In general, the male to female ratio is commonly assumed as 105 boys to 100 girls. It is believed that boys outnumber girls at birth to compensate for the higher mortality of baby boys.
The study conducted at Michigan State University in East Lansing showed that woman's chances to give birth to a boy are lower, if she conceived a baby using intracytoplasmic sperm injection (ICSI).
During the ICSI, sperm is injected directly into an egg. In case when one or several embryos develop, they are then placed into woman's uterus. The ICSI procedure is commonly performed if a couple faces male fertility issues like low sperm count or poor sperm quality. It can also be recommended for couples with unexplained infertility.
The study analyzed the data from 15 000 babies born in the US in 2005 through assisted reproduction technology. Scientists revealed that fewer boys were conceived when a woman used ICSI technology. This was particularly true if the procedure was done using more mature embryos to be transferred to a woman. This gives an opportunity to place fewer embryos and lower couple's chances of having multiple births.
The results of the study showed that for couples using ICSI treatment, the chances of conceiving a boy were less than 50 percent, if compared to the average 52,5 percent of boys, who were conceived naturally.
It is not clear why in vitro fertilization treatment results in fewer boys births. Scientists say that while the ICSI technology is unlikely to cause any concern for public health, it is still advisable to use ICSI only if it is medically necessary to avoid the imbalance of male to female ratio.The study was published in the recent issue in the journal Fertility & Sterility.