Behind the scenes of an IVF laboratory

When you go through IVF, you see your nurse and doctor, you have the procedures, and you feel every injection. What you don't see is the laboratory, where your eggs and sperm become embryos. Here is a general walk-through of what typically happens. Details vary between clinics.

Egg collection

Eggs are collected from the ovaries in a short procedure, usually under sedation. The fluid from each follicle is passed to an embryologist, who searches it under a microscope, identifies each egg, and counts them. Eggs are kept warm, at body temperature, and in controlled conditions from the start.

Keeping track of identity

Many clinics use electronic witnessing: barcodes or chips on every dish and tube, checked at each step, so that eggs, sperm, and embryos are always matched to the right patient. If something doesn't match, the system raises an alarm. Other clinics use careful manual double-checking by two staff members.

Preparing the sperm

The sperm sample is processed to separate the most active sperm from the rest of the semen, often using a density gradient and a centrifuge, followed by washing.

Fertilization: IVF or ICSI

In conventional IVF, eggs and prepared sperm are placed together in a dish so fertilization can happen on its own. In intracytoplasmic sperm injection (ICSI), an embryologist injects a single sperm directly into each egg. The HFEA describes ICSI as the most common treatment for male infertility.

Some clinics also offer high-magnification sperm selection (IMSI). The HFEA rates it grey, meaning there is not enough good-quality evidence to say whether it improves the chance of having a baby.

Embryo culture and monitoring

Fertilized eggs are placed in incubators that control temperature and gases. Embryos are checked for signs of fertilization the next day and then grow for up to 5 or 6 days, reaching the blastocyst stage. Some clinics use time-lapse incubators that photograph embryos every few minutes, and some use software or AI to help rank embryos. A Cochrane review found insufficient good-quality evidence that time-lapse systems improve live birth rates, and the HFEA rates time-lapse with automated embryo analysis as having no effect on the chance of having a baby for most patients.

Genetic testing

If a couple is at risk of passing on a specific genetic condition, a few cells can be taken from the outer layer of a blastocyst for testing, and the embryos are frozen while results are awaited. Testing embryos for chromosome number (PGT-A) is also offered, but the HFEA rates it red for improving the chance of having a baby for most patients.

Transfer and freezing

Usually one embryo is transferred to the uterus. Other good-quality embryos can be frozen using vitrification, a fast-freezing method, and used later if the first transfer doesn't work or for a future sibling.

Questions to ask about the lab

• How do you track eggs, sperm, and embryos to prevent mix-ups?
• Do you use IVF or ICSI for patients like me, and why?
• Which lab techniques are included, and which are extra-cost add-ons?