Want one鈥� or three? (Image: Christoph Eberle/Plainpicture)
IT鈥橲 a question many people will ask themselves at some point in their lives: when should I start a family? If you know how many children you鈥檇 like, and whether or not you would consider, or could afford, IVF, a computer model can suggest when to start trying for your first child.
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Happy with just one? The model recommends you get started by age 32 to have a 90 per cent chance of realising your dream without IVF. A brood of three would mean starting by age 23 to have the same chance of success. Wait until 35 and the odds are 50:50 (see 鈥淲hen to get started鈥�).
The suggestions are based on averages pulled from a swathe of data so don鈥檛 give a personal prediction. And of course, things aren鈥檛 this simple in real life 鈥� if only family size and feelings about IVF were the only factors to consider when planning a family. But the idea behind the model is to help people make a decision by condensing all the information out there into an accessible form.
鈥淲e have tried to fill a missing link in the decision-making process,鈥� says at Erasmus University in Rotterdam, the Netherlands, one of the creators of the model. 鈥淢y 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.鈥�
It鈥檚 a scenario that will be familiar to many; the age at which people have their first child has been creeping up over the last 40 or so years. For example, the average age at which a woman has her first child . , the birth rate for women in their 20s has hit a record low, while the figures for those over 35 have increased over the last few decades.
The decision is more pressing for women thanks to their limited supply of eggs, which steadily drop in quantity and quality with age. Female fertility is thought to start declining at 30, with a more significant fall after the age of 35.
Men are thought to have more time. 鈥淲e do know that there are male age effects, but they don鈥檛 kick in severely until a man is well into his forties,鈥� says , professor of andrology at the University of Sheffield in the UK.
鈥淚f you are relaxed about having 3 kids you can wait until 35, but you鈥檝e got to start early to be certain鈥�
The new model incorporates data from studies that assess how fertility naturally declines with age. The team took information on natural fertility from population data collected over 300 years up to the 1970s, which includes data on 58,000 women. While such , it represents the , says Habbema.
鈥淲e need data from populations in which couples try to have as many children as possible, and these populations are scarce,鈥� he says. Figures taken from hundreds of years ago are consistent with those taken more recently, he adds.
Surprising results
The model also includes information on IVF success rates for women of various ages based on 2013 figures from the Netherlands (Human Reproduction, ).
One thing it doesn鈥檛 account for, however, is the age of the prospective father. While older men are known to be more likely to pass on genetic mutations that increase a child鈥檚 risk of conditions like schizophrenia, age doesn鈥檛 seem to strongly affect a couple鈥檚 fertility until the father is in his late 40s. 鈥淥ur results are generally valid for couples where the man is not more than 10 years older than the woman,鈥� says Habbema. Pacey agrees that this is reasonable, and says that the model is 鈥渁s good as it can be鈥�.
The model is based on averages so won鈥檛 apply to every woman on an individual basis as there is a lot of variation, but it could be very helpful, says at New York University Langone Medical Center. 鈥淚t makes explicit certain statistics that don鈥檛 sink in for many people,鈥� he says.
Some of the results may come as a surprise. For example, pregnancy remains an option for women in their early 40s 鈥� with the chance of conceiving about 50 per cent. At the other end of the spectrum, the early age at which the model suggests you should start having children if you want a 90 per cent chance of having three 鈥� 23 鈥� may be a shock to a generation who are waiting until their late twenties and early thirties to even consider the prospect.
On reflection, however, the figure makes sense, says Pacey. 鈥淵ou鈥檝e got to factor in that people don鈥檛 necessarily have children in quick succession,鈥� he says. 鈥淲hat it is saying is that if you鈥檙e relaxed about having three children, you can wait until you鈥檙e 35, but you鈥檝e got to start early to be certain.鈥�
鈥淚n general, young people are very optimistic about their reproductive potential,鈥� says at the Karolinska Institute in Stockholm, Sweden. 鈥淭hey also have a lot of faith in reproduction technologies 鈥� there is a strong belief that if you can鈥檛 get pregnant naturally, there is always IVF, although it is far from a guarantee.鈥�
鈥淭here is a strong belief that if you can鈥檛 get pregnant naturally, there is IVF 鈥� but it鈥檚 no guarantee鈥�
According to the model, IVF only increases the upper age for starting a family of any size by a few years. 鈥淚VF has limited impact, and that might surprise people,鈥� says Habbema.
Habbema admits that other factors will influence decisions made by potential parents, such as their career and relationship stability, and the available childcare resources. 鈥淚t鈥檚 not easy to make recommendations,鈥� he says. 鈥淚 hope the model will play a part in making decisions easier.鈥�
Women in their 30s who want to have children needn鈥檛 worry yet, says Keefe. 鈥淪ome might think: 鈥榦h my gosh, I have to get started鈥�, but for many women that鈥檚 not true,鈥� he says. 鈥淔or women at the age margins, this could help nudge them one way or another, but we don鈥檛 want to force people to change their lives.鈥�
Pacey thinks the table should be widely circulated. 鈥淭he table ought to be photocopied and put up on the clinic wall,鈥� he says. 鈥淲e should also be aiming this at sixth formers [college students] and university students, so that they鈥檙e aware of how to plan their life.鈥� The best way to inform both young men and women, without pressuring or scaring them, might be to integrate fertility awareness into lessons on contraception that are routinely delivered at schools.
Such education programmes are being launched in Sweden, says Waldenstr枚m, and the British Fertility Society is planning to run a similar scheme in the UK.
鈥淲e haven鈥檛 got a time machine we can put people in鈥� that鈥檚 just a blunt reality,鈥� says Pacey. 鈥淓veryone thinks they can wait 鈥� this shows that you can鈥檛.鈥�
Leader: 鈥�IVF can be both a blessing and a curse鈥�
Expert鈥檚 view: We need to get the message right
, chair of the British Fertility Society
The information captured in the fertility model is extremely important to have out there. There鈥檚 been a lot of publicity recently about the decline in fertility with age 鈥� not all of it well informed. This is such an emotionally charged subject with such fundamental consequences, we need to get the message right.
In June, for example, one scientist suggested that . But this doesn鈥檛 guarantee a family 鈥� eggs don鈥檛 always freeze well, and you need to freeze quite a few to give yourself reliable insurance.
It鈥檚 also been suggested that . That鈥檚 even more ludicrous, because while male fertility falls with age, the effects don鈥檛 kick in until the late forties.
Young people today expect to have complete control over their life. The messages about unwanted pregnancy are clear 鈥� you can control that with contraception. But when it comes to getting pregnant things are less clear. For most people, it鈥檚 not as simple as coming off the pill.
It is our duty to educate people about the decline in fertility with age. There is also a case for providing fertility checks to couples. At the moment, such tests aren鈥檛 widely available to healthy people, but I don鈥檛 see why they shouldn鈥檛 be.
Couples need support so they can start their families early. Women who have children in their 20s are more likely to achieve their desired family size but can also expect lower lifetime earnings than women who start later. We need to ensure women aren鈥檛 disadvantaged at work, and sort the lack of childcare facilities so we can enable young couples to establish their careers and families at the same time.
As told to Jessica Hamzelou
This article appeared in print under the headline 鈥淭he fertility calculator鈥�
