Why Some Infertility Specialists Prefer Double-Embryo Transfer
Single embryo transfer (SET) should be the standard practice in IVF/ICSI, as double-embryo transfer (DET) does not improve cumulative live birth rates but dramatically increases multiple pregnancy complications without meaningful benefit to maternal or neonatal outcomes 1.
The Evidence Against Routine DET
The 2024 ESHRE guideline—the most authoritative and recent guidance on this topic—found no clear indication in any single prognostic factor to favor DET over SET 1. The cumulative live birth rate (CLBR) with SET is not inferior to DET when considering the full treatment cycle including frozen embryo transfers 1. This means that while DET may produce a higher pregnancy rate in a single fresh cycle, the overall chance of taking home a baby is equivalent when SET patients use their frozen embryos in subsequent cycles.
Why Some Specialists Still Choose DET
Despite clear evidence, some specialists opt for DET in specific clinical scenarios:
Poor Prognosis Patients
Specialists sometimes transfer two embryos when patients present multiple poor prognostic factors simultaneously, including 1:
- Advanced maternal age (particularly ≥38 years)
- Poor-quality embryos
- Multiple previous failed IVF cycles (≥2 unsuccessful attempts)
However, even in these marginal cases, DET does not improve cumulative live birth rates 1. The practice persists largely due to:
- Patient pressure and anxiety after repeated failures
- Perceived psychological benefit of "maximizing chances" in a single cycle
- Financial constraints limiting access to multiple cycles
The Clinical Dilemma
The fundamental reason DET persists is a long-standing but flawed clinical assumption: DET produces higher clinical pregnancy rates per fresh transfer (49.2% vs 45.1%) 2. This creates pressure from both patients and clinicians who focus on immediate pregnancy rates rather than cumulative outcomes and safety 3, 4.
Notably, 40-50% of patients refuse SET even after counseling about multiple pregnancy risks, preferring the perceived higher success rate of DET 4.
The Serious Risks of DET
When specialists choose DET, they expose patients to substantial harms:
Maternal Complications
- Pre-eclampsia
- Gestational diabetes
- Emergency cesarean section
- Preterm labor
- Up to 20-fold increased risk of ectopic pregnancy 1
Neonatal Complications
- 33% multiple birth rate with DET vs 0.8% with SET 5
- Prematurity (46.5% vs 18.1%) 2
- Lower birth weight (2924g vs 3264g) 2
- Increased neonatal death risk
- Developmental delays
Critical Caveat
Even singleton pregnancies after DET carry higher complication risks compared to singletons after SET 1. This means the harm extends beyond just multiple gestations.
Absolute Contraindications to DET
DET should be avoided at all costs in 1:
- Donor oocyte cycles
- Donated embryo transfers
- Gestational carrier arrangements
- Blastocyst transfers (due to higher monozygotic twinning risk)
The Correct Approach
For patients aged 35-37 years: SET is superior for both first and second transfer cycles 6.
For patients aged 38-42 years: While some data suggest DET may improve live birth rates in the second cycle after a failed first attempt 6, this must be weighed against the substantial maternal and neonatal risks. The decision requires comprehensive shared decision-making that prioritizes safety over marginal pregnancy rate improvements 1.
Mandatory Counseling Before DET
If DET is considered, patients must understand 1:
- Medical risks (short and long-term)
- Social and economic burden of multiple births
- Psychological strain on families
- That cumulative live birth rates are equivalent with SET
- That singleton pregnancies after DET still carry increased risks
Common Pitfalls to Avoid
- Focusing on per-cycle pregnancy rates rather than cumulative live birth rates and safety outcomes
- Yielding to patient pressure without thorough counseling about multiple pregnancy complications
- Assuming poor prognosis justifies DET when evidence shows no cumulative benefit
- Transferring two blastocysts under any circumstances
- Using DET in donor cycles or with gestational carriers
The persistence of DET reflects a gap between evidence and practice driven by patient anxiety, financial pressures, and outdated clinical paradigms rather than superior outcomes 3.