<P> Structurally, relaxin is a heterodimer of two peptide chains of 24 and 29 amino acids linked by disulfide bridges, and it appears related to insulin . </P> <P> Relaxin is produced from its prohormone, "prorelaxin", by splitting off one additional peptide chain reaction . </P> <P> In females, relaxin is produced mainly by the corpus luteum, in both pregnant and nonpregnant females; it rises to a peak within approximately 14 days of ovulation, and then declines in the absence of pregnancy, resulting in menstruation). During the first trimester of pregnancy, levels rise and additional relaxin is produced by the decidua . Relaxin's peak is reached during the 14 weeks of the first trimester and at delivery . It is known to mediate the hemodynamic changes that occur during pregnancy, such as increased cardiac output, increased renal blood flow, and increased arterial compliance . It also relaxes other pelvic ligaments . It is believed to soften the pubic symphysis . </P> <P> In males, relaxin enhances motility of sperm in semen . </P>

When does the hormone relaxin start in pregnancy