In Vitro Fertilization (IVF) offers a pathway to parenthood for individuals and couples experiencing infertility. A frequent question arising in this process concerns the number of embryos transferred during an IVF cycle. This decision is multifaceted, influenced by various factors that aim to balance the chances of a successful pregnancy with considerations for maternal and fetal well-being.
Current Practices in Embryo Transfer
The typical number of embryos transferred during an IVF cycle has evolved. Historically, it was common to transfer multiple embryos to maximize pregnancy rates. Now, there is a global trend towards single embryo transfer (SET), particularly in cases with a favorable prognosis. This shift minimizes the risks associated with multiple pregnancies.
Modern advancements have made SET a viable and often preferred option. Professional guidelines, such as those from the American Society for Reproductive Medicine (ASRM), recommend single embryo transfer for most patients.
Factors Guiding Embryo Number Decisions
The decision regarding the number of embryos to transfer is highly individualized, considering patient-specific and clinical factors. Patient age is a primary factor, as fertility and IVF success rates decline with increasing age, particularly after 35. For instance, ASRM guidelines advise single embryo transfer for women under 38. Women aged 38-40 may have up to three untested cleavage-stage embryos or two blastocysts transferred. For those aged 41-42, up to four untested cleavage-stage embryos or three blastocysts might be considered.
Embryo quality also plays a significant role. Embryos are typically transferred at either the cleavage stage (day 2 or 3) or the blastocyst stage (day 5 or 6). Blastocyst-stage embryos generally have a higher likelihood of leading to a live birth compared to cleavage-stage embryos, as only the most robust embryos tend to reach this later developmental stage.
Medical history, including previous IVF failures or specific uterine health conditions, can also influence the number. Prior IVF cycles and clinic protocols, along with national guidelines, contribute to the personalized transfer plan.
Considerations for Single vs. Multiple Embryo Transfer
The choice between single embryo transfer (SET) and multiple embryo transfer (MET) involves weighing potential benefits against significant health implications. SET is widely recommended due to its ability to reduce the risk of multiple pregnancies, which carry substantial health risks for both the mother and the babies. Multiple pregnancies are associated with a higher incidence of complications such as preterm birth, where nearly 60% of twins and 90% of triplets are born prematurely. This can lead to low birth weight, a condition where babies weigh less than 5.5 pounds, increasing from 9% for singletons to 57% for twins.
Multiple pregnancies also elevate the mother’s risk of developing conditions like preeclampsia, gestational diabetes, pregnancy-induced hypertension, postpartum hemorrhage, and the need for a Cesarean section. While MET may offer a slightly higher chance of pregnancy per cycle, particularly for older women or those with lower quality embryos, these benefits are often offset by the increased health risks. Research indicates that the cumulative live birth rate with sequential SET (fresh followed by a frozen embryo transfer) can be comparable to a single MET cycle, but with significantly fewer risks.
Management of Remaining Embryos
After an IVF cycle, it is common to have embryos that are not transferred during the initial procedure. These remaining embryos present several options for individuals or couples. One common option is cryopreservation, or freezing, which allows for storage of viable embryos for future use. This provides the opportunity for additional embryo transfers without the need for another full IVF cycle, saving time and resources.
Another possibility is donating embryos for research purposes, which can contribute to scientific understanding in reproductive medicine. Alternatively, embryos can be donated to other individuals or couples who are also trying to build a family. This option involves legal and ethical considerations, and typically requires the donors to relinquish parental rights. Lastly, individuals may choose to discard the remaining embryos, a decision that can be emotionally complex and subject to varying personal beliefs and legal frameworks in different regions.