Final answer:
Relaxin, a hormone secreted initially by the corpus luteum and then by the placenta, facilitates the relaxation and increased elasticity of the pelvic ligaments and pubic symphysis to prepare the body for childbirth and cervix dilation.
Step-by-step explanation:
Relaxation of the pelvic ligaments and pubic symphysis during pregnancy is promoted by the hormone relaxin, which is secreted by the corpus luteum and later by the placenta.
Relaxin increases the elasticity of the symphysis pubis joint and pelvic ligaments to facilitate the growth of the fetus and prepare for childbirth. In addition to causing these changes in the pelvis, relaxin also helps to dilate the cervix during labor.