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When does the placenta take over much of the hormone production needed to maintain a human pregnancy?

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Detailed cross-sectional illustration of a human ovary showing the stages of follicle development, ovulation, and corpus luteum formation, with labeled structures including primordial, primary, secondary, and mature follicles, a ruptured follicle releasing an ovum, and corpus luteum and albicans. An inset at the bottom shows the ovary's location in the female reproductive system. — ovary The steps of ovulation, beginning with a dormant primordial follicle that grows and matures and is eventually released from the ovary into the fallopian tube.

In human pregnancy, the placenta gradually assumes the role of producing the estrogen and progesterone necessary to maintain the pregnancy, a function initially performed by the corpus luteum in the ovary.12

While the corpus luteum is essential during the early weeks, the placenta begins to manufacture these hormones after two months. By the 70th day of pregnancy, the placenta is fully capable of replacing the corpus luteum's function without endangering the pregnancy. This transition is so effective that human pregnancies have been known to continue undisturbed even when the corpus luteum is removed as early as the 41st day after conception.12