The number of women having babies after the age of 40 is now almost as high as those under 20.
Many women are choosing later-life motherhood due to studies, careers, finances and finding Mr Right.
But if you are planning on waiting there's a blood test which could tell you how long you've got.
While many women can conceive naturally after 40, 10 percent of women experience a faster decline in fertility. One in 100 will go through menopause at the age of around 40.
"The problem is that often there's no outward sign to that individual woman that her fertility's declined, often until it's too late," say Fertility Associates Medical Director, Dr Simon Kelly.
Dr Kelly says the average age of a woman approaching Fertility Associates is 37, but he says women should be finding out about their fertility much earlier.
He recommends having a blood test in your 20s or early 30s which can tell you how many eggs you have left and how soon they'll run out.
The AMH test measures the anti-mullerian hormone.
"This is a hormone that is produced by every egg that a woman has, so if I measure a woman's AMH result it gives me a very clear idea of how many eggs she has," says Dr Kelly.
"It just puts them in the picture as to where their fertility's at, maybe allows them to make some decisions."
It gives women the option of having children earlier or freezing eggs for future use.
The test costs around $80 to $110 and you can get it through your GP.
The number of women having children under the age of 20 has dropped dramatically - halving the past eight years - while the number of women giving birth over the age of 40 remains high.
In New Zealand, 2388 babies were born to women over the age of 40 in the year to September 2016.
Maylin Coordes hadn't planned to leave motherhood so late.
"It was just finding the right person, and I didn't meet him until later in my life."
"We started trying when I was 32, 33," but she says nothing happened. "It was unexplained infertility."
After undergoing IVF, Maylin had a little girl at the age of 37, and baby Liam came along when she was 41.
But she knows she was lucky.
"If I had to do it again, I would have looked into the options earlier."
A blood test in your 20s could save you heartache in your 30 and 40s.
If you are planning on waiting to become a mum, here are five things you need to know:
- One in 10 women experience menopause early - around age 45 instead of 50. One percent of women enter menopause by the age of 40.
- Women who lose their fertility earlier either have fewer eggs to start with or lose them faster.
- A blood test can estimate your 'ovarian reserve', the number of eggs left in the ovary. The AMH test is not publicly funded. It costs around $100. Ask your doctor for more details.
- The AMH test is useful to identify whether you should plan on having a family sooner by identifying those who are likely to lose their fertility earlier than average.
- Although AMH can help determine your fertility prognosis, family history and lifestyle are also important factors.