Single Embryo Transfer Should Be Standard Practice in IVF
Elective single embryo transfer (eSET) is the recommended approach for IVF, as no clinical or embryological factor justifies routinely transferring two embryos instead of one. 1
The Evidence is Clear and Definitive
The 2024 ESHRE guideline—the most authoritative and recent guidance on this topic—provides 35 recommendations based on comprehensive literature review through May 2023. The guideline's central conclusion is unequivocal: no single clinical or embryological factor per se justifies recommending double embryo transfer (DET) over eSET. 1
Why Single Embryo Transfer Wins
Comparable or Superior Live Birth Rates
The fundamental concern that drives couples toward DET—fear of lower pregnancy rates—is not supported by the evidence when you look at the complete picture:
- Two consecutive single embryo transfers achieve higher cumulative live birth rates (45.6%) compared to one double embryo transfer (38.4%) 2
- Recent UK registry data analyzing over 71,000 treatment cycles showed that 2xSET achieved a median live birth rate of 0.47 versus 0.38 for DET 3
- Even in women with suboptimal ovarian response (≤9 oocytes), cumulative pregnancy rates were identical at 26% for both approaches 4
Dramatically Reduced Multiple Pregnancy Risk
This is where DET fails catastrophically from a morbidity and mortality standpoint:
- DET results in 30.3% multiple births versus only 1.7% with two consecutive SETs 2
- The odds of multiple births are 28-fold higher with DET compared to SET 3
- Multiple pregnancies from DET lead to substantially increased complications for both mother and babies, including preterm birth, low birthweight, and perinatal adverse outcomes 1
Maternal and Neonatal Morbidity
The complications from DET-induced multiple pregnancies are severe and well-documented:
- Preterm birth rates: 46.5% after DET versus 18.1% after two SETs 2
- Mean birth weight: 2,924g after DET versus 3,264g after two SETs 2
- DET pregnancies have 2.8-fold higher odds of preterm birth compared to SET 3
- Pregnancy loss or neonatal death rates are 2.1-fold higher with DET 3
Even singleton pregnancies resulting from DET carry higher risks than those from SET, including overall higher risk of neonatal death and complications 1
Ectopic Pregnancy Risk
The risk of ectopic pregnancy increases up to 20-fold with the number of embryos transferred, regardless of developmental stage or freezing status 1
Specific Clinical Scenarios
Absolute Contraindications to DET
DET should be avoided at all costs in these situations: 1
- Donor oocyte cycles - clearly increased pregnancy complication risks
- Donated embryos - same rationale
- Gestational carriers - same rationale
- Blastocyst transfers - higher monozygotic twin potential and high risk of multiple pregnancy complications regardless of embryo quality or cryopreservation status
Poor Prognosis Patients
This is where the nuance exists, but the recommendation remains clear:
Even in poor prognosis patients (advanced age, poor-quality embryos, multiple failed cycles), DET is NOT associated with higher cumulative live birth rates when considering each factor separately. 1
The guideline acknowledges that some clinicians consider DET in marginal cases where patients present several poor prognostic factors simultaneously. However, these patients must be counseled extensively about:
- Medical risks (short and long-term)
- Social and economic factors
- The lack of evidence supporting improved outcomes with DET
This counseling should occur through shared decision-making, but the default recommendation remains eSET 1
Age-Specific Considerations
- Women ≤39 years: 2xSET consistently provides higher live birth rates than DET or single SET 3
- Women >39 years: Results are comparable between approaches, but SET still avoids the multiple pregnancy complications 3
Cost-Effectiveness
For every live birth gained from eSET compared to DET, cost savings are $20,172 per woman (or $1,476 even when accounting for a second frozen transfer cycle). 5 Single embryo transfer is a dominant strategy—better outcomes at lower cost.
The Clinical Algorithm
Follow this decision pathway:
- Default to eSET for ALL patients as the starting recommendation
- Absolute eSET (no exceptions):
- Donor oocytes
- Donated embryos
- Gestational carriers
- Blastocyst transfers
- For poor prognosis patients (advanced age + poor embryo quality + multiple failures):
- Still recommend eSET
- If patient strongly desires DET after comprehensive counseling, document:
- Discussion of 28-fold increased multiple pregnancy risk
- 2.8-fold increased preterm birth risk
- Up to 20-fold increased ectopic pregnancy risk
- 2.1-fold increased pregnancy loss/neonatal death risk
- Understanding that cumulative live birth rates favor 2xSET over DET
- Emphasize that two consecutive SETs provide better overall outcomes
Common Pitfalls to Avoid
- Don't assume DET improves success rates - The per-cycle pregnancy rate may appear higher, but cumulative rates favor consecutive SETs
- Don't underestimate singleton risks from DET - Even when only one embryo implants after DET, those pregnancies carry higher risks than SET pregnancies
- Don't transfer two blastocysts - This is particularly high-risk due to monozygotic twinning potential
- Don't forget ectopic pregnancy counseling - This often-overlooked complication increases dramatically with DET
Quality of Life Considerations
Beyond the medical morbidity and mortality data, the guideline explicitly addresses broader impacts on families: 1
For mothers: Higher rates of safe pregnancy, vaginal delivery; lower rates of pre-eclampsia, gestational diabetes, emergency cesarean section, and preterm labor with SET
For babies: Higher rates of full-term birth, healthier childhood; lower rates of prematurity and developmental delays with SET
For families: Better parent-child interactions, less exhaustion, reduced psychological burden, fewer sick leave days, and less financial strain with SET
For society: Healthier children, healthier families, reduced financial burden with SET