The number of Australian and New Zealand women giving birth to twins after becoming pregnant with the help of assisted reproductive technology has fallen dramatically and is expected to drop even further.
The rate of multiple births from assisted reproductive technology cycles - such as IVF - fell from more than 14 per cent in 2005 to just over 8 per cent in 2009, according to a report to be published today by the Australian Institute of Health and Welfare.
Fertility Society of Australia president Peter Illingworth expected the multiple birth rate to keep falling and said it could be explained by the move toward transplanting a single embryo into a woman instead of several.
''Other countries do put back more embryos and Australia has been fairly unique in the number of embryos replaced so that we've moved very smoothly and steadily over the last 10 years to achieve singleton pregnancy rates which countries like the UK can only dream of,'' Associate Professor Illingworth said.
The reduction in multiple births had been achieved while pregnancy rates from assisted reproductive technology cycles remained steady at about 23 per cent.
The report showed that older women who used assisted reproductive technology were less likely to have a baby than younger women.
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For women who used their own eggs, the live delivery rate was almost 27 per cent for cycles in women aged 30 to 40 years, but less than one per cent for women aged over 44 years.
More than 20 per cent of clinical pregnancies from embryo transfer cycles in 2009 resulted in ''early pregnancy loss'' at less than 20 weeks gestation and less than 400 gram birthweight.
More than 9 per cent of early pregnancy losses were due to miscarriage, 3.3 per cent due to the aborting of one of more foetuses in a multiple pregnancy or termination of pregnancy and 6.6 per cent due to ectopic or heterotopic pregnancy.
In 2009, 1.5 per cent of all babies born following embryo transfer cycles were stillborn or died within 28 days of birth.
Professor Illingworth said IVF pregnancies had a slightly higher risk of some problems but the reasons for this were not clear.
''We know that most of that is down to twin pregnancies but even with singleton pregnancies there is a small increase in perinatal losses,'' he said.
''There's discussion about whether that's a consequence of the IVF stimulation, or whether women who struggle to get pregnant naturally are always going to end up having higher perinatal mortality.''
The number of women using assisted reproductive technology grew by almost 50 per cent between 2005 and 20009 to 70,500.
But Professor Illingworth said IVF treatment cycles had fallen since 2010 when changes to the Medicare Safety Net were introduced. ''That reflects the fact that the Medicare Safetynet changes were flagged about half way through 2009 and many women chose to do their IVF earlier in 2009, rather than carrying on into 2010,'' he said.
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