IVF and Single Embryo Transfer (SET): One Embryo at a Time

• Single embryo transfer (SET) means putting back one embryo per cycle and freezing the rest for later — it does not throw away your chances, it spreads them out safely.
• Transferring two embryos roughly doubles the twin rate, and twin pregnancies carry much higher risks of preterm birth, NICU admission, preeclampsia and other complications.
• Over a full course of treatment (one fresh transfer plus frozen transfers), SET gives similar cumulative chances of a baby as transferring two — but with far fewer twins.
• SET is strongest for women under 35 with a good blastocyst, and for any age with a PGT-A-tested (chromosomally normal) embryo.
• Modern embryo freezing (vitrification) gives over 95% survival, so frozen transfers work just as well as fresh — this is what makes one-at-a-time possible.
• The decision is yours: ask your clinic about its twin rate, cumulative success and total cost before stimulation begins.

Single embryo transfer (SET) is the IVF practice of transferring exactly one embryo per cycle, with any other good-quality embryos frozen for a future frozen embryo transfer (FET) if needed. Elective SET (eSET) means choosing to transfer one embryo when two or more good ones are available — different from simply having only one embryo to transfer.

The opposite is double embryo transfer (DET), where two embryos are put back together. Until the early 2000s, DET was the global default, because IVF success rates per transfer were low and clinics wanted to maximise the chance of any pregnancy.

Three things changed that. Embryos can now be grown to day-5 blastocyst stage rather than day-3, so the strongest embryos select themselves. Selection tools improved, including genetic testing of embryos and time-lapse imaging. And the harms of twin pregnancy became impossible to ignore.

Countries like Sweden, Belgium, Australia, the UK, Japan, Norway and Finland now have national policies favouring eSET. In Sweden, more than 90% of IVF transfers use a single embryo, and IVF twin rates are under 5%. India is moving in the same direction, more slowly. ISAR (the Indian Society for Assisted Reproduction) consensus statements from 2018 onward recommend eSET as best practice, with FOGSI backing. The 2021 ART Act brought regulation to Indian IVF but did not set an embryo-transfer policy. Most major Indian clinics now offer eSET for younger patients with good blastocysts, while DET remains common for older patients, repeat IVF failures and poorer-quality cycles.

Twin and higher-order pregnancies are the central problem SET is designed to prevent. Many Indian couples see twins as a welcome bonus — do bachche ek hi baar mein, a way to complete the family in one go and avoid another expensive cycle. The medical reality is more sobering: a twin pregnancy carries substantially higher risks for both mother and babies than a single pregnancy.

For the mother, a twin pregnancy raises the risk of preeclampsia (high blood pressure) by around 3–5 times, roughly doubles the risk of gestational diabetes, and makes severe vomiting, preterm labour, caesarean delivery (over 70% of twins) and postpartum haemorrhage more likely.

For the babies, the biggest danger is prematurity. Over half of twins are born before 37 weeks, compared with about 10% of single babies. That means more low birth weight, more NICU admissions (50–60% of twins), and higher rates of breathing problems, brain bleeds, and longer-term complications including cerebral palsy and developmental delay.

Higher-order multiples (triplets or more) are riskier still, with over 90% born preterm and almost universal NICU care. International bodies — ASRM, ESHRE, ACOG, NICE — and India's FOGSI and ISAR all regard avoidable multiple pregnancy from IVF as a preventable adverse outcome. In well-run IVF systems, twin rates have fallen from over 25% to under 5% with eSET, while overall live-birth rates held steady. In India, IVF twin rates remain around 20–30% because DET is still common; ISAR's goal is to bring this below 10%.

• Strongest fit: under 35, good blastocyst, first or second cycle, or any age with a PGT-A-normal embryo.
• Also reasonable: age 35–40 with a good blastocyst, or a previous IVF baby.
• Discuss carefully: over 40 without PGT-A, repeated implantation failures, or only day-3 embryos available.
• Strong medical reason for SET: heart disease, severe diabetes, or prior severe preeclampsia where a twin pregnancy would be hazardous.

On a single transfer, DET does look better. Per-transfer live-birth rates are typically around 40–50% for DET versus 30–40% for eSET in good-prognosis patients — because two embryos give two chances at once. This gap is exactly why many couples and some clinicians still lean toward DET.

But that comparison is misleading, because it ignores cumulative success. Cumulative live-birth rate counts the total babies from one egg-collection cycle, including every fresh and frozen transfer of those embryos. Measured this way, eSET plus subsequent frozen transfers gives cumulative success similar to a single DET cycle (roughly 50–70% for good-prognosis patients) — without the twin rate.

The landmark trial here is Thurin and colleagues (2004, New England Journal of Medicine), in which cumulative live-birth rates were 38.8% for eSET-plus-frozen versus 42.9% for DET — not significantly different — while multiple pregnancy fell from 33.1% to 0.8%. Later work, including a Cochrane review, confirmed equivalent cumulative success with a dramatic drop in multiples.

For Indian couples, the practical message is this: choosing eSET does not meaningfully reduce your overall chance of taking home a baby — it just spreads the attempts out. The real trade-offs are time (eSET may need one or two extra frozen-transfer cycles, adding 2–6 months) and upfront cost, which we cover below.

The shift to SET is only possible because we can now pick the best embryo more reliably.

Day-5 blastocyst culture replaced day-3 transfer. Only the most developmentally capable embryos reach blastocyst stage (typically 30–60% of fertilised eggs), so reaching this milestone is itself a natural selection step.

Morphological grading uses the Gardner scale: a number (1–6) for how expanded the blastocyst is, then two letters (A–C) for the inner cell mass (future baby) and trophectoderm (future placenta). Top-grade blastocysts (such as 3AA, 4AA, 4AB) have the highest implantation rates and are the natural choice for eSET.

