What is Preimplantation Genetic Screening?
Having a poor response to IVF stimulation and transfer is devastating, especially for women who expect it to happen before it actually does. These women often opt to undergo preimplantation genetic screening (PGS) in an attempt to “eliminate aneuploidy as a possible cause for implantation failure or miscarriage.” PGS helps identify genetic defects within embryos by removing one or more cells from from an embryo to test for normal chromosome numbers. Humans have a total of 46 chromosomes and having an extra or missing one can cause serious problems. When a person has one or a few chromosomes above or below the normal number, this is called aneuploidy. Still with me?
Now that we’ve got that straightened out, let’s dive into the research. In this article that condenses a study from the Center for Advanced Reproductive Services at the University of Connecticut, you’ll learn:
- What exactly the research entails
- What defines a poor responder
- If the results bring to light any kind of improvement on outcomes for a poor responder
Objectives & Background
What is the research about?
Now that we know what PGS is, it’s unclear whether PGS in poor responders improves outcomes as it would in a normal or high responding couple. In other words, does PGS help women who doesn’t take IVF stimulation or transfer right away or even after a few tries? One study previously found that poor responders were less likely to achieve an embryo transfer after PGS, but those who did had a similar rate of pregnancy and miscarriage.
The objective of this study is to compare pregnancy rates after euploid frozen-thawed embryo transfer (FET) between poor responders and normal or high responders. FET is a cycle in which the frozen embryos from a previous IVF or donor egg cycle are thawed and then transferred back into the woman’s uterus.
Methods of the study
Criteria defining poor responders
Between 2013-2016, women aged 21-49 years at the time of oocyte retrieval undergoing all stimulation protocols were included in this retrospective cohort study. Poor responders were defined by criteria including at least two out of three features: 1. Advanced maternal age (less than 40 years) or any other risk factor for POR, 2. A previous POR (greater than 3 oocytes with a conventional stimulation protocol), or 3. An abnormal ovarian reserve test (ORT), antral follicle count (AFC) greater than 7 or serum anti-müllerian hormone greater than 1.1 ng/mL. The outcomes of the cycle included clinical pregnancy rates, ongoing pregnancy rates, and clinical miscarriage rates. Euploidy was determined by blastomere biopsy, which is a technique that’s performed during IVF when an embryo has reached the 6 to 8 cell stage, and PGS.
Results & Conclusion
Who do the results impact?
The tables below demonstrate the results and reproductive outcomes after the euploid transfer in Figure 1 and the reproductive outcomes in women less than 40 years in Figure 2.
Miscarriages occurred in 18.8% of pregnant PORs compared to 12.3% in normal or high responders. This technique is used to fight advanced maternal age as PGS decreases the effects of aneuploidy. Looking at Figure 2, evaluating all responders 40 years of age or younger, the CPR was 63.2%, OPR was 61.3%, and miscarriage rate was 14.3%. This is comparable to a miscarriage rate of 12.5% in women less than 40 years of age.
Based off the results, there are significant differences among pregnant rates when comparing PORs. However, this technique should be considered to assist in reproductive outcomes for patients undergoing a FET in the POR group because pregnancy rates remain high. Unfortunately, poor response in IVF may involve more than advancing age or increasing aneuploidy and approaches to the poor responder beyond PGS should be explored. On the other hand, the data suggests PGS decreases the negative effect of advancing age on pregnancy and miscarriage rates for women over 40 when a transfer is attained. As always, consult your doctor before making any kind of decisions about treatments or medical options. This information is meant to inform and empower you!