Relaxin levels in amniotic fluid, extraembryonic coelomic fluid and maternal serum in early human pregnancy.

Separately identified samples of amniotic fluid and extraembryonic coelomic fluid together with maternal serum were collected from 22 women between 8 and 11 weeks of pregnancy and analysed for relaxin by immunoassay. Relaxin levels in maternal serum (median 1085 pg/ml; range 390-1259 pg/ml) were substantially higher than those in extraembryonic coelomic fluid (median 57.5 pg/ml; range 17-145 pg/ml; P < 0.0001; Mann-Whitney U-test). In turn, the levels of relaxin in coelomic fluid were higher than those in amniotic fluid (median 10 pg/ml; range 10-37 pg/ml; P < 0.0001; Mann-Whitney U-test). A linear correlation was found between relaxin levels in maternal serum and coelomic fluid (r = 0.68; P = 0.001) but there was no relation between levels in the other fluid compartments.