Earlier this week it emerged that 38-year-old royal Sophie Wessex has turned to IVF to try and have a child, but what does it actually involve? Women's Editor Christen Pears reports.

SINCE the first test tube baby, Louise Brown, was born in 1978, almost 70,000 babies have been born in Britain using the IVF method, and with one in seven couples unable to conceive naturally within a year, around 30,000 treatments are now carried out annually.

"We are able to identify the causes of infertility for some couples, which could be due to ovulation problems or male infertility, but there are also around 30 per cent of couples who have an unexplained infertility problem," says Dr Alison Murdoch, consultant gynaecologist at the International Centre for Life in Newcastle, the North-East's main centre for NHS treatment. "IVF is the first line treatment. It's not the end of the line as some people assume."

Although the procedure is relatively common, it's still a daunting prospect - and one with no guarantee of pregnancy. The Human Fertilisation and Embryology Authority (HFEA) publishes an annual guide to clinics, complete with success rates.

HFEA spokeswoman Vishnee Seenundun explains: "The decision to go for IVF comes from a couple in consultation with their GP. Their doctor will often then refer them to us and we will give them information about how they should go about seeking treatment and what questions they should ask the clinics.

"Clinic success rates vary but you should always find out if a clinic has seen someone of your age and fertility background. You must also feel comfortable and confident in the staff."

Some couples are put off by the cost, which can run into thousands of pounds. IVF is only available on the NHS in some areas of the country and around 80 per cent of treatment is carried out privately at a cost of between £1,500 and £3,000.

The Centre for Life treats between six and seven hundred couples a year, both on the NHS and privately. Last month, a new fertility centre opened in Darlington, which aims to treat up to a thousand families a year. The Cromwell IVF and Fertility Centre is based at the private Woodlands Hospital and will replace the Cromwell unit at the Washington BUPA Hospital on Wearside.

The clinic also operates a pioneering egg sharing scheme, in which couples can donate spare eggs in exchange for infertility treatment. It gives patients, who may not be able to afford private treatment, the chance to have their own baby.

But IVF puts significant physical demands on the patient, due to frequent visits to hospital, regular blood samples, ultrasound scans and surgical procedures.

It has an average success rate of 22 per cent and couples often require three or four treatment cycles before the woman conceives. Some never do. With such a high chance of disappointment, IVF can also take an emotional toll, and most clinics have counsellors on call to help couples with the psychological stress associated with treatment.

Dr Murdoch says: "Couples are referred by their GP, who will usually have carried out preliminary investigations before they come to us for their first visit.

"By their second visit, we can usually tell them what the cause is and they can decide if they want to go ahead with IVF. Not everyone wants to. If there is a chance of them getting pregnant on their own, they may want to keep trying."

An IVF cycle lasts seven weeks and begins with a five-week course of medication for the woman to make her grow more than one egg. The eggs are collected under sedation and are then put together with the sperm outside the woman's body in a culture dish. Any eggs that fertilise are left to grow for up to two days and then up to three embryos are implanted in the patient's womb in a delicate surgical procedure.

"At that stage, the embryo is tiny, the size of a pin head and just consists of four cells," says Dr Murdoch.

"We usually put two embryos in for the first treatment, as long as the couple are prepared for the possibility of twins. We then have to wait two weeks before we know if the implant has been successful."

If the remaining embryos are of a sufficiently high quality, they are frozen and can be used in another cycle if the first has been unsuccessful.

The programme at the Centre of Life has a 25 per cent success rate - three per cent above the national average. But while many women do conceive, there are others who are disappointed. TV presenter Anthea Turner spoke recently of her heartache after five failed attempts to have a test tube baby.

Dr Murdoch says: "IVF isn't a guarantee and couples have to be prepared for disappointment, but there are plenty who do go on to have the families they want."