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How does the placenta take over hormone production from the corpus luteum?

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Close-up of a home pregnancy test device showing a blue plus sign in the result window, indicating a positive result for pregnancy. — pregnancy Devices for individual use at home detect pregnancy by measuring levels of the hormone human chorionic gonadotropin (hCG) in urine.

In early pregnancy, the corpus luteum is essential for producing progesterone and estrogen, which maintain the uterine lining. Following fertilization and implantation, the developing placenta begins to secrete human chorionic gonadotropin (HCG), which stimulates and maintains the activity of the corpus luteum during the first few weeks of pregnancy.123

As the pregnancy progresses, the placenta gradually develops the capacity to synthesize these hormones itself. By approximately the 70th day of pregnancy, the placenta is fully capable of producing sufficient levels of progesterone and estrogen to sustain the pregnancy independently. At this stage, the corpus luteum is no longer required and undergoes regression, eventually becoming a fibrous scar. This transition represents a highly specialized endocrine shift, ensuring the continued support of the fetus without relying on ovarian function.132