The endometrium can be stimulated either naturally, by the woman’s ovarian estradiol, or artificially, by applying estradiol usually in the form of tablets or transdermal patches to obtain adequate endometrial lining thickness by ultrasound measurement. Unless a woman ovulates, the hormone progesterone is administered by the woman vaginally or by intramuscular injection to achieve optimal endometrial preparation for embryo implantation. Alternatively, following natural ovulation, the woman’s ovaries produce progesterone to accomplish this same purpose toward embryo transfer. Either natural or artificial method occurs without regard to the number of embryos planned for transfer.
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