Otumoetai mum Jodi Nicols knows all too well that plenty of twins are born in New Zealand.
Whenever she takes her identical girls, Zoe and Mia, out she is stopped by other mums who have had twins.
In the Bay of Plenty, 146 twins were born last year, compared with 86 in 2007.
Last year 1774 twins were born in New Zealand, compared with 984 in 1980, but the rate has started to level off in recent years as fertility treatments are becoming more refined.
Mrs Nicols conceived Zoe and Mia at age 28, and said her natural pregnancy was probably more down to family genes than age.
Her great-grandmother was a twin, and most of her great-grandmother's seven siblings and their children went on to have twins.
Mrs Nicols said she was stopped constantly when out with her twins, who were born last year: "People are either a twin or have had twins."
The odds of having twins again are high and Mrs Nicols said she and husband Shaun, would wait and see before deciding whether to increase their family.
Identical twins develop after one zygote splits and forms two embryos.
This month the US National Centre for Health Statistics released data which showed the birth rate of twins surged 76 per cent in the past 30 years. It went from a birth rate of 19 twins in 1000 US births in 1980 to 33 per 1000 births in 2009.
However, Statistics New Zealand data shows that twin birth rates in New Zealand since 2000 have stayed at about 27 to 30 twins in 1000 births.
Emma Parry, spokeswoman for the Royal Australian and New Zealand College of Obstetrics and Gynaecology, said the plateau could be explained in part by advances in fertility treatment.
In the early days of IVF, two or three fertilised eggs were put back into a patient's uterus to maximise chances of a baby.
But research has since shown that the chances of having a baby are as good if just one embryo is used, which in turn reduces the chance of multiple births.
Roz Irwin, chairwoman of the Tauranga Multiple Birth Group, which has 60 registered families, said with her twins it had been a case of second time lucky with IVF treatment during a period of 12 months.
The now 42-year-old was 38 when she had twins Kody and Samantha with husband, Ken, then aged 59.
Mrs Irwin said her husband had a vasectomy 30 years earlier and had older children from his first marriage. Due to Mrs Irwin's age, two embryos were implanted and she and her husband got "everything we basically wanted" with twins of each gender.
They wouldn't change twins for the world, she said.
Twins born in the Bay of Plenty
Figures are for year ended September. - Statistics New Zealand.