positive correlation. This suggested that fetal TSH secretion was responsive to FT4 levels from very early in gestation, possibly as early as 11 wk.Thyroxine-binding globulin (TBG) was detected in a fetus of 78 days gestation (1.4 Ag/100 ml). Levels increased rapidly, paralleling the rise in serum thyroxine and maintaining a linear correlation with crownrump length (r = 0.864, P < 0.001). Thyroxine-binding prealbumin binding capacity (TBPA) in fetuses 14-24 wk gestation was comparable with that seen at term.When examining the distribution of tracer amounts of thyroxine-"31I (T4-"'I) between the thyroxine-binding

Biochemical investigation of foetal and neonatal thyroid function using the ACS-180SE analyser: clinical application

“…Among the remaining cases of foetal goitre one was euthyroid while the others had TSH levels above the 90th percentile (data not shown). The foetus with intrauterine growth retardation had normal serum FT 4 and TSH. sis,22 leading to an increased risk of intrauterine death, neonatal mortality and craniostenosis.P In addition, the antithyroid drugs taken by these mothers cross the placenta" and block foetal thyroid hormonogenesis, thus affecting skeletal and neurological development.!…”

“…During the second half of gestation in controls there was a significant increase in the median concentration of FT 3 [from 0·7 pmol/L (WG 22, 4 and TSH in cord blood appeared to be independent of gestational age (from 36 to 40 WG) and gender (see Table I). …”

“…Treatment of maternal Graves' disease was then adjusted and intra-amniotic administration of levothyroxine was performed.P:'? Foetal hyperthyroidism was diagnosed on the basis of increased FT 4 and FT 3 concentrations (above the 90th percentile) and undetectable TSH. Maternal antithyroid treatment was thus increased in these cases.…”

“…Thyrotrophin, free thyroxine (FT 4 ) and free tri-iodothyronine (FT3) were determined using the chemiluminescent immunoassay analyser ACS-180SE system (Bayer Diagnostics, Westwood CA, USA). Assays for free hormones on this system were of the 'labelled analogue' type."…”

“…Adult reference values for TSH, FT4 and FT 3 were 0'4-4'4mU/L, 11'5-22'7pmoI/L and 3,1-6, 5 prnol/L, respectively. The mean withinrun precision for TSH, FT 4 and FT 3 was respectively 3,3, 3·4 and 2·1% [coefficient of variation (CV)] and the mean between-run precision was respectively 3,9, 4·0 and 5·6%. The respective detection limits defined as the mean -2 standard deviations (SO) of the zero signal were 0·02 mIU /L, I·3 pmol/L and 0·5 pmol/L, TRab were detected using a radioreceptor assay (usual values < 14U/L, radioimmunoassay TRAK-assay, Brahms, Berlin, Germany).…”