Frozen embryo transfers with zona-free blastocysts have significantly lower pregnancy and live birth rates

Trophectoderm biopsy for PGT significantly increases frozen embryo transfers (FETs) with zona-free blastocysts. Prior studies showed that zona-free blastocysts result in higher pregnancy and embryo implantation but were limited by small case numbers or multiple embryo transfer. The aim of this study is to determine whether zona-free blastocysts are associated with lower pregnancy and live birth rates in patients undergoing single blastocyst FETs. FET data from a single academic program between January 2015 and December 2021 were used for this retrospective case-control study. Inclusion criteria were women undergoing FET with day 5/6 blastocysts. Exclusion criteria were FET of ≥ 2 embryos. There were total 285 FETs with a zona-free day 5/6 blastocyst, in which 253 (88.8%) were zona-free blastocysts post PGT. Zona-intact blastocysts on day 5/6 were matched as controls based on PGT status, patient age at oocyte retrieval, and embryo quality. Clinical outcomes included positive hCG, clinical pregnancy, biochemical and clinical pregnancy loss, and live birth rates. X2 or Student t-test was used for statistical analysis. In a total of 1,983 FETs with a single blastocyst transfer, 285 (14.3%) were zona-free day 5/6 blastocyst transfers. There were no significant differences in patient age, BMI, endometrial thickness, or infertility diagnosis in the zona-free group when compared with the matched group. Zona-free blastocysts had significantly lower positive hCG, clinical pregnancy and live birth rates than the matched blastocyst group (Table 1). There were no significant differences in both biochemical and clinical loss rates between the two groups. The zona-free group also had significantly lower positive hCG, clinical pregnancy and live birth rates when compared to all 1,983 FETs (58.9% vs 67.5%, P = 0.004; 43.2% vs 50.8%, P = 0.016; and 36.8% vs 45.2%, P = 0.008).Tabled 1Table 1. Pregnancy outcomes of zona-free vs zona-intact blastocysts in FETsParametersZona-intact blastocysts (control, n = 285)Zona-free blastocysts (n = 285)P valuesPositive hCG rate (%)73.358.90.0003Clinical pregnancy rate (%)58.243.20.0003Biochemical loss rate per positive hCG (%)20.626.80.16Clinical loss rate per clinical pregnancy (%)12.714.60.63Total pregnancy loss rate per positive hCG (%)30.637.50.16Live birth rate (%)50.936.80.0007 Open table in a new tab Zona-free blastocysts in FETs yielded significantly lower pregnancy and live birth rates compared to zona-intact blastocysts in our study.