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 preg nancy, but the minimal concentration of P4 necessary to sustain human pregnancy remains unclear. The aim of this study was to examine endocr ine profiles for serum P4, 17beta-estradiol (E2), and human (h) beta-C G in early pregnancy from a group of assisted reproductive technologie s (ART) patients. These subjects delivered normally but had P4 concent rations below the fifth percentile of the normal singleton pregnancy r ange from 2 weeks after ART. Normal ranges of these hormones were dete rmined from 118 consecutive ART pregnancies which resulted in singleto n births. Values below the fifth percentile (P4 < 35.9 nmol/L at 4 wee ks gestation) were considered abnormal. Eight patients who subsequentl y delivered normally, with serum P4 values below this criterion at 4 w eeks gestation, were found. They had serum P4 values at 4 weeks gestat ion 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 signif icant increase in serum P4 concentrations occurred between 7 and 11 we eks 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 conc lude that successful human pregnancy is possible with serum P4 values within the anovulatory range in early gestation and that, in individua l patients, serum P4 concentration of 2 nmol/L can be sufficient to ma intain human pregnancy.