Hollywood big names are leading the trend to have children after age 40, and though new figures prove Kiwis too are starting parenthood later, experts are warning those who delay they face "a lot of anguish".

Madonna, Nicole Kidman and J K Rowling had babies in their 40s and recently John Travolta's 47-year-old wife Kelly Preston revealed a baby bump. But it's not just the rich and famous having children over the age of 40.

Ministry of Health data revealed that last year 2479 Kiwis gave birth aged 40 years or over - up from 1458 births in that age group a decade earlier.

Fertility doctors Richard Fisher and Guy Gudex were not surprised by the statistics; a third of Fisher's clients undergoing IVF were in their 40s, while Gudex said two-thirds of his private clients were around that age.

Fisher said some women were very lucky and could conceive over 40, but he warned that was usually far from the norm. The older a woman was, the lesser the chance of conceiving. The risks of having abnormal eggs or miscarriages also soared with age.

"There's only a 6 per cent chance per month of getting pregnant aged 40," said Fisher, adding the optimum time for conceiving was in the 20s to early 30s.

Laura Carr, spokeswoman for the Nurture Foundation - a charity dedicated to funding research into infertility, miscarriage and pregnancy complications - urged women not to leave parenthood too late. Many who did this faced "a lot of anguish" trying to conceive.

She said some celebrities gave the impression it was easy to have a baby over 40, but the reality was they were "incredibly lucky".

Other reasons for the late leap into motherhood include women being career-driven, while some hadn't met Mr Right until their 30s.

Fisher said men should commit to their partners earlier if they wanted to be fathers. "Half of all the people we see ... there's a significant male factor."

Former Auckland cake stylist, Elish Browning, 44, had Cody 13 days ago - her third child with husband Doug Barnett. Their other two children were four and three.

She said financial reasons were a big reason in putting off having a family, but being an older mum meant she had more patience and was "happy to take the time to be a parent".

Former Auckland accountant Carla Hood, 47, had two of her three children when over 40. She had loved her career and had not thought much about children - until she was 36 and met electrician Ian Bull.

Second family idea born of tragedy

Older mums can be better mums because they're more relaxed, they've got travelling out of their system and "they're happy to settle down and do the family thing".

This is according to Lyn Mason, who made history in 2002 by becoming New Zealand's oldest mum, then aged 53, by giving birth to son Dean - now 8 - thanks to a gift of donor eggs from a friend. The Waikato stay-at-home mum, now 61, and husband Ian, 62, who works for Fonterra, also used the same donor's eggs to have Celine, now aged 6.

They yearned for the two treasured children after they tragically lost their eldest daughter Kylie in 2000, aged 12, in a car crash, along with Lyn's mum Mary.

"I think we would've been pretty sad people if we hadn't created a new family," says Lyn.

"They're such loving kids and we're so fortunate."

Lyn says it does not matter what age women are when they choose to become a mum, it's an individual choice, and she supports others following in her footsteps. She and her husband are in good health and are just enjoying each day.