Optimizing IVF outcomes in the genomics era

In order to optimize pregnancy rates during IVF cycle, we have to grow embryos in such a way to allow them to reach their full potential in-vitro. As IVF has evolved since the first live birth in 1978, culture conditions have improved and we have reached a stage where embryos can thrive to the blastocyst stage in-vitro if programmed to do so. IVF cycles typically produce multiple embryos during one cycle. Establishing which embryo has a higher potential to result in a live birth than its sibling embryos has been attempted over the last 30 years by using non-invasive and invasive techniques. Methods to choose which embryo to transfer range from basic morphology to establishing ploidy status of each embryo by biopsy.

Aneuploidy is the most common cause of implantation failure and miscarriage in human reproduction and increases with maternal age, however all maternal ages exhibit varying degrees of embryonic aneuploidy. While some non-invasive techniques have shown promise in predicting which embryos have the highest implantation potential, the only way currently to establish ploidy status of embryos in the embryology lab is to biopsy, then assay embryonic cells before transfer.

To improve IVF success, original studies derived from retrospective analysis of clinic data, or prospectively designed studies are essential and a number of fundamental biological questions pertaining to chromosome abnormalities and their relationship to IVF embryo development remain unanswered. The overall aim of this thesis was thus to provide further insight into the cytogenetic basis of early human development by pursuit of the following specific aims:

(1) To test the hypothesis that we can predict aneuploidy levels in human IVF embryos without embryo biopsy for PGS by analysis of basic morphokinetic criteria and spent media from cell free embryonic DNA, (2) to test the hypothesis that the ICSI technique may create aneuploidy in embryos, (3) to establish novel patient populations that may benefit from the use of PGS, specifically male factor infertility patients and young oocyte donors, (4) conducting a randomized controlled trial (RCT) to establish the optimal transfer strategy (fresh vs frozen) for euploid embryos in patients using their own oocytes,(5) to test the hypothesis that identifying mosaic embryos among a cohort of embryos could increase live birth rates and reduce miscarriage rates by avoiding these embryos for transfer and (6) to use the data generated from PGS/IVF cycles to provide a framework for creating realistic expectations for patients planning for their fertility future.

The conclusions of each aim were as follows: I demonstrated that poorer quality embryos showed an increased rate of aneuploidy but not large enough to predict aneuploidy for each individual embryo. Analysis of cell free DNA in spent culture media is at its early stages of development, but the study presented in this chapter using a novel WGA technique, showed that there is potential for its future use as a non-invasive PGS method.

I found that aneuploidy rates were similar in embryos generated from normal sperm whether they were created using ICSI or standard insemination using a donor oocyte model to minimize the maternal age effect (aneuploidy rates of 21% for standard IVF vs 23% for ICSI. P=>0.05 NS) concluding that the ICSI technique does not create embryonic aneuploidy.

Donor oocyte recipients (average age of donor 25) benefited from PGS in cryopreserved embryo transfer cycles by significantly increasing live birth rates per embryo from 36% with no PGS to 59% per PGS screened embryo (p=0.0008). Male factor infertility patients presenting with oligozoospermia, were shown to exhibit a significantly higher incidence of sex chromosome abnormalities in pre-implantation embryos compared to patients with normal sperm using ICSI (6.1% for oligozoospermic samples vs 1.6% for normal semen samples. P=0.0007). Both of these patient groups could benefit from offering PGS as part of their IVF cycle.

The RCT showed that freeze all cycles had higher live birth rates than fresh cycles (77% of frozen embryo transfers vs 59% of fresh embryo transfers. P=0.04).

When comparing transfer of embryos screened by NGS with those screened by aCGH, the conclusion in the relatively small subset of patients was that live birth rates for embryos screened with aCGH and NGS appear to be similar, with a 2% trend in favor of NGS (61% aCGH vs 63% NGS live born offspring per embryo transferred. P=>0.05 NS).

Lastly, the retrospective analysis of data using PGS cycles to calculate how many oocytes are required to create one euploid blastocyst depending on maternal age, resulted in a useful tool to advise patients on how many cycles of IVF they may need to complete their family.

Taken together therefore, this thesis provides fundamental insight into the chromosomal basis of early human development, introduces new referral categories for PGS and informs the practical use of IVF/PGS in the future.