RESEARCH QUESTION

When and how does the gradual transition of the endocrine control of early pregnancy from the corpus luteum to the placenta, termed luteoplacental shift, take place?

DESIGN

Prospective analysis of serum progesterone levels in pregnancies (n = 88) resulting from programmed frozen-thawed embryo transfer cycles in which ovulation was suppressed and no corpus luteum was present. Dydrogesterone, which does not cross-react with progesterone in immunoassay or spectrometric assay, was used for luteal phase and early pregnancy support. Progesterone, oestradiol and hCG were measured at regular intervals from before pregnancy achievement until +65 to 71 days after embryo transfer by Roche Elecsys electrochemiluminescence immunoassay (Elecsys ECLIA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Serum progesterone remained at baseline levels on first blood analysis +9 to 15 days after embryo transfer and increased only marginally independently from the type of pregnancy up to +16 to 22 days after embryo transfer. From +23 to 29 days after embryo transfer, progesterone increased non-linearly above 1.0 ng/ml and increased further throughout the first trimester with elevated levels in multiples. Oestradiol levels increased in parallel with progesterone; hCG plateaued around +37 to 43 days. Progesterone levels were significant predictors for pregnancy viability from +23 to 29 days after embryo transfer onwards with best accuracy +37 to 43 days after embryo transfer (receiver operator characteristic analysis area under the curve 0.98; 95% CI 0.94 to 1; P = 0.0009).

CONCLUSIONS

The onset of substantial progesterone production is the 7th gestational week. Progesterone increase is non-linear, depends on chorionicity and zygosity, and may have predictive potential on the outcome of pregnancies originating from frozen embryo transfer cycles.