Does blastocyst mitochondrial DNA content affect miscarriage rate in patients undergoing single euploid frozen embryo transfer?

To determine whether the blastocyst mitochondrial DNA (mtDNA) content is related to the miscarriage rate in patients undergoing single euploid frozen embryo transfer (SEFET). A total of 355 single euploid frozen embryo transfer cycles were studied retrospectively between April 2017 and December 2018. A trophectoderm biopsy was performed on day 5/6 blastocysts. Post next-generation sequencing (NGS), the mtDNA content was calculated as the ratio of mitochondrial DNA over nuclear DNA, and the association between blastocyst mtDNA content and miscarriage rate was evaluated. Three hundred fifty-five euploid blastocysts were selected for SEFET in 314 patients with an average age of 33.7 ± 5.6 years; 255 were biopsied on day 5 (71.8%) and 100 on day 6 (28.2%). Frozen embryo transfer (FET) was performed either in a hormone replacement therapy (HRT) cycle (71.8%; n = 255) or in a natural cycle (NC) (28.2%; n = 100). A pregnancy rate of 66.2% (235/355) was obtained with clinical pregnancy and miscarriage rates of 52.4% (n = 186) and 5.6% (n = 20), respectively. There was no significant difference neither between the blastocyst mtDNA content of pregnant and nonpregnant patients (27.7 ± 9.2 vs. 29.4 ± 8.6, P = 0.095) nor between patients with a clinical pregnancy and miscarriage (30.5 ± 9.3 vs. 27.3 ± 9.2, P = 0.136). Multivariate logistic regression analysis showed the same nonsignificant relationship, except for the miscarriage rate and BMI (OR 1.149, 95% CI 1.03-1.28; P = 0.012). Mitochondrial DNA content is unable to predict the miscarriage of implanted human euploid blastocysts.