Pregnancy Rates in Women Undergoing IVF With Fresh vs Frozen Embryos

Embryo selection for IVF light micrograph
Embryo selection for IVF light micrograph
Study evaluated the difference in the rate of ongoing pregnancy or live birth between frozen embryo transfer and fresh embryo transfer in women without polycystic ovary syndrome who were undergoing IVF.

Rates of ongoing pregnancy in women receiving in vitro fertilization (IVF) transfers of fresh vs frozen embryos may not differ, according to a study published in the New England Journal of Medicine.

Researchers conducted a single-center, randomized controlled trial in Ho Chi Minh City, Vietnam ( identifier: NCT02471573), to determine the effectiveness of transferring fresh vs frozen embryos in infertile women undergoing IVF who have not been diagnosed with polycystic ovary syndrome.

A total of 782 women were recruited and were randomly assigned 1:1 into 2 groups: the fresh embryo group (n=391) and the frozen embryo group (n=391). The primary outcome of the study was ongoing pregnancy after the first transfer of embryos via a detectable heartbeat at 12 weeks of gestation.

Study results found that 142 of 391 women in the frozen embryo group and 135 of 391 women in the fresh embryo group achieved an ongoing pregnancy after the first cycle, with a between-group difference of 1.8 percentage points (95% CI, −5.2 to 8.7 percentage points; risk ratio [RR], 1.05; 95% CI, 0.87-1.27; P =.65). The median time to conception in the fresh embryo group was 1.4 months shorter.

Although there were many secondary outcomes measured, the live birth rate did not significantly differ between the 2 groups, with live births occurring in 33.8% and 31.5% of women who received frozen and fresh embryos, respectively, for a between-group difference of 2.3 percentage points (95% CI, −4.5 to 9.1; RR, 1.07; 95% CI, 0.88-1.31; P =.54.

Women in the frozen embryo and fresh embryo groups who completed 12 months of follow-up were found to have live birth rates of 48.8% and 47.3%, respectively (RR, 1.03; 95% CI, 0.89-1.19; P =.72).

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Limitations of this study include it being a single center study in 1 country with a maximum transfer of 2 embryos.

Researchers concluded that there were no significant differences in ongoing pregnancy rates in women without polycystic ovary syndrome who underwent fresh or frozen embryo IVF transfers. In addition, there were no differences in live birth rates between groups after the first transfer cycle or at the 12-month rate of ongoing pregnancies. Clinicians can use these data to guide individuals in family planning and preferred timing of transfers in women undergoing IVF.


Vuong LN, Dang VQ, Ho TM, et al. IVF transfer of fresh or frozen embryos in women without polycystic ovaries. N Engl J Med. 2018;378:137-147.