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The hormone that maintains pregnancy later is progesterone. In early gestation, hCG from the developing placenta rescues the corpus luteum, which then secretes progesterone to support the endometrium. As the placenta matures, it takes over progesterone production, keeping the uterine lining secretory and suppressing uterine contractions to maintain pregnancy. Estrogen supports uterine growth and blood flow, and relaxin assists remodeling, but progesterone is the main hormone ensuring continued pregnancy in the later stages.