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What is FER? Frozen embryo replacement, explained

Frozen embryo replacement (FER) is when embryos frozen during an earlier IVF cycle are thawed and transferred into the uterus to try for pregnancy. 

 What is FER? Frozen embryo replacement, explained

FER stands for frozen embryo replacement (also called a frozen embryo transfer). It's a procedure where embryos created and frozen during an earlier IVF cycle are thawed and transferred into the uterus, giving them the chance to implant and grow into a pregnancy.

How does FER work?

During a fresh IVF cycle, we can often create more than one embryo. We usually transfer the strongest embryo straight away, and freeze any remaining high-quality embryos so they're ready when you need them.

When you're ready for a FER cycle, here's what happens:

  1. We prepare your uterus. We use hormonal medication, such as oestrogen and progesterone, or monitor a natural cycle closely, so your womb is ready to receive the embryo.
  2. We thaw your embryo. This happens on the day of your planned transfer.
  3. We transfer the embryo. Using a thin catheter, we place the embryo into your uterus. It's a quick procedure, and most people find it no more uncomfortable than a cervical screening test.

Why choose FER?

Strong success rates. Frozen embryo transfers are now standard practice in clinics around the world, with pregnancy rates that are often comparable to, or slightly higher than, fresh transfers. This is because the hormones used in a fresh cycle can temporarily change the uterine environment, whereas a FER cycle gives us a calmer, more controlled setting for implantation.

Less time and cost. Because your eggs have already been collected and fertilised, a FER cycle means you won't need to go through egg retrieval again.

Genetic testing. If you choose pre-implantation genetic testing (PGT), your embryos need to be frozen. This gives us time to receive the biopsy results before we go ahead with the transfer.

Growing your family later. Frozen embryos can be stored for years, so they're often the right choice when you're ready to try for a sibling further down the line.

Frequently asked questions

What does FER stand for? FER stands for frozen embryo replacement.

Is FER more successful than a fresh embryo transfer? Success rates vary between individuals, but frozen embryo transfers often achieve pregnancy rates that are comparable to, or slightly higher than, fresh transfers.

Does a frozen embryo transfer hurt? No. It's a quick procedure that most people compare to a cervical screening test.

Do I need to go through egg retrieval again for FER? No. Because your eggs have already been collected and fertilised, FER skips this step entirely.