Single vs Double Embryo Transfer: SET vs DET Explained

Bottom line up front: For most patients — especially those under 38 with good-quality blastocysts — single embryo transfer (SET) is the recommended approach. The per-transfer pregnancy rate is slightly lower than double embryo transfer (DET), but the cumulative success rate across two single transfers is comparable to one double transfer, with dramatically lower twin pregnancy risk. Twins carry serious health risks that most patients underestimate.

The Numbers

Metric	Single Embryo Transfer (SET)	Double Embryo Transfer (DET)
Pregnancy rate per transfer (under 37)	40–50%	50–60%
Twin pregnancy rate	1–2% (identical twins only)	25–35%
Cumulative rate after 2 transfers	65–75%	50–60% (one transfer)
Preterm birth risk (singletons)	~10%	N/A
Preterm birth risk (twins)	N/A	~60%
NICU admission rate (singletons)	~8%	N/A
NICU admission rate (twins)	N/A	~40%

The key insight: DET increases the per-transfer pregnancy rate by roughly 10 percentage points — but it increases the twin rate from near-zero to 25–35%. The marginal improvement in pregnancy rates is modest; the increase in twin risk is dramatic.

Why Twin Pregnancies Are Riskier Than You Think

Many patients see twins as a desirable outcome — "two for the price of one." This is understandable but medically misguided. Twin pregnancies, even with two healthy embryos, carry substantially elevated risks for both mother and babies:

Preterm birth: Approximately 60% of twins are born before 37 weeks, compared to about 10% of singletons. Premature babies face higher rates of respiratory problems, feeding difficulties, and long-term developmental concerns.
Low birth weight: Average twin birth weight is significantly lower than singletons. Low birth weight increases neonatal complications and can have long-term health implications.
Pre-eclampsia: Twin pregnancies double the risk of pre-eclampsia — a potentially life-threatening condition involving dangerously high blood pressure.
Gestational diabetes: Risk increases with twin pregnancy due to greater metabolic demand.
Caesarean delivery: The C-section rate for twins is approximately 75%, compared to about 30% for singletons.
NICU stays: Around 40% of twins require NICU admission, compared to about 8% of singletons. NICU costs can be devastating — often $3,000–$10,000 per day in the US.

⚠️ The Financial Reality of Twins

Patients often choose DET to save money on a second transfer cycle. But the potential costs of a twin pregnancy — extended bed rest, lost income, preterm delivery, NICU stays, and higher childcare costs — can dwarf the savings. In the US, the average additional cost of a twin vs singleton delivery is estimated at $100,000–$200,000 when NICU stays are included.

When DET Might Be Appropriate

Double embryo transfer is not categorically wrong — there are situations where it may be reasonable:

Age 38 or older

Implantation rates decline with age and embryo quality. For patients 38+ without PGT-A tested embryos, transferring two embryos may be reasonable because the twin rate is lower (each embryo has a lower individual implantation chance).

Repeated implantation failure

If you have had two or more failed single embryo transfers with good-quality embryos, your doctor may recommend DET for the next attempt.

Limited embryos available

If you have only 2–3 embryos total and your age or prognosis is a concern, maximising the chance per transfer may outweigh the twin risk — but this is a case-by-case decision.

Lower-quality embryos

If the available embryos are graded lower quality (day 3 embryos rather than blastocysts, or lower morphological grades), transferring two may be appropriate because each has a lower individual implantation probability.

The PGT-A Factor

Pre-implantation genetic testing (PGT-A) changes the equation significantly. When embryos have been tested and confirmed euploid (chromosomally normal), each individual embryo has a high implantation probability — roughly 60–70% for patients under 37. Transferring two PGT-A tested embryos creates a very high twin risk (40%+). For this reason, nearly all fertility societies recommend single embryo transfer when a euploid embryo is available, regardless of patient age.

💡 What Colombian Clinics Recommend

Colombian fertility clinics follow international guidelines and generally recommend SET for patients with good-quality blastocysts, especially when PGT-A has been performed. However, Colombian regulations do not restrict the number of embryos transferred — the decision is made collaboratively between you and your doctor based on your specific situation, age, embryo quality, and prior history.

The Cumulative Argument for SET

The strongest argument for SET is cumulative success. If you transfer one embryo at a time and it does not work, you transfer the next one. Two sequential single embryo transfers give you a cumulative pregnancy rate of 65–75% — comparable to one double transfer — with virtually zero twin risk. In Colombia, where frozen embryo transfers cost $1,500–$3,000, a second transfer is a modest investment compared to the costs and risks of a twin pregnancy.

Need Help Deciding?

Your Colombian fertility specialist will recommend SET or DET based on your age, embryo quality, and history. We can connect you with clinics for a personalised assessment.

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The Bottom Line

Transfer fewer, not more. Single embryo transfer is safer for both mother and baby, and cumulative success rates are comparable to double transfer when you account for the frozen embryo transfer that follows. The only "benefit" of DET is a modestly higher per-transfer pregnancy rate — and that comes with a 25–35% chance of a high-risk twin pregnancy. For most patients, SET is the responsible choice.