What hormone is NOT produced by the placenta during pregnancy?

The hormone that is not produced by the placenta during pregnancy is oxytocin. This hormone is primarily synthesized in the hypothalamus and is then transported to the posterior pituitary gland, where it is released into the bloodstream. Oxytocin plays a significant role during labor by stimulating uterine contractions and also helps with milk ejection during breastfeeding.

In contrast, human chorionic gonadotropin (hCG), relaxin, and estrogen are indeed produced by the placenta. hCG is critical for maintaining the corpus luteum in early pregnancy, which in turn, secretes progesterone essential for the maintenance of the pregnancy. Relaxin, another hormone produced by the placenta, aids in the softening of the cervix and relaxation of the pelvic ligaments in preparation for childbirth. Estrogen, which is also produced by the placenta, promotes uterine growth and mammary gland development as well as regulating various physiological changes during pregnancy. Thus, the presence of oxytocin in the list emphasizes its origin from the hypothalamus rather than the placenta.