Is the luteo-placental shift a myth? Analysis of low progesterone levels in successful art pregnancies.

Progesterone (P4) is considered vital to the maintenance of human pregnancy, but the minimal concentration of P4 necessary to sustain human pregnancy remains unclear. The aim of this study was to examine endocrine profiles for serum P4, 17 beta-estradiol (E2), and human (h) beta-CG in early pregnancy from a group of assisted reproductive technologies (ART) patients. These subjects delivered normally but had P4 concentrations below the fifth percentile of the normal singleton pregnancy range from 2 weeks after ART. Normal ranges of these hormones were determined from 118 consecutive ART pregnancies which resulted in singleton births. Values below the fifth percentile (P4 < 35.9 nmol/L at 4 weeks gestation) were considered abnormal. Eight patients who subsequently delivered normally, with serum P4 values below this criterion at 4 weeks gestation, were found. They had serum P4 values at 4 weeks gestation ranging from 1.9-29.9 nmol/L, and their mean P4 values at 5 weeks (30.2 +/- 9.2 nmol/L; mean +/- SE) and 6 weeks gestation (48.0 +/- 10.2 nmol/L) remained below the fifth percentile. No statistically significant increase in serum P4 concentrations occurred between 7 and 11 weeks gestation in these women. Their mean E2 value in serum at 4 weeks gestation (382 +/- 73 pmol/L) was also below the fifth percentile but their mean beta-hCG concentration was within the normal range. We conclude that successful human pregnancy is possible with serum P4 values within the anovulatory range in early gestation and that, in individual patients, serum P4 concentration of 2 nmol/L can be sufficient to maintain human pregnancy.