How Many Embryos Should You Transfer?

It’s one of the biggest decisions in an IVF cycle: how many embryos should go back into the uterus? More embryos might seem like a better chance - but that’s not always true, and in some cases, it can increase risks for both parent and baby.

UK Rules on Embryo Transfer Numbers

In the UK, the HFEA (Human Fertilisation and Embryology Authority) sets clear guidelines to reduce multiple pregnancy risk:

• Under 40: Usually a single embryo transfer (SET) if good quality embryos are available.

• 40–42: Up to two embryos may be transferred if appropriate.

• Over 42: May be offered two embryos, but outcomes are often lower.

Clinics are encouraged to transfer only one embryo at a time in most cases, especially if the embryos are high quality.

Single Embryo Transfer (SET): Pros & Cons

Pros:

• Reduces the risk of twins or higher-order multiples.

• Safer pregnancy - lower rates of preterm birth, low birth weight, and complications like pre-eclampsia.

• Allows another embryo to be frozen for future use.

Cons:

• May feel like a “lower chance” in that single cycle (although research shows SET with high-quality embryos has very good success rates).

Double Embryo Transfer (DET): Pros & Cons

Pros:

• Can slightly increase per-cycle pregnancy rates, especially in older patients or those with lower embryo quality.

• May be considered if you’ve had several unsuccessful SETs.

Cons:

• Higher risk of multiple pregnancy (twins or more).

• Greater strain on the body during pregnancy.

• Increased risk of NICU stays for babies, even if they’re healthy.

What the Data Says

HFEA statistics show:

• In women under 35, single blastocyst transfers have pregnancy rates close to double transfers — without the increased risk of twins.

• Twin pregnancies carry a higher chance of premature birth, low birth weight, and delivery complications.

Factors That Influence the Decision

Your clinic will consider:

• Age

• Embryo quality (fresh vs frozen, day 3 vs day 5)

• Previous IVF history

• Overall health and pregnancy risk factors

• Number of embryos available

Bottom Line

Transferring more embryos doesn’t always mean a better outcome — it can mean more risk. In the UK, single embryo transfer is the norm for good-quality embryos, with double transfers used selectively. The goal is one healthy baby at a time.