Gonadotrophins during second trimester of pregnancy: I. LH and hCG levels in maternal serum and amniotic fluid and their relationship to the sex of the foetus.

Luteinizing hormone and chorionic gonadotrophin levels were selectively measured by using radioimmunoassays in 98 maternal sera and 116 amniotic fluid samples obtained 10--20 weeks of pregnancy. Levels of hCG in serum were clearly high during 10--14 weeks and thereafter declined gradually. In contrast, serum concentrations of LH during 10--20 weeks were either unmeasurable (less than 1 ng/ml) or lower than those observed during the luteal phase of the menstrual cycle suggesting a decreased responsiveness of pituitary and/or a higher clearance rate for LH during this period of pregnancy. Neither LH nor hCG levels in maternal sera showed significant differences between male and female foetus bearers. A striking similarity was observed between maternal serum and amniotic fluid hCG patterns, despite hCG levels in maternal sera being always higher (1.5--26.9 fold). On the other hand amniotic fluid concentrations of LH became elevated following 12 weeks of gestation while maternal serum LH continued to be at low levels until 20 weeks. Furthermore a sexual dichotomy was observed in amniotic fluid LH concentrations but not in hCG levels during 14--20 weeks of pregnancy, with significantly lower LH levels in male foetus bearers than in female foetus bearers. Of interest is the clear demarcation in LH levels at 16 weeks of gestation. This sequential pattern of change in the concentrations of amniotic fluid LH is similar to those patterns reported by other investigators for foetal serum and pituitary LH during 10--20 weeks of gestation suggesting that the foetus may be the source of the increased levels of LH in amniotic fluid following 12 weeks of pregnancy.