Variations in serum relaxin (hRLX-2) concentrations during human pregnancy.

STUDY OBJECTIVE

To study variations in serum relaxin concentrations during normal and abnormal human pregnancy and parturition and in umbilical cord blood.

DESIGN AND PATIENTS

Diurnal variations were determined in samples collected every 2 hours for 24 hours (n = 4). Variations during pregnancy were studied in samples taken every 4th week from normal pregnant women (n = 26). Additionally samples were collected once a week from the 37th week of pregnancy and until spontaneously delivery (n = 5). Changes in relaxin during early pregnancy (gestational age: 30 to 97 days) were studied in serum from 12 normal pregnant women, 13 with spontaneous abortion and 38 with an ectopic pregnancy. Fetal serum was obtained at delivery from the umbilical vein (n = 20). All samples were analysed for relaxin by an ELISA based on human relaxin antibodies.

MAIN RESULTS

No diurnal variation in relaxin concentrations were found. In normal pregnant women relaxin concentrations increased during the first 14 weeks of pregnancy. From week 14 to 24 a gradual decrease was found and the concentrations remained constant during the last part of pregnancy. No changes in concentrations were found immediately before or during spontaneous delivery. Women with abnormal pregnancies had lower serum relaxin values than normal early pregnant women. The relaxin concentration was significantly correlated to the serum HCG concentration in early pregnancy but not to the serum HPL levels after week 28. In the umbilical vein relaxin concentrations were low.

CONCLUSION

The variation in circulating levels of relaxin during human pregnancy differs markedly from those found in other species. This suggests a different role for relaxin in human pregnancy.