A new study by University of New South Wales medical researchers shows that certain types of assisted reproductive technology used to treat infertility lead to more male than female babies being born.
The research team examined the effects of two different types of ART procedure: 'standard' IVF and ICSI (intracytoplasmic sperm injection, where the sperm are not motile and have to be injected directly into the egg), the stage of embryo development at the time of transfer - blastocyst (four days after fertilisation) or cleavage (two to three days after fertilisation), and the type of embryo used (fresh or thawed).
The study, published in BJOG: An International Journal of Obstetrics and Gynaecology, was undertaken to find out if there is a link between the type of ART used and the sex ratio at birth (also known as the secondary sex ratio - SSR), defined as the proportion of males in all babies born alive.
It found the SSR for babies born from single embryo transfer (SET) was 51.3%, which is comparable to the SSR for the general Australian population (51.5%). However, the results also show that specific ART regimes do indeed influence the SSR. There were fewer male babies born after ICSI SET (50%) and more after IVF SET (53%). The stage at which the embryo was transferred had even more effect; 49.9% for cleavage stage SET and 54.1% for blastocyst SET.
The highest SSR was in the IVF SBT transfer group - 56.1% males - and the lowest in the ICSI cleavage SET group - 48.7%.
Jishan Dean, co-author of the study from the Reproductive and Perinatal Epidemiology Research Unit at UNSW said, "This is the first national population-based study to assess the impact of ART procedures and treatment practices on the human sex ratio at birth.
"The results from this study demonstrate that a particular ART procedure or treatment course can alter the probability of having a male baby from the natural sex ratio at birth in Australia of about 51.5%, to a low of 48.7% (a decrease of 2.8%) or a high of 56.1% (an increase of 4.6%), depending on the procedure used.
"At an individual patient management level the type of clinical problem decides the most appropriate ART management plan, whether it is IVF or ICSI. The result of this study should therefore not be used as a de facto tool for sex selection," she said.
Study co-author, Professor Michael Chapman, from the School of Women's and Children's Health, said that with only 3.5 percent of babies born through assisted reproductive technology, the social impact of the bias would be negligible.
The real area of interest was in discovering why the differences occurred.
"This study provides impetus for further research into the underlying causes and or associations which determine the survival of different sexes of embryos in pregnancy."
The full release is available from the Journal's website.
Media contact: Steve Offner,UNSW Media | 02 9385 8107 | 0424 580 208