In Vitro Fertilisation (IVF) literally means fertilisation in glass. Instead of sperm penetrating the egg within the body (in vivo), fertilisation takes place in a sterile disposable dish in a laboratory (In vitro).

Once the egg has been fertilised the resulting embryo is then transferred into the uterus with the hope of establishing a pregnancy. More than three million babies have been born using IVF and other assisted reproductive technologies (ART) since the worlds first IVF baby was born in July 1978.

Looking at the process in more detail, the first step is ovarian stimulation.The treatment at this stage relies upon fertility drugs to stimulate the development of follicles in the ovaries. Most of the fertility drugs used are given by subcutaneous injection and these injections carry on for approximately twelve days.

During the stimulation phase serial ultrasound scans are used to monitor the number and growth of ovarian follicles and the development of the lining of the uterus. The ovaries are stimulated to produce more eggs than in a normal cycle in order to improve the chances of achieving a pregnancy.

Egg collection is performed vaginally using a special needle guided by ultrasound. Each follicle is aspirated in turn until all the eggs are collected. The procedure is usually carried out under heavy sedation but sometimes a general anaesthetic is required.

After this the process moves to the laboratory where the sperm sample is assessed by an embryologist and a suitable method of preparation used to select the most active sperm for insemination. The eggs have their surrounding cells removed in preparation for the fertilisation process. The inseminated eggs are then placed in an incubator overnight and are checked the following morning to see how many have fertilised.

The fertilised eggs (embryos) are then cultured for between two and five days in the laboratory before being transferred into the uterus. The best one or two embryos are selected for transfer either two to three days after egg collection or cultured further until day 5 (Blastocyst transfer). Any other good quality embryos may be stored by freezing (cryopreservation) for possible transfer at a later date.

Sometimes, where the male partner has a low sperm count and/or poor motility or couples have experienced previous failure of fertilisation during IVF a procedure called Intracytoplasmic Sperm Injection (ICSI) is used. This involves the injection of a single live sperm directly into the centre of the egg using a very fine glass needle under a high power microscope. ICSI is a laboratory technique which helps fertilisation take place and is an extension of the IVF procedure.

In the UK all IVF clinics are regulated by the Human Fertilisation and Embryology Authority (HFEA). Figures produced by the HFEA reveal that approximately 24% of live births resulting from IVF and ICSI treatment are twins compared to less than 1% following natural conception.

Although the prospect of conceiving twins may be attractive to some couples having fertility treatment, the fact is that the risk of complications during a twin pregnancy is much higher with less chance of the babies being born healthy and developing normally.

Therefore, clinics are being encouraged to introduce an elective single embryo transfer (eSET) policy with the aim of reducing multiple pregnancy rates to levels recommended by the HFEA. Things to consider when implementing this policy include patient selection (younger patients with good quality embryos are best suited for eSET), selection of embryos for eSET and the day of embryo transfer.

There is evidence to show that it is now possible to transfer a single blastocyst on day 5 in patients who are keen to avoid a multiple pregnancy and still achieve success rates comparable to the transfer of two embryos on day 2-3. It will be interesting to see if this policy has any impact on overall success rates in the future.