Revealing this after announcing she was pregnant for the eighth time, it wasn't such a bad thing.

O'Callaghan attended a fertility clinic on Harley Street, London, which prescribed Clomid . . . a popular drug for treating the condition. "It certainly worked because I had three children in 11 months, " said the RTE presenter. "But I've always had to try hard to get pregnant. They say that fertility zooms down after 35 and some women are giving up, but I believe that if you keep healthy and eat well there is no reason why you can't go on."

Infertility can take a variety of different forms and treatment depends on the nature of the problem. According to Dr Edgar Mocanu, fertility expert at the Rotunda Hospital, Dublin, it's difficult to know whether there has been an increase in infertility in recent years or if it's simply that more people are seeking help for the condition.

"In general, a couple have an 80% chance of conceiving in their first year together, " he says. "They have a 90% chance in their second year so my advice to people is to keep trying and don't get downhearted if it doesn't happen immediately."

Dr Mocanu points out that factors such as smoking, inadequate diet, lack of sleep, abuse of alcohol and lack of exercise can all contribute to the problem. "Age too is a huge factor. The older a woman gets the more difficult it is for her to conceive, " he says. "In general, however, the better she looks after her body the easier it's going to be."

Infertility can be caused by a medical condition. The most common are non-ovulation, endometriosis or tubular disease. Each can be treated with a different drug but there are also herbal remedies which claim to help.

Anne Marie Keaveny, a professional medical herbalist, cautions against using herbs without the advice of a qualified herbalist.

"We generally advise women to use herbs for three months before they get pregnant, " she says. "This is because some of them should not be used while pregnant.

Also, some can be used in conjunction with orthodox medicine while others can not."

Members of the Irish Institute of Medical Herbalists are trained to assess potential drug herb interactions. A herbalist will tailor the herbal prescription, taking account of the diagnosis and the constitution of the patient in question.

Here are some treatments for a number of common causes of infertility:

Anovulation Clomid is a popular drug used to induce ovulation. Side effects include headaches, visual distress, hot flushes, moodiness and, in up to 10% of cases, multiple pregnancies.

Other medication includes a drug called Metforman which is not yet licensed but is becoming more popular.

Side effects include digestive problems and there is evidence to show it is hard on the liver. The drug Gonadotrophins is another treatment.