As a fertility specialist, Dr Mary Birdsall has difficult and emotional conversations with couples desperately wanting a baby on a daily basis.
"We can help anyone of any age have a baby if we sub in someone else's eggs but most people want to use their own eggs. Donor eggs whilst always an option - is always option B," says Dr Birdsall.
In the 1970s the median age of a woman giving birth was 25 - now it's about 30.
Dr Birdsall says from a biological perspective nature designed women to have babies in their early 20s but as a society, we're doing it later.
Fertility New Zealand, a registered charity which helps those with fertility issues says people who want to become a parent in the future should plan for their last-child, not first.
"A diagnosis of infertility can be incredibly distressing and challenging on many levels. It's important to remember that men are just as likely as women to have a diagnosis of infertility. "We encourage people to seek information and support, make a plan, and take control as much as possible. Everyone who is trying to become a parent can help optimise their chances through lifestyle changes and seeking help where appropriate," says Fertility New Zealand Chair Juanita Copeland.
As part of the newshub.co.nz series on women's health, Dr Mary Birdsall has given the following advice for women in their 20s, 30s, and 40s who want to someday have a family.
20s
"Often women in their twenties aren't wanting to start a family, they're just wanting to know what they should be doing. My advice to women in their 20s is to look after their fertility, protect themselves against STIs like Chlamydia and Gonorrhoea.
"They shouldn't be taking up smoking, drinking heavily. What would be great for all women in their twenties to do is to get a blood test to measure their AMH (Anti-Mullerian Hormone). "Then they know how long they've got and then they can plan their lives."
30s
"Women in their thirties should be starting. They should have hunted down 'Mr Right' or they should be thinking about putting some eggs in the freezer or thinking about a sperm donor.
"Women in their thirties should be getting on with it."
If you're not pregnant after a year of trying, seek medical advice.
40s
"Women in this age group should be seeking fertility advice to find out where they're exactly at as their time is rapidly running out or maybe run out.
"They should be asking: 'have I got some eggs left, what should I be doing?' There are always options with donor eggs if needed.
"The average age Kiwi women have their last baby without any help is 41. It's always surprising to hear that."
