Early luteal serum progesterone concentrations are higher in pregnancy cycles.

In a consecutive series of 167 patients reaching the stage of embryo transfer after in vitro fertilization and embryo transfer, 19 clinical pregnancies ensued. The serum progesterone (P) levels were significantly greater on the first and second (P less than 0.01) and third (P less than 0.05) postaspiration days for those who conceived. Higher circulating levels of P were achieved on days 1, 2, and 3 (P less than 0.05) by the daily injection of P, 50 mg in oil, given for 5 consecutive days, beginning immediately after follicle aspiration. Both pregnancy and nonpregnancy cycles demonstrated high circulating P levels, but the study implies that relatively higher levels are required for conception, and such levels can be achieved by the use of intramuscular P.