Embryo Mitochondrial DNA Levels May Aid IVF Selection

Better methods of embryo selection are needed to improve in vitro fertilization (IVF) efficiency. New research shows that high quantities of mitochondrial DNA (mtDNA) may be a meaningful marker for embryo viability beyond current measures, as normal chromosome counts and high morphological grade have not guaranteed successful pregnancy of embryos.

mtDNA is a useful marker of embryonic implantation potential, independent of embryo quality and female age, according to an abstract presented at the European Society of Human Reproduction and Embryology annual meeting (Helsinki, Finland; July 3-6). The authors, from 9.baby Family and Fertility Center in Italy, say that incorporation of mtDNA copy number analysis into the routine preimplantation genetic screening (PGS) may aid selection of the euploid blastocysts with the best chances to implant.

The researchers analyzed data from 54 euploid blastocysts obtained from 26 patients (average age 35.5 years) following 29 PGS cycles. Blastocysts quality was assessed and categorized as good or bad quality based on morphology and expansion. Biopsy was performed on Day 5-6 and comprehensive chromosome screening was conducted using array comparative genomic hybridization. mtDNA content for each of 54 euploid blastocysts was quantified using real-time polymerase chain reaction (PCR) and blastocysts were categorized based on a relative mtDNA threshold value of 0.003.

The researchers found that 12 of 54 euploid blastocysts showed high mtDNA levels (22.2 percent). There were 11 successful pregnancies with healthy live births out of 43 transferred blastocysts. All pregnancies resulted from blastocysts with low mtDNA levels. No blastocysts with high mtDNA resulted in pregnancy. Overall, there was no correlation between embryo quality and mtDNA content for either the poor quality or the high quality group. Similarly, there was no statistical significant difference between female age and blastocysts’ level of mtDNA content.

In a second abstract presented at the European Society of Human Reproduction and Embryology annual meeting researchers were able to prospectively evaluate the predictive power of mtDNA quantification for the first time.

The researchers quantified mtDNA in 280 blastocysts from 143 couples, previously biopsied and found to be chromosomally normal using PGS. The study took place in a blinded manner in which mtDNA quantity was not known at the time of single embryo transfer. Embryos were biopsied at the blastocyst stage and the samples were analyzed using comprehensive chromosome analysis by next generation sequencing. The same biopsy specimens were also tested using quantitative PCR.

The researchers, funded by Reprogenetics (Livingston, N.Y.), found that 15 of the 280 blastocysts (5.4 percent) had unusually high levels of mtDNA. At the time of abstract presentation, outcome data was available for 111 of the blastocysts, transferred after PGS results were known, but before mtDNA levels were known. All transfers involved a single chromosomally normal blastocyst of good morphology. Of these, 78 (70 percent) led to ongoing pregnancies, and all (100 percent) had mtDNA levels that were normal/low. Just under one-third of blastocysts (n=33) failed to implant. Among these, seven (21 percent) had unusually high levels of mtDNA. Using mtDNA data would have led to an ongoing pregnancy rate for morphologically good, euploid blastocysts, with normal/low levels of mtDNA of 76 percent, while the ongoing pregnancy rate for morphologically good, euploid blastocysts with elevated mtDNA levels was zero.

Takeaway: mtDNA levels appear to be predictive of embryo potential. Chromosomally normal embryos with good morphology, but high mtDNA fail to result in pregnancy.