Mode of conception does not appear to influence fetal growth-to-placental weight ratios throughout gestation. In addition, findings in animal models may not always translate into human studies of infertility treatment outcomes.

also plotted by gestational week to determine a significant increase in levels which would suggest the luteo-placental shift has occurred. The graphical interpretation shows the steepest slope between weeks 5-6 (m¼4.54) followed by weeks 6-7 (m¼4.34). The average estrogen levels were also graphically evaluated with the greatest rise between week 6-7 (m¼303.8). CONCLUSIONS:Frozen embryo transfer provides an excellent model for the assessment of the luteal-placental shift, as pregnant patients produce essentially no endogenous E2 or P4 until that time. By evaluating both absolute E2 and P4 levels as well as the rate of rise, we can surmise the timing of the actual shift. These data suggest that the actual shift occurs around 7 weeks' gestation, and that patients undergoing FET should continue to receive estradiol replacement until at least 7 weeks' gestational age and progesterone replacement until at least 8-9 weeks' gestational age.

No abstract