What happens in the majority of cases is summarized below:

1. The woman’s ovaries are stimulated for a few days with hormones (ovarian stimulation).
2. When the eggs mature, they are harvested with a procedure called egg collection
3. On the day of egg collection, the man produces semen that the embryologists process in the lab
4. The eggs that have been collected are then fertilized by the sperm either by classical in vitro fertilization (IVF) or by intracytoplasmic sperm injection (ICSI)
5. When eggs are fertilized by sperm, embryos are produced
6. The embryos are left to grow for a few days in specialized ‘ovens’ called incubators
7. On the right day (2-5 days after egg collection), 1-4 embryos are placed inside the womb with a procedure similar to the smear test (this is called embryo transfer).
8. If there are good quality embryos left after embryo transfer, they can be cryopreserved (i.e. frozen) and used – if needed – in the future

(In some protocols, PRIOR to ovarian stimulation with hormones, there is a stage when suppression of the normally produced hormones is performed).

Now, in much more detail:

Normally one single egg matures in each monthly cycle.

The goal of conventional IVF is to stimulate the ovaries to produce as many mature eggs as it is safely possible (there also cases where natural IVF/mild IVF is pursued – i.e. the goal is to produce only 1-2 mature eggs).

OVARIAN STIMULATION

This is achieved by using injectable hormonal drugs that stimulate the ovaries to produce more mature eggs than usual.

During ovarian stimulation – in some protocols – other injectable medications may also be given that prevent ovulation from happening before the desired day.

To put it simply, it’s almost like driving a car and stepping mainly on the accelerator (ovarian stimulation medications), but also a bit on the brake (medications to avoid premature ovulation) as well.

The drug treatment (the so-called ‘protocol’) must be individualised – that is, it should be tailored to each woman’s needs according to her characteristics (age, history, test results, etc.) This is why the dose of medications is not the same for every woman. And in this case, ‘the more, the better’ does not apply, because high doses of medications can cause ovarian hyperstimulation syndrome (OHSS), which should be avoided.

On top of that, the woman should be monitored with vaginal ultrasound and blood tests every 2-3 days (for a total of 10-12 days).

It is crucial for the fertility expert to know how the ovaries respond to the hormonal therapy, so he/she can change the dosage regime (if necessary), because ovarian response to medications may vary from woman to woman.

When the eggs are large enough, final maturation is induced by a different hormonal injection.

EGG COLLECTION AND FERTILIZATION

The egg collection is performed about 32-36 hours after the last injection that matures the eggs.

It is a simple procedure done through the vagina and lasting 10-30 minutes.

The fertility expert uses a small needle that draws fluid containing the eggs from the ovary under ultrasound guidance, while the woman is under light sedation.

In the meantime, the sperm (provided by the partner or a donor) is being washed and concentrated in preparation for its use.

The eggs are then taken to the lab, where they are fertilized by the processed sperm by using either the IVF or ICSI technique.

During conventional IVF, a number of sperm (approximately 100,000) are mixed together with the eggs into a special ‘dish’, where fertilization occurs in a natural manner (without any additional intervention by the embryologist). Only one sperm penetrates the outer layer of each egg to achieve fertilization.

In the case of ICSI, the embryologist selects a single healthy sperm and injects it directly into the egg with the help of a powerful microscope.

It should be emphasized here that not all collected eggs will necessarily be fertilized.

The fertilization percentage depends on the ability of the sperm to penetrate the egg (in conventional IVF), but also on the ability of the egg to ‘fuse’ with the sperm successfully (both in conventional IVF and in ICSI). On average, out of every 10 eggs that are collected, 7 or 8 will get fertilized.

Following fertilization, the cells divide and multiply to form an embryo. Embryos continue to develop and they are cultured in total for 2-5 days into special incubators in conditions resembling those inside the body.

Again, not all embryos left for culture will necessarily continue to grow normally. Some will stop growing and will not be used.

Unfortunately, ‘wastage’ is part of every IVF cycle and this is exactly why the aim is to collect as many eggs as possible to start with.

EMBRYO TRANSFER

Out of the normally developing embryos, 1-4 are selected (depending on their number and quality, but also on the age and preferences of each woman) for transfer into the womb.

Embryo transfer occurs on the 2nd to 5th day after the egg collection (depending on the available embryos).

This is a quick and painless procedure that does not require anaesthesia.

The woman prepares as for a smear test, but she needs to have a full bladder to facilitate the embryo transfer.

The fertility expert places the same instrument used for the smear test (speculum) in the vagina and cleans the neck of the womb (‘cervix’). The embryos are then loaded into a small syringe which is attached to a thin and flexible plastic tube (‘catheter’). The catheter passes through the cervix and when it reaches the cavity of the womb, the plunger of the syringe is advanced slowly and the embryos are deposited inside the womb.

The embryos will then hopefully implant and form a pregnancy.

The whole procedure is usually performed under ultrasound guidance to precisely confirm the location of the deposited embryos.

The woman then takes some medications and, after 10-12 days, a blood test is performed to determine if there is a pregnancy.

Ultrasound scans are then arranged as per any pregnancy.

An informative video on how IVF is done can be found here (from 0:45 to 2:35)