Which hormone is involved in the muscular contraction of the uterus at the time of birth?

Oxytocin is the hormone that plays a crucial role in stimulating muscular contractions of the uterus during childbirth. This powerful hormone is produced in the hypothalamus and released by the posterior pituitary gland. Oxytocin is responsible for increasing the frequency and intensity of contractions, aiding in the progression of labor.

During labor, the pressure of the baby's head against the cervix triggers further release of oxytocin in a positive feedback loop, enhancing uterine contractions. This mechanism ensures an effective birth process.

The other hormones listed, such as progesterone, primarily help maintain pregnancy and suppress uterine contractions during the gestational period. Follicle stimulating hormone (FSH) plays a role in the reproductive cycle but is not involved in uterine contractions at birth. Relaxin is involved in preparing the body for childbirth but does not directly stimulate uterine contractions like oxytocin does.