New maths can predict the likelihood of getting pregnant

A new mathematical model has been devised to help couple’s calculate the likelihood of conceiving a child on the basis of age and how long they have been trying.

Researchers at the University of Warwick have been collaborating with those from the London School
of Economics (LSE). They also used the number of menstrual cycles over which the couple has been
trying for a baby to determine the probability of conception the following month.

The research determined that if the woman is aged 35, after just six months of trying, her chance of
getting pregnant in the next cycle is then less than 10 percent.

Professor Geraldine Hartshorne – who led the research and holds a joint appointment between Warwick
Medical School and University Hospitals Coventry and Warwickshire – said: “Many couples are
not aware that chance plays a big role in getting pregnant.

“People expect to get pregnant when they want to, so finding out that it isn’t happening can be a
shock. Approaching a doctor about such a personal matter is daunting so knowing when the right time to start investigations is would be a useful step forward.”

According to the model, when a woman is 25, it takes 13 menstrual cycles before her chance of pregnancy in each new cycle has declined to below 10 percent. The number of months required to
reach a conception chance below 10 percent cycle is 10 at age 30, and just six at age 35.

Dr Peter Sozou of the London School of Economics said: “After several cycles without pregnancy, it
becomes relatively more likely that a couple have low fertility. This is the main reason why it becomes less likely that conception will occur in the next cycle.

“We can’t work out exactly when, or if, a woman will become pregnant – but this analysis can predict
her chances, and give a percentage estimate of pregnancy in the next cycle.”

The mathematical model drew inspiration from 18th century minister Thomas Baynes who formulated a way to calculate probabilitiesby combining prior information with new evidence.

The paper entitled ‘Time to pregnancy: a computational method for using the duration of on-conception
for predicting conception’, is published in the open access journal PLOS ONE.