Immunocontraception outcome has focused on human chorionic gonadotropin (hCG). hCG is not necessary for fertilization, but is secreted by embryos shortly thereafter. Therefore, immunity against hCG does not prevent fertilization. However, it was found that anti-hCG antibodies prevent marmoset embryos from implanting in the endometrium of their mother's uterus. The main function of hCG is to sustain the ovarian corpus luteum during pregnancy past the time it would normally decay as part of the regular menstrual cycle. For the first 7–9 weeks in humans, the corpus luteum secretes the progesterone necessary to maintain the viability of the endometrium for pregnancy. Therefore,
Pharmacokinetics of progesterone of the menstrual cycle with LC–MS/MS are 6.7 to 22.2 ng/mL. When the unreliable method of standalone RIA has been used to measure progesterone levels with oral progesterone, far higher peak levels of 6.5 to 10.2 ng/mL, 13.8 to 19.9 ng/mL, and 32.3 to 49.8 ng/mL have been erroneously observed after single 100, 200, and 300 mg doses, respectively. In addition, progesterone levels have been inaccurately measured by RIA as remaining elevated for 12 to 24 hours. Regardless of assay method, peak levels of progesterone following a dose of oral progesterone occur after about 1 to 3 hours. The elimination