The age women need to start conceiving if they want 3 or more kids.

Want a big family? It might already be too late, according to experts.

A newly released study on women’s fertility is half fascinating, half terrifying.

The Dutch study, published last month in the journal Human Reproduction, is all about how fertility declines with age. And it carries some very specific advice about when you should try for your first baby.

If you’re dreaming of more than two kids, it basically recommends you start… well, in the past. (Sorry, life plans.)

Researchers studied 58,000 women over three centuries and found that those who want three or more kids without IVF, should start conceiving at 23.

Doing so will give them a 90 percent change of fulfilling a three-kid quota, apparently.

Those wanting just one or two kids can wait a while: The study concluded that “without IVF, couples should start no later than age 32 years for a one-child family, at 27 years for a two-child family, and at 23 years for three children.”

(By the way, the model assumes that couples “start trying for the next pregnancy 15 months after the birth of a child”. So if you want kids a few years apart? You’d better factor that in, too.)

The model was created to help women make decisions about their fertility by condensing relevant information into an easy-to-read graph.

Dr Dik Habbema from the Netherlands’ Erasmus University told New Scientist it was intended to “fill a missing link in the decision-making process” for people trying to decide when to have babies.

“To our knowledge, this is the first time that the maximum female age for starting a family has been estimated,” Dr Habbema and his colleagues wrote.

Mia: For every woman struggling with infertility who feels like a failure right now.

Since the average age of first-time mums in Australia is currently 28, it seems some of us are leaving it later than recommended (unless most women want one kid or none at all, that is).

The researchers suggested women’s overconfidence in reproductive technologies may be to blame.

“From fertility-awareness studies and population surveys, we know that most young people are too optimistic about their chances to conceive spontaneously after age 35,” they wrote.

“Also, supposedly due to the ‘miracle’ stories in the media about 60-year old women who became a mother after IVF, young people tend to overestimate the effectiveness of IVF.”

University of Sheffield andrology professor Allan Pacey told New Scientist the study’s emphasis on not delaying conception was so important, it should be distributed to high school students.

 Related: The worst thing you can say to a woman trying to get pregnant? Hurry up.

“The table ought to be photocopied and put up on the clinic wall,” he said. “We should also be aiming this at sixth formers and university students, so that they’re aware of how to plan their life.”

Fertility expert Dr Kylie de Boer of Bump clinic agreed with aspects of that message.

“I would support education around the effects that age has on your fertility, both for men and women. I mean, people are very informed nowadays and it’s important that they get the right information,” she told Mamamia.

She warned, however, against people getting overly “hung up on numbers”.

“Every individual is different, but I would support the gist of this message definitely getting out,” she said.

In slightly better news for older women who want large families, the study also found an average 40-year old woman still has a more-than-50 percent chance of spontaneously conceiving a “live-birth pregnancy”.

A woman who wants a child and is open to IVF still has a 90 percent change of success if she starts at age 35, the study said.

Dr de Boer told Mamamia that having babies early “doesn’t work for everyone for a whole host of reasons”. She women shouldn’t “panic” if they don’t conceive early.

“You’re still very fertile in your 30s, and that’s what I mean about getting hung up on statistics. But fertility does start to decline in your 30s, and it declines rapidly from 37,” she said.

“So there’s no reason to panic but it’s important to have in the back of your mind, ‘the older I get, the harder it is to have a healthy pregnancy’.”

Some celebrities who had babies in their 30s and beyond (post continues after gallery):

So, there you have it. While there’s no need to freak out, some experts want us to get cracking — like, now — if a large family is on the agenda.

We don’t know whether to swear, cry, or just immediately get busy.

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