Final answer:
In the later stages of pregnancy, the placenta is the primary source of estrogen and progesterone, which are critical for maintaining pregnancy and preparing the body for labor.
Step-by-step explanation:
In the later stages of pregnancy, most of the mother's estrogen and progesterone comes from the placenta. Initially, these hormones are produced by the corpus luteum, but from weeks 12-17 of the pregnancy, as the placenta develops, it gradually takes over the role of hormone production. Hormones like estrogen and progesterone are crucial for maintaining pregnancy, preventing uterine contractions, and supporting fetal and maternal tissue growth.
Progesterone in particular has a key role in inhibiting uterine contractions to protect against preterm birth. It suppresses the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), keeping the uterus calm. As the pregnancy progresses into the third trimester, estrogen levels continue to rise while progesterone levels plateau and decrease, preparing the body for labor by making the myometrium more sensitive to contraction-inducing stimuli.