Fertility treatment may alter gender balance: study

Wed Sep 29, 2010 9:36am EDT
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HONG KONG (Reuters) - Certain types of assisted fertilization appear to result in more male than female babies being born, a large study in Australia and New Zealand has found.

The researchers have no answer why it is so, but they warn that their findings should not be exploited for sex selection.

All fertility clinics that took part in the study comply with Australia's national guidelines that ban gender selection, the researchers wrote in their findings published on Wednesday in BJOG: An International Journal of Obstetrics and Gynaecology.

Led by co-author Jishan Dean from the School of Women's and Children's Health at the University of New South Wales, the researchers studied records of 13,165 samples who underwent in-vitro fertilization (IVF).

Among women who were given standard IVF, 53 percent had male babies, while 50 percent of women who were given intracytoplasmic sperm injection gave birth to boys.

Intracytoplasmic sperm injection is done when sperm is not motile and has to be injected directly into the egg.

In standard IVF, sperm and egg are incubated together in a culture medium for about 18 hours and the egg is usually fertilized within that time.

More boys seemed to result from embryos that were transferred to the womb 4 days after fertilization (54.1 percent) compared to 2-3 days after fertilization (49.9 percent), the study found.

Over the years there has been a big increase in the proportion of IVF births.   Continued...

<p>The world's first 'test tube baby' Britain's Louise Brown, faces the media holding 13 week old twins Antonia and Henry Veary, as Professor Bob Edwards (L) looks on, during 25th anniversary celebrations of the revolutionary fertility treatment 'In Vitro Fertilisation' (IVF) at Bourne Hall in Cambridgeshire July 26, 2003. Brown joined Edwards, who along with the late Patrick Steptoe pioneered the treatment in 1978, as guest of honour at the celebrations. The Veary twins were also born via IVF treatment. REUTERS/Lee Besford</p>