Frozen Embryo Transfer May Improve IVF Pregnancy Rates

Joe Barber Jr, PhD

January 09, 2013

Frozen embryo transfer (FET) may be associated with better in vitro fertilization outcomes compared with fresh embryo transfer, according to the findings of a meta-analysis.

Matheus Roque, MD, from Universitat Autonoma de Barcelona in Spain and the Origen Center for Reproductive Medicine in Belo Horizonte, Brazil, and colleagues published their findings in the January 2013 issue of Fertility and Sterility.

The authors note that the available evidence suggests that FET, at a minimum, results in similar outcomes as fresh embryo transfer. "[I]n most of the studies comparing fresh and FET, the best-quality embryos are chosen for the fresh transfer, and the results are similar between the two types of treatments," the authors write. "Therefore, if the best-quality embryos are selected for FET and the [endometrial receptivity] can be improved in these cycles, one can expect to obtain higher implantation rates, thus improving overall [assisted reproduction technique] success."

To determine whether that is, in fact, the case, the authors undertook the current systematic review and meta-analysis. They initially identified 64 articles about in vitro fertilization with fresh embryo transfer or FET from MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials. They subsequently excluded 61 articles that were not randomized controlled trials, did not match the objective of the meta-analysis, or did not inform on the outcomes of interest.

In the 3 included randomized controlled trials, which included a total of 633 cycles in women between the ages of 27 and 33 years, FET was associated with a significantly higher ongoing pregnancy rate than fresh transfer (risk ratio [RR], 1.32; 95% confidence interval [CI], 1.10 - 1.59; I 2, 0; P [for total effects] = .003).

In addition, the rate of clinical pregnancies was also higher among women who received FET (RR, 1.31; 95% CI, 1.10 - 1.56; I 2, 0; P [for total effects] = .002). A higher miscarriage rate was observed with fresh embryo transfer compared with FET, but the difference was not significant (RR, 0.83; 95% CI, 0.43 - 1.60; I 2, 0; P [for total effects] = .57).

"[T]he results of this meta-analysis suggest that there is evidence of moderate quality that the implantation, clinical, and ongoing pregnancy rates of [assisted reproduction technique] cycles may be improved by performing FET compared with fresh embryo transfer," the authors conclude. "These results may be explained by improved embryo-endometrium synchrony achieved with endometrium preparation cycles instead of [controlled ovarian hyperstimulation] cycles. The data provide a rationale for conducting further randomized clinical trials and multicenter studies to assess the consequences of [controlled ovarian hyperstimulation] on endometrial receptivity and [assisted reproduction technique] outcomes as they relate to the FET."

The authors have disclosed no relevant financial relationships.

Fertil Steril. 2013;99:156-162. Full text