Calculating when it is the right time to conceive


A mathematical model shows that women in their mid-30s shouldn’t wait to seek help in having a baby

Women are under pressure to deliver a lot in life; a good education, forge a career, find a partner and, perhaps the most demanding of all, to buy a house. However, women in their mid-30s are now being advised not to wait to seek medical help if they are unsuccessful in conceiving a child after six months of trying.

A woman aged 35 has less than a 10 per cent chance of conceiving during her next menstrual cycle following a period of six months of unsuccessful attempts, according to researchers at the University of Warwick and the London School of Economics.

This 10 per cent chance that a woman will conceive also falls dramatically as she ages over the following years, leaving a woman of 40 with almost no chance of conceiving naturally if she does not become pregnant within the initial six months of trying.

“You can make the argument that for a woman aged 35, this research would show that it would be beneficial to seek medical help after six months [of trying] and not wait any longer,” said Dr Peter Sozou of the London School of Economics, who used a mathematical method, known as Bayes’ theorem, to predict the probability of conception.

By calculating the number of menstrual cycles over which a couple has been trying unsuccessfully for a baby, the researchers were able to determine the probability of conception within the next month.

When a woman is 25, it takes 13 menstrual periods before her chance of pregnancy in each new cycle has declined to below 10 per cent, according to the model.

The number of months required to reach a conception chance below 10 per cent cycle is 10 at age 30, and just six at age 35.

“Women are now achieving a lot in life and planning a family can be pushed to the side,” explained Prof Geraldine Hartshorne of the University of Warwick.

“It’s not necessarily in keeping with our society but we should get the message out to women that this is something they should be aware of and educated in, and, if they decide that they do want to have children, that they don’t leave it too late.”

The results move away from the rule of the thumb that couples should try to conceive naturally for a year before approaching their GP.

However, it does conform with advice from the Irish Fertility Society that women who are aged 38 should seek medical consultation earlier.

Yet it appears that Irish women are waiting much later than their European counterparts in seeking fertility treatment.

Women of 38 are the most common in bringing their concerns to a GP, yet in Scandinavia, doctors tend to see women in their early 30s.

The cost of private fertility treatment is indeed a factor in delaying treatment, reports Dr Mary Wingfield, medical director of the Merrion Fertility Clinic and a consultant obstetrician and gynaecologist at the National Maternity Hospital, Holles St, who has seen a rising number of patients being referred for consultation in recent years.

However, while couples were happy to undergo four or even five rounds of IVF treatment during the boom years she now sees more and more who are very stressed about the costs of treatment, which can reach € 4,000 or even € 5,000.

“Less couples are taking fertility treatment while an increasing number are unable to afford more than one cycle, or any at all.”

She recommends couples start to plan their family in their early 30s as for those who begin when the woman is 38 or 39, not only is there a higher chance that they will face problems with trying to get pregnant, but these couples also face a higher chance of miscarriage.

Aged 40, a woman has a one in three chance of miscarriage and this rises to a 50/50 chance as the woman turns 41 or 42. The researchers’ findings could form evidence for a new ‘golden rule’, that women in their mid-thirties should approach their GP straight away after six months of unsuccessful conception.

Of course, seeking medical advice can put pressure on a couple and their relationship and Dr Wingfield advises that while it is “probably helpful to approach a GP, it is not necessary to see everyone”.

Luck also plays a big part in conception and so if the couple have not suffered from any previous conditions such as chlamydia, a GP will likely encourage waiting a year before seeking treatment.