Final answer:
Pregnancy is maintained by the collaborative action of hormones such as estrogen, progesterone, and hCG initially from the corpus luteum and later from the placenta, alongside contributions from the anterior pituitary gland that support fetal development and prepare the maternal body for childbirth.
Step-by-step explanation:
During pregnancy, specific hormones play crucial roles in maintaining the pregnancy and preparing for childbirth. Estrogen, progesterone, and human chorionic gonadotropin (hCG) are among these central hormones. Estrogen and progesterone are initially produced by the corpus luteum and later by the placenta, with estrogen levels climbing throughout pregnancy to support progression and progesterone facilitating the nourishment of the early blastocyst. The anterior pituitary gland also contributes by increasing levels of thyrotropin, prolactin, and ACTH, which stimulate thyroid hormone production, mammary gland enlargement, and maternal cortisol secretion, respectively. These hormonal changes support the fetus and prepare the mother's body for delivery and postnatal care. The placenta takes over this role from weeks 12-17 of the pregnancy to further support fetal growth and prepare for childbirth, which is indicated by increasing estrogen levels and hormonal support for maternal physiological changes.