when does the hormone relaxin start in pregnancy
Relaxin In females, relaxin is produced mainly by the corpus luteum, in both pregnant [1] and nonpregnant[1] females; it rises to a peak within approximately 14 days of ovulation, and then declines in the absence of pregnancy, resulting in menstruation[citation needed]). 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.[6] It is believed to soften the pubic symphysis.
Placental expulsion As the fetal hypothalmus matures activation of the HPA axis (hypothalmic-pituitary-adrenal axis) initiates labour though two hormonal mechanisms. The end pathway of both mechanisms leads to myometrial contractions a mechanical cause of placental separation, from the shear force, contractile and involution changes in the uterus distorting the placentome.