Fertility clinics determine the number of embryos to transfer per cycle based on various factors including the woman’s age, reproductive history, fertility diagnosis, embryo quality, and previous treatment outcomes. The goal is to maximize the chances of pregnancy while minimizing the risks associated with multiple pregnancies.

Considerations to balance success rates with risks include:

1. Age of the Woman: Younger women typically have higher success rates with single embryo transfers (SET) due to better embryo quality, so they may be advised to transfer fewer embryos to avoid the risks of multiple pregnancies.

2. Previous Treatment Outcomes: Women who have undergone unsuccessful IVF cycles may be recommended to transfer more embryos to enhance the chances of success.

3. Reproductive History: Women with a history of recurrent miscarriages or implantation failures may be considered for transferring multiple embryos to improve the chances of a successful pregnancy.

4. Embryo Quality: High-quality embryos have a higher chance of implantation, so transferring fewer embryos of good quality may be preferred to avoid the risks associated with multiples.

5. Ethical and Legal Guidelines: Many countries have regulations limiting the number of embryos transferred to reduce the risk of multiple pregnancies and associated complications.

6. Patient Preference: Some patients may opt for multiple embryo transfers to increase the likelihood of success, despite the higher risks involved.

By carefully considering these factors and individualizing treatment plans, fertility clinics can balance success rates with the risks of multiple pregnancies to optimize outcomes for their patients.