Blood biochemistry and endocrinology in the human fetus between 11 and 17 weeks of gestation.

Fetal blood was obtained in 35 normal pregnancies undergoing termination for psychosocial reasons between 11 and 17 weeks of gestation. Biochemical and endocrinological analyses were performed on each sample including concentrations of urea, creatinine, beta-microglobulin total protein, electrolytes, enzymes, alpha-fetoprotein (AFP), human chorionic gonadotrophin (HCG), thyroid stimulating hormone (TSH), thyroxin binding globulin (TBG), total thyroxin (TT4) and free thyroxin (FT4). The results were compared with values in maternal serum obtained at the same time. Fetal serum contained significantly higher concentrations of iron, beta-microglobulin, alkaline phosphatase (ALP), aspartate amniotransferase (AST), AFP, HCG and TSH and lower concentration of total protein, TBG and TT4 than maternal serum. Significant positive linear relationships were found between gestational age and the concentration of fetal serum total protein, ALP, TBG and FT4. Significant negative linear relationships were observed between gestational age and fetal serum beta-microglobulin and iron concentration. There were no significant correlations between fetal and maternal values. These data indicate that fetal blood biochemistry is not directly related to placental transfer and that the proteins and enzymes found inside the gestational sac are essentially of feto-placental origin with minimal contribution from the maternal protein metabolism. The comparison of coelomic fluid composition at 10-13 weeks with that of fetal serum at 11-17 weeks suggests that the anatomical changes in the human materno-fetal interface architecture between the early and late pregnancy periods could have a direct impact on materno-fetal transfer pathways.