Time-lapse imaging (systems such as EmbryoScope) lets the lab watch embryos develop without removing them from the incubator, refining selection. It is offered at several premier Indian clinics for an additional Rs 25,000–60,000 per cycle.

PGT-A (preimplantation genetic testing for aneuploidy) takes a tiny biopsy from each blastocyst and checks the chromosome count. A euploid (chromosomally normal) embryo has the highest chance of becoming a healthy baby, which is why PGT-A supports eSET even in older women. In India it typically costs Rs 25,000–40,000 per embryo tested and is most useful after age 35, or with recurrent miscarriage or implantation failure. Some clinics also offer PGT-M and PGT-SR for specific inherited conditions — relevant if you and your partner are carriers, as carrier screening may reveal.

SET depends on reliable freezing, because the whole point is transferring one embryo at a time across several cycles.

Modern vitrification — ultra-rapid freezing — gives blastocyst survival rates above 95%. Frozen transfers produce live-birth rates equal to, and sometimes slightly better than, fresh transfers (supported by Cochrane and ESHRE data), so freezing does not waste good embryos.

Freeze-all means no fresh transfer at all — every embryo is frozen and transferred in a later cycle. Clinics choose this when there is a high risk of ovarian hyperstimulation syndrome (OHSS), when hormone levels at trigger suggest the fresh lining will not be receptive, when the lining is thin, or when PGT-A is planned (the biopsy needs time for analysis).

In India, vitrification with first-year storage typically costs Rs 25,000–60,000, then Rs 10,000–20,000 per year. The ART Act sets storage limits, with extensions on request. A frozen-transfer (FET) cycle costs around Rs 50,000–90,000 and uses either a natural-cycle protocol or a hormone-replacement protocol (oestrogen, then progesterone such as Susten or Duphaston) to prepare the lining. Combined with eSET, this lets you draw one embryo at a time from a single egg collection — balancing per-cycle safety with cumulative success.

Cost is the single biggest reason DET persists in India despite the evidence. A fresh IVF cycle costs roughly Rs 1.2–2.5 lakh, with ICSI, FET, PGT-A and add-ons (time-lapse, embryo glue, receptivity testing) each adding tens of thousands more.

Almost all of this is paid out of pocket. Most private health policies exclude IVF; only a handful of corporate group plans include limited cover, and government schemes such as Ayushman Bharat do not currently fund IVF. IRDAI's 2023 guidance nudged insurers toward infertility cover, but uptake is slow. Faced with these bills, many couples request DET, hoping to succeed in one go.

This is understandable but often financially short-sighted. The costs of premature twins — NICU stays running into lakhs over several weeks, plus maternal complications and long-term follow-up for preterm babies — can far exceed the cost of one or two extra frozen-transfer cycles. ISAR economic modelling has estimated that IVF twins cost 2–4 times more than IVF singletons even before counting NICU. If you are weighing DET for cost reasons, ask your specialist for a cumulative cost projection that includes the realistic cost of a twin pregnancy, not just the headline price per transfer.

• What is your default embryo-transfer policy for my age and prognosis?
• What is your clinic's IVF twin rate, and your blastocyst rate per fertilised egg?
• Do you offer time-lapse imaging and PGT-A, and at what cost?
• How many embryos do you recommend for me specifically, and why?
• What is the cumulative live-birth rate for eSET-plus-FET versus DET in your data?
• What is the total cost of eSET with possible frozen transfers versus DET?

Family and cultural dynamics deserve honest discussion. In many Indian families the wish for twins is openly expressed — do bachche ek hi baar mein, finishing the family in one pregnancy, avoiding the cost and effort of a second cycle. Elders and in-laws may actively push couples toward transferring two embryos.

These feelings are real and understandable, but they should not override the medical evidence. India already has one of the world's highest preterm-birth rates, and twins amplify that risk sharply. NICU capacity is limited and expensive outside major metros, so extreme prematurity from twins can mean transfer to a distant hospital, weeks of family separation, and serious financial strain. The early enthusiasm for twins often fades once families live through NICU stays, round-the-clock feeding and the demands of two newborns at once.

Many ISAR-affiliated clinics now build family counselling and twin-risk education into pre-IVF consultations, and some offer sessions for relatives to take pressure off the couple. ISAR's position is clear: the decision belongs to the couple and their doctor, with family input welcomed but not determinative. If pressure for DET is overriding your medical advice, ask your IVF doctor to explain the risks directly to your family — most are happy to. Preparing emotionally for the ups and downs of this journey, and talking it through openly with your partner, can make these conversations easier.

• You have a medical condition — heart disease, severe diabetes, previous severe preeclampsia, or a uterine anomaly — that would make a twin pregnancy hazardous.
• You are under 35 with a good blastocyst but are being offered DET as the default.
• You have a history of recurrent miscarriage or recurrent implantation failure and want to understand whether PGT-A could help.
• You and your partner are carriers of an inherited condition picked up on carrier screening.
• You feel pressured toward DET for non-medical reasons and want an objective discussion of the risks.
• If you do conceive twins, you will need closer antenatal monitoring — report any early warning signs of preeclampsia or preterm labour promptly.

• ASRM — Guidance on the limits to the number of embryos to transfer (committee opinion)
• ESHRE — Guideline on the number of embryos to transfer
• Thurin A, et al. Elective single-embryo transfer versus double-embryo transfer in in vitro fertilization. N Engl J Med, 2004
• Cochrane — Number of embryos for transfer following in vitro fertilisation or intra-cytoplasmic sperm injection
• NICE — Fertility problems: assessment and treatment (CG156)
• Indian Society for Assisted Reproduction (ISAR)
• Government of India — The Assisted Reproductive Technology (Regulation) Act, 2021