OBJECTIVE:

Compare pregnancy rates of thawed embryo transfer between natural cycle and endometrial preparation.

MATERIALS AND METHODS:

This is a comparative, retrospective, observational study. 951 medical files where reviewed in the from January 2010 to January 2014. 75 files met with the inclusion criteria. The cycle where divided into two groups. The first group, thawed embryos where transferred during a natural cycle without any hormonal therapy. The second group, thawed embryos where transferred to a prepared endometrium with GnRH agonist and exogenous estrogen. Two embryos where transferred if the patient had two or more viable thawed embryos and one in all other cases. Variables analyzed in both groups where, age, body mass index, FSH, LH, and estrogen at the beginning of the cycle, progesterone on the day of initiating luteal support, LH and estradiol the day of embryo transfer, post-thaw embryo survival rate, number of embryos transferred, embryo quality and pregnancy rate. Groups where then divided according to the embryo quality forming a good quality cohort and a regular quality cohort. In both groups transfers during a natural cycle where compared with embryo transfer to a prepared endometrium.

RESULTS:

There was no difference observed in embryo survival or number of embryos transferred between both groups. Embryo quality was statistically better in the group with prepared endometrium. There was no statistical significant difference in pregnancy rate between the two groups. In cycles with good quality embryos there was no statistical difference in pregnancy rate when embryos where transferred during a natural cycle versus those transferred to a prepared endometrium. In cycles with regular quality embryos there was a statistical significant difference in pregnancy rate. Pregnancy rate for thawed-embryo transfer during a natural cycle was 15% and 33.3% when the transfer was to a prepared endometrium (p = 0.02).

CONCLUSION:

Endometrial preparation increases de pregnancy rate when regular quality thawed-embryos are transferred.