IVF and Twins — Why Single Embryo Transfer Is Safer

“Can we put two embryos in to double our chances?” It’s the most common patient request in IVF — and the most important one for your clinic to gently decline. Here’s why transferring two doesn’t double your baby rate but does multiply your risk, and why single embryo transfer (SET) is now the recommended standard worldwide.

The Maths That Misleads

If one embryo has a 40% chance of implanting, two should give 80%, right? No. The real calculation: two embryos each at 40% gives a 64% chance that at least one implants — and a 16% chance that both do. You haven’t doubled your chance of a baby; you’ve added a 1-in-6 chance of twins. And twin pregnancy is not double the joy — it’s a fundamentally different medical event.

Why Twin Pregnancy Is Genuinely Risky

For the babies: twins are 5–7 times more likely to be born premature (before 37 weeks), with all the consequences that carries — NICU stays, breathing difficulties, feeding problems, and long-term developmental risks. Very preterm birth (before 32 weeks) is uncommon in singletons but significantly more common in twins. Low birth weight affects over half of twins.

For the mother: twin pregnancy doubles the risk of pre-eclampsia, gestational diabetes, anaemia, postpartum haemorrhage, and caesarean delivery. The physical burden of carrying twins is substantially greater — and for a woman who has already been through IVF stimulation, retrieval, and the emotional weight of treatment, it’s a complication she didn’t sign up for.

Financially: a NICU stay for premature twins can cost more than the entire IVF cycle. The “savings” of transferring two to avoid a second transfer vanish instantly if both implant.

Why SET Works Just as Well — Over Two Transfers

The correct comparison isn’t “one transfer of two embryos vs one transfer of one” — it’s “one transfer of two vs two sequential transfers of one each.” Studies consistently show: cumulative live birth rates are equivalent. SET across two cycles gives you the same chance of taking home a baby as double transfer in one cycle — without the twin risk. The second transfer uses a frozen embryo at ₹40,000–70,000, a fraction of a fresh cycle.

The only scenario where double transfer has a genuine (modest) cumulative advantage is in women over 40 with very few embryos and very low per-embryo odds — and even there, the twin risks must be weighed against the marginal probability gain.

Why Some Clinics Still Transfer Two

Incentives. A clinic’s success rate is reported per transfer. Transferring two embryos inflates the per-transfer pregnancy rate (more implantations) at the cost of your health. A clinic that routinely transfers two and reports a 55% pregnancy rate may actually be delivering worse outcomes (more NICU, more complications) than a clinic transferring one and reporting 40%. Ask your clinic: “What is your twin rate?” — if it’s above 10–15%, they’re transferring too aggressively.

When Double Transfer Might Be Discussed

Some specialists offer it for women over 40 with untested embryos and very limited supply, or after multiple failed SET transfers. Even in these cases, it’s a discussion — not a default — and the risks should be explicitly consented. If your clinic proposes double transfer without discussing twin risks in detail, that’s a red flag about whose statistics they’re optimising.

The Bottom Line

One embryo, one transfer, one healthy baby. If it doesn’t work, your frozen embryo waits for the next cycle. The path to the same outcome is slightly longer but dramatically safer. Our clinic selection guide includes SET policy as one of the seven questions that reveal clinical quality.