The researchers reported a growing number of IVF treatments were using frozen embryos, from 39 per cent of IVF cycles in 2009 to 45 per cent in 2013.
The success of frozen embryo birthrates was put down to rapid freezing techniques known as vitrification and improved timing of the embryo transfer.
Other techniques, such as culturing embryos for five to six days to a blastocyst before transfer to a woman, with the use of pre-implantation genetic screening, had also increased over recent years.
In 2013, 5373 IVF treatment cycles were reported from NZ clinics - an increase of 3.8 per cent from the year before.
Just over 1300 babies were born after IVF treatment in Kiwi clinics over 2013 and 2014, and in both countries the rate of multiple deliveries fell to 5.6 per cent in 2013 from 8.2 per cent five years earlier.
This was one of the lowest rates in the world, and far below those in the US (26 per cent) and Britain (16 per cent).
Fertility Associates' Auckland medical director, Dr Simon Kelly, was not surprised. New Zealand had been a leader in single embryo transfer and reducing multiple pregnancies, he said, and clinics here had had "excellent" birthrates from frozen embryos for many years.
Fresh v frozen
• The birthrate in New Zealand and Australia from frozen embryo IVF transfers rose by 25 per cent in the five years to 2013, reaching the same rate - 23 per cent - as births from transfers of fresh embryos, a new report shows.
• The researchers reported a growing number of IVF treatments were using frozen embryos, from 39 per cent of IVF cycles in 2009 to 45 per cent in 2013. At Fertility Associates in New Zealand, frozen embryos now accounted for about 45 per cent of IVF cycles and their quality stayed the same whether stored for five or 15 years.
• However, age still matters. For women aged 30 to 34 using their own eggs, the birthrate per embryo transfer performed was 32.8 per cent for fresh cycles and 27.5 per cent for frozen cycles. For women over 44, the rates were smaller still at 2.3 per cent and 6.5 per cent respectively.
• A review of women who undertook their first IVF cycle in 2011 showed the best chance of success was the first treatment cycle (20.6 per cent), with the birthrate falling by 1-2 percentage points for each cycle after that.
NZ-based screening service launched
• A special service for frozen embryos has become much more accessible to Kiwi parents this week, with the launch of a pre-genetic screening partnership between major clinic Fertility Associates and Canterbury Health Laboratories.
• PGS is used to screen embryos created during routine IVF treatment, enabling those which have the correct number of chromosomes to be selected.
• Having only embryos with the right number reduces the chance of miscarriage, and the probability of a healthy live birth from an embryo transfer with PGS can be as high as 65 to 70 per cent - a rate double that without it.
• Fertility Associates' Dr Simon Kelly said having the PGS service provided in New Zealand instead of overseas reduced the price to one-third of the original cost, making it an affordable option for couples experiencing multiple miscarriages or failed implantation during an IVF cycle.
