In this study, including more than 700 IVF cycles across 3 IVF clinics, Australian fertility doctors and scientists determined that a higher number of eggs retrieved (egg yield) in an IVF treatment cycle is independently associated with more chromosomally normal embryos available for transfer. This means that more eggs can lead to more chromosomally normal embryos irrespective of the woman’s age as well as the intensity of ovarian stimulation (dose of gonadotrophins).
The presence of more chromosomally normal (euploid) embryos translates to a higher cumulative chance of a live birth after that stimulated IVF cycle. This is because chromosomally normal embryos are known to have the greatest potential for a pregnancy that will lead to a live birth and represent a clear predictive factor for IVF success.
The effect of the woman’s age
Another interesting finding of this study was that the benefit of egg yield decreased significantly with advancing female age. The study indicated that to produce 1 and 2 euploid embryos, 5 and 14 oocytes would be required at age 34. However 10 and 24 oocytes would be required at age 38. Hence, the older a woman is the more eggs have to be retrieved in order to increase the chance of obtaining an additional chromosomally normal (euploid) embryo.
Will multiple embryo transfers increase the cumulative chance of pregnancy?
The cumulative pregnancy rate refers to the chance of a pregnancy after a single stimulated IVF cycle including both fresh and frozen embryo transfers resulting from that cycle. This research helps to explain why cumulative pregnancy rates after IVF seem to improve in cycles with a higher egg yield. The more chromosomally normal embryos there are, the more transfers are possible, with an inevitably better cumulative chance of pregnancy and live birth. Chromosomally abnormal (aneuploid) embryos are unlikely to develop as pregnancies, and, if they do, sadly frequently result in miscarriage.
A number of studies published recently suggest that cumulative live IVF birth rates increase significantly with the number of eggs retrieved. This association is not evident in the initial fresh cycle of treatment, where birth rates might be even inferior when a high number of oocytes is obtained. This is most likely due to an adverse effect of intense ovarian stimulation on the receptivity of the endometrium as has been convincingly demonstrated. However, a positive association of a higher number of eggs with IVF outcome is evident when we consider the cumulative IVF birth rate from one stimulated IVF cycle.
The egg quality vs. egg quantity debate
This study also provides evidence that aiming for a higher egg yield during ovarian stimulation does not seem to compromise the quality of the eggs obtained. This has been debated for years but recently accumulated evidence suggests that a detrimental effect of intense ovarian stimulation on egg quality is unlikely. On the contrary, obtaining a higher number of eggs will probably lead to a higher number of competent eggs and, as the present study has shown, to more chromosomally normal (euploid) embryos.
Is there an optimum number of eggs collected?
While this study does provide strong evidence in the ongoing debate over the importance of egg numbers as determinants of IVF success, any attempt to propose an optimum number of egg collected needs to take into account many other parameters such as:
- Individual patient characteristics (such as age and ovarian reserve)
- The indication for treatment
- Whether one is interested in the pregnancy rate after just the fresh embryo transfer or the cumulative pregnancy rate after both fresh and frozen embryo transfers
- The number of embryos transferred (single vs. multiple embryos transferred)
- The protocols followed in the laboratory, and
- Most importantly, the patient’s wishes.
It should not be overlooked that aiming for a high number of eggs (usually more than 15) can increase the risk of ovarian hyperstimulation syndrome (OHSS), a potentially serious complication of ovarian stimulation. However, newer IVF protocols can substantially reduce this risk, allowing fertility specialists to maximize the results from a single IVF cycle and thereby reduce the financial, physical and emotional cost of fertility treatment. Increasing the oocyte yield should always be performed safely which means an individualised approach should be discussed with your fertility specialist.
Patients wishing to know more about this study, including how to increase their chance of pregnancy from IVF treatment, should speak with their local fertility specialist.