In brief: Almost every couple approaching transfer day asks the same thing: “Should we transfer one embryo or two?” Many assume two embryos double the odds. They don’t. This article answers one question: how many embryos should be transferred in IVF, and what should that decision be based on?

Two embryos do not double your chances

An embryo’s chance of implanting does not go up because a second embryo is placed next to it. Transferring two embryos raises the pregnancy rate for that transfer somewhat, but the twin rate climbs much faster. In younger women receiving two good-quality blastocysts (day-5 embryos), the twin rate can approach one in three.

The key point is this: when good embryos are transferred one at a time (the first fresh or frozen, and if no pregnancy follows, the second in the next cycle), the cumulative live birth rate comes very close to transferring both at once. The difference is not large enough to justify the risks of a twin pregnancy. How we make this decision, and every step of treatment at our clinic, is described on our page about IVF treatment in Istanbul.

Why twins are not “two for the price of one”

Some of my patients openly hope for twins: “two children in one go, no more treatment.” It is an understandable wish. But a twin pregnancy carries clearly higher risks than a singleton:

• More than half of twins are born before 37 weeks; preterm birth is the main reason babies need neonatal intensive care.
• Low birth weight is far more common in twins.
• For the mother, the likelihood of preeclampsia, gestational diabetes, bleeding and cesarean delivery increases.
• The risk of miscarriage and pregnancy loss is higher than in a singleton pregnancy.

This is why fertility societies worldwide and Turkish regulations point in the same direction: the goal is one healthy baby.

What do the rules say in Turkey?

In Turkey, the number of embryos transferred is not left to the physician’s or the couple’s preference. It is limited by Ministry of Health regulation:

• Under 35: a single embryo in the first two attempts; from the third attempt onward, a maximum of two.
• 35 and over: a maximum of two embryos from the first attempt.
• More than two embryos are never transferred, in any situation.

I explained the reasoning behind these rules, and the full framework of IVF regulation in Turkey, in the article Is IVF in Turkey safe? In short: the limit exists not to reduce your chances, but to prevent the avoidable harm of multiple pregnancy.

What is the decision based on?

1. The woman’s age

With age, the proportion of chromosomally normal embryos falls. Under 35, a good-quality blastocyst has a high chance of implanting; one embryo is enough. Over 38, because a single embryo is less likely to be normal, the rules allow two. But that does not mean two are always transferred.

2. The embryo’s stage and grade

A day-5 embryo (blastocyst) has proven itself more than a day-3 embryo; its implantation potential is higher. If a good-quality blastocyst is available, a single transfer may be more sensible than two average-quality day-3 embryos.

3. Has genetic testing been done?

If the embryo has had genetic testing (PGT) and its chromosomes are normal, single embryo transfer is recommended regardless of age. A normal embryo already has a high chance of implanting, so adding a second brings twin risk rather than benefit. I covered who this testing is useful for in the article on PGT/NGS in IVF.

4. Previous attempts

If good-quality embryos have failed to implant several times, transferring two becomes a real option. Before that, though, correctable causes need to be reviewed: the uterine cavity, fluid in the tubes, clotting and thyroid problems. Adding an embryo does not fix an underlying problem.

5. The mother’s health and uterus

Previous uterine surgery, a uterine septum, high blood pressure or diabetes make a twin pregnancy harder on the mother. For these patients, single embryo transfer is not just advice; it is a safety requirement.

Are frozen embryos wasted, then?

No. The single embryo transfer approach relies on freezing good embryos and using them in sequence. With today’s freezing technique (vitrification), embryo survival after thawing is very high, and pregnancy rates from frozen transfers are no lower than fresh ones. So if the first transfer does not work, you can use the second embryo the following month without another egg retrieval.

What do the numbers say?

At our center, across all age groups, the pregnancy rate per transfer is 63% and the ongoing pregnancy rate is 47%. These results were achieved mostly with single embryo transfers. They are averages; your personal chance depends on your age, embryo quality and history. No number of embryos guarantees a pregnancy.

How we decide on transfer day

• We review your age, ovarian reserve and previous attempts.
• Together with the embryologist, we look at the day and grade of each embryo.
• If genetic testing was done, we consider the result.
• Within Turkish regulations, we tell you plainly which options are open to you and the twin risk of each.
• We decide together, and the number of embryos is chosen with a reason, not by instinct.

Appointments and contact

How many embryos to transfer is a separate question for every couple. To discuss your situation, your embryos and the plan that suits you best, you can book an appointment at our clinic at Biruni University Hospital in Istanbul. If you are traveling from abroad, we plan the schedule together from the start.

This article is for information only and does not replace a personal examination and medical assessment. Regulations may change over time; treatment decisions should be made together with your physician.