Relaxin in amniotic fluid and in maternal serum during pregnancy

Relaxin was measured in serum and amniotic fluid of 136 pregnant women between the 12th and 38th gestational week by means of a new human relaxin-RIA. The pregnancies consisted of 111 pathology-free single fetuses, 10 with rhesus incompatibility, 7 with chromosomal aberration and 8 with sonographic diagnosed abnormalities. Relaxin could be detected in all samples tested the levels being ten times lower in amniotic fluid compared to serum. Serum relaxin levels showed a slight but not statistically significant decrease with increasing gestational age, in amniotic fluid relaxin values were consistent over the course of pregnancy. The ratio of amniotic fluid to serum relaxin displayed a statistically significant increase from the 12th to 23th week of pregnancy. Individual courses of relaxin concentrations in amniotic fluid revealed only low intra-individual variations but distinct inter-individual differences.