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. Side effects include upset stomach.

Non-regular menstrual cycle If a woman has a regular menstrual cycle and there appears to be no specific medical reason for failure to become pregnant, herbal remedies may be of use.

Valerian, camomile and oats all have relaxing effects on the body and can help with the stress of trying to get pregnant. Liver herbs such as milk thistle and dandelion root both help to regulate functioning of the liver and gall bladder where enzymes are broken down.

Vites can help to regulate the menstrual cycle where there are menstrual irregular periods.

Endometriosis Endometriosis is a condition whereby the lining of the womb grows outside the uterus. If the condition is mild, it can be treated with laser therapy or endocoagulation.

If it's more severe, affecting the bowel or vagina, it could require surgery.

"Research is ongoing, " says Dr Mocanu. "We still don't understand why it happens and for that reason it can be difficult to treat. It is, however, a progressive disease and is best caught in the early stages."

Herbs which may help include black cohosh, which has an oestrogenic effect on the body. Wild yam is another herb with oestrogenic properties, which helps the body's response to the condition.

Both have anti-inflammatory properties and therefore may reduce the body's inflammatory response. Together with other herbs, the approach is to reduce pain, regulate the menstrual flow and reduce inflammation.

Tubular disease If a woman has blocked tubes, her age is important when treating it. If she is still in her 20s or early 30s she can be treated with tubular micro surgery. This is a serious operation. It has, however, been used for years and has become more refined with time. As such, it has a high success rate.

Hydrocotyl is a herbal remedy used to reduce adhesion.

Vitamin E can also help in reducing adhesions. It may help if the case is mild but its effectiveness is unproven in severe situations.

Polycystic Ovarian Syndrome The herbal approach in this condition involves assisting blood sugar balance in conjunction with normalising ovulation and reducing androgen levels.

Bitter herbs such as gentian and fenugreek are known to help the digestive process and balance blood sugar levels. Anti-inflammatory herbs such as wild yam and marigold are useful as they reduce inflammation. Herbalists would also use many other strategies specific to the patient in question.