Researchers have developed a mathematical model for determining what age women should start trying to conceive.
If a woman wants a 90 percent likelihood of having one child without IVF, for example, the model suggests she should begin trying to conceive by the age of 32. Alternatively, if a woman wants a 90 percent likelihood of having three children without IVF, then it suggests she should begin trying at the age of 23.
'We have tried to fill a missing link in the decision-making process,' Professor Dik Habbema of Erasmus University in Rotterdam, the Netherlands, one of the model's creators, told New Scientist. 'My son is 35 and many of his friends have a problem deciding when to have children because there are so many things they want to do.'
The team took information on natural fertility from data collected on 58,000 women over the 300 years prior to the 1970s. They published details of the mathematical model in the journal Human Reproduction.
'You've got to factor in that people don't necessarily have children in quick succession,' Professor Allan Pacey, a fertility expert at Sheffield University who was not involved in the study, told New Scientist. 'What it is saying is that if you're relaxed about having three children, you can wait until you're 35, but you've got to start early to be certain.'
Pregnancy remains an option for women in their 40s, with the likelihood at 50 percent. Men's ages were not taken into consideration in developing this model because it does not influence fertility until they are in their late 40s.
Professor Ulla Waldenström, from the Karolinska Institute in Stockholm, told New Scientist, ‘In general, young people are very optimistic about their reproductive potential. They also have a lot of faith in reproduction technologies – there is a strong belief that if you can't get pregnant naturally, there is always IVF, although it is far from a guarantee.'
According to the model, IVF only increases the upper age for starting a family of any size by a few years. 'IVF has limited impact, and that might surprise people,' said Professor Habbema. He acknowledged that many other factors influence such decisions, including careers, relationships and childcare availability. 'It's not easy to make recommendations, but I hope the model will play a part in making decisions easier.'