Perinatal outcomes after fresh versus vitrified warmed blastocyst transfer: Retrospective analysis

Clinically significant differences exist between the peri-implantation and perinatal outcomes of fresh embryo transfer and frozen embryo transfer.

Kemal Ozgur, M.D., Murat Berkkanoglu, M.D., Hasan Bulut, M.D., Peter Humaidan, M.D., D.M.Sc., Kevin Coetzee, Ph.D.

Volume 104, Issue 4, Pages 899-907


To investigate the possible effect of controlled ovarian stimulation on the perinatal outcomes of assisted reproductive technology pregnancies, by comparing the outcomes from fresh ET with frozen ET (FET) with blastocysts of similar quality.

Retrospective observational study.

Private fertility center.

Seven hundred eighty-four fresh transfers and 382 vitrified-warmed double blastocyst transfers.


Main Outcome Measure(s):
Miscarriage, perinatal mortality, preterm delivery, live birth, live-birth weights, and gestational age of live births.

FET resulted in higher implantation rates (51.5% vs. 40.6%), higher live-birth rates per transfer (56.8% vs. 44.3%), and lower ectopic pregnancy rates (0.32% vs. 1.80%). FET pregnancies also had higher day 14 βhCG levels per implantation (148.2 vs. 176.2 IU/L) and higher infant birth weights (singletons Δ109.4 g, twins Δ124 g). Female infants benefitted the most in terms of birth weight. Miscarriage, premature delivery, perinatal morbidity, and live birth per pregnancy were all nonsignificantly different between fresh ET and FET.

Clinically significant differences between the peri-implantation and perinatal outcomes of fresh ET and FET suggest better endometrial receptivity and placentation in FET cycles.

  • Daniel J. Kaser, MD

    Dear authors,

    Congratulations on this important work, which nicely corroborates reports over the last several years that FET may be superior to fresh ET with regard to pregnancy rates and risk of ectopic pregnancy.

    A few questions:
    1) What was the mean estradiol for stimulated cycles?
    2) Is it possible to do a subanalysis of the FET data comparing the outcomes according to the indication for freezing (i.e., 10% freeze all for OHSS vs. 90% supernumerary freeze)? Do they behave similarly?
    3) How did you statistically treat the 42 patients that contributed multiple cycles? This is always tricky with this type of data.
    3) What about risk of placenta accreta? There have been multiple reports now indicating that the risk of accreta is higher with FET. Do you have access to obstetric outcomes like accreta for this cohort? Admittedly, a rare outcome …

    Thanks for your comments!

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