In Vitro Fertilization (IVF) is a process where an egg is combined with sperm outside the body. After fertilization, the resulting embryos are monitored before embryo transfer (ET) into the patient’s uterus. The decision on the number of embryos to transfer aims to maximize pregnancy success while minimizing health risks associated with multiple gestations. This choice is guided by current medical standards and is highly personalized based on the patient’s clinical profile. Practice has shifted toward safety, favoring singleton live births over high-number transfers.
Current Guidelines for Embryo Transfer
The current standard of care promotes elective Single Embryo Transfer (eSET) for many patients. This approach reduces the incidence of multiple pregnancies, which carry higher risks for both mother and child. For women under 35 with a favorable prognosis, such as those with good quality embryos or those in their first cycle, eSET is the recommended treatment plan. This age group often has the highest success rates per embryo, making a single transfer a safe and effective strategy.
As a patient’s age increases, guidelines allow for the transfer of a higher number of embryos to offset the natural decline in implantation potential. For instance, women aged 38 to 40 are advised not to exceed two blastocysts or three cleavage-stage embryos if the embryos are untested. The maximum number increases slightly for women aged 41 to 42, often up to three blastocysts, reflecting the lower expected success rate per embryo. These age-based limits provide a framework for clinics to minimize health complications associated with multiple births.
Individualized Factors Determining Transfer Number
While age provides a general framework, the final number of embryos transferred is customized by specific clinical and embryological factors. Embryo quality is a primary determinant, graded based on morphology and developmental stage. A high-quality blastocyst (Day 5 or Day 6 embryo) has a higher implantation potential than a lower-graded embryo, making it a strong candidate for eSET.
The patient’s history of previous IVF attempts also modifies standard guidelines. Patients with multiple failed cycles despite good-quality embryos may be candidates for a double embryo transfer (DET) to increase success odds. Preimplantation Genetic Testing (PGT) is also important; if an embryo is confirmed chromosomally normal (euploid), only one is transferred regardless of age due to the high implantation rate. Other considerations include uterine factors, such as the condition of the endometrium, and coexisting medical conditions that make multiple pregnancy hazardous.
Clinical Outcomes of Multiple Embryo Transfer
The adoption of eSET is driven by the increased health risks associated with multiple gestations resulting from transferring two or more embryos. A twin pregnancy carries a higher probability of adverse outcomes for both mother and babies compared to a singleton pregnancy. The most common complication is preterm birth, with over 50% of twins born prematurely, often leading to prolonged stays in the Neonatal Intensive Care Unit (NICU).
Prematurity often results in low birth weight, linked to a higher risk of long-term health issues, including respiratory distress syndrome and neurodevelopmental delays. For the mother, carrying multiples elevates the risk of severe complications such as preeclampsia and gestational diabetes. The need for a Cesarean section is also higher in twin pregnancies. Clinics focus on achieving a single, healthy pregnancy through eSET, favoring the lowest possible risk profile.