The chances of pregnancy with IVF are increased if more than one egg is recovered. To achieve this, the ovaries are stimulated with fertility drugs (super-ovulation) with the intention of growing at least three mature eggs. A number of different drugs and protocols are used in the treatment.

The most commonly used protocol for IVF involves first giving a drug called a gonadotropin releasing hormone agonist (GnRH agonist) either by daily injection or as a nasal spray. The aim of this drug is to temporarily suppress the woman’s natural hormones and control the timing of ovulation. This is called down-regulation and allows for greater control over the treatment cycle.

After ‘down regulation’ has been achieved (approx. two weeks), the GnRH agonist is continued, and injections of FSH ± LH are given to stimulate the ovaries.  The second protocol we use is called an Antagonist Protocol where an additional injection is introduced on day 5 or 6 of stimulation to again allow good control of the woman’s hormones.

Ultrasound Monitoring

Eggs are microscopic but they grow in fluid filled structures (follicles) which can be clearly seen on ultrasound scan. The development of the follicles is routinely monitored using vaginal ultrasound scans. After about 7-12 days of the injections, the follicles will almost be mature. The woman is asked to stop her stimulation drugs and a trigger injection called human chorionic gonadotropin (hCG) is given. The hCG injection is carefully timed and is usually given at night with the egg collection being performed 36 hours later in the morning.

Egg Collection

This is a minor surgical procedure, carried out at Merrion Fertility Clinic procedure rooms using ultrasound guidance. An Anaesthetist is present during the procedure providing excellent intravenous pain relief and sedation.

A vaginal ultrasound probe with a fine hollow needle attached to it is inserted into the vagina. Under ultrasound guidance, the needle is then advanced into the ovary to drain the fluid from each follicle. Each follicle is emptied in turn and the fluid is passed directly to the laboratory team, who search for the eggs. The eggs are identified and prepared for interaction with partner’s sperm. The whole procedure takes about 20-30 minutes.

Sample production

Before / during the egg collection procedure, the male partner will provide a semen sample that will be specially prepared and used to inseminate the eggs. Alternatively, if frozen sperm is to be used, this will be thawed out.

Insemination and Fertilization

Eggs are inseminated in the afternoon following the egg collection (‘day 0’) and are left overnight to fertilize. Usually about 60-70% of the eggs collected will be fertilized, but this can vary from 0% to 100%. Regrettably, some 3% of couples will not achieve fertilization of any eggs.

There are 2 ways to inseminate eggs.

Standard IVF: This is where a fixed concentration of motile sperm (100,000) are mixed with the eggs overnight. During the night the sperm should fertilize the eggs.

ICSI (Intra-Cytoplasmic Sperm Injection): This is used when there are not enough motile sperm to fertilize the eggs using the standard IVF method. Eggs are first checked to make sure they are mature as only mature eggs can be injected and subsequently fertilize. An individual sperm is then selected by an embryologist and injected directly into each egg.

Eggs are checked the following morning (‘day 1’) for fertilization and patients are phoned with the update.



Embryo and Blastocyst Culture

Following the fertilization stage, eggs progress on to the embryo stage. This is where the egg splits into 2 cells, then 3, 4 etc. Embryos are cultured or grown in the lab for a number of days. They are monitored regularly by the embryologists and the best embryo(s) are transferred back to the womb in a procedure called Embryo Transfer.

Embryo Transfers can happen on Day 2, Day 3 or Day 5.

The aim of embryo culture is to learn about the embryos and determine which are best and most likely to implant in the womb. If this choice is clear on Day 2 or Day 3 then the Embryo Transfer will be arranged. If it is felt that an extra 2 or 3 days would be helpful in making the decision, then culturing the embryos to Day 5 will be recommended. This is called Blastocyst culture, as by Day 5 embryos will have reached the next stage in their development – the blastocyst stage.

Embryo Transfer


The embryo transfer procedure is quite simple and is usually pain free. No anaesthetic is necessary. One or two embryos suspended in a drop of culture medium are loaded in a fine plastic catheter with a syringe on one end. Gently and carefully, the doctor or nurse guides the tip of the catheter through the vagina and cervix, and deposits the embryos into the uterine cavity. The procedure is guided using ultrasound scanning to check the position of the catheter.

Once the embryos have been replaced, the woman rests for a short while before going home. There is no chance of the embryos ‘falling out’ and women are advised to return to their normal routine as soon as possible.

The number of embryos to be replaced will depend upon several factors such as female age, previous pregnancies and number of cycles. It is well proven worldwide that the safest pregnancy, for both the mother and child, is a singleton pregnancy. Twin pregnancies are at an increased risk of miscarriage, premature delivery, foetal or neonatal death and cerebral palsy. This risk increases dramatically for triplets, quadruplets etc. Our policy is to transfer one or two embryos under normal circumstances. This will be discussed in detail with every couple prior to treatment and again on the day of embryo transfer.