Research published in BJOG: An International Journal of Obstetrics and Gynaecology, suggests certain forms of assisted reproductive technology could lead to a male / female imbalance. According to researchers, certain types of single embryo transfer (SET) are more likely to result in the formation of a male child than a female child.

Included in the study were health records of women receiving single embryo transfer between 2002 and 2006 in Australia and New Zealand. A total of 13,368 infants were born to 13,165 mothers. The two forms of assisted reproductive technology (ART) studied were IVF and ICSI. ICSI stands for intracytoplasmic sperm injection, during which immobile sperm is injected into the egg. Researchers were looking for a link between ART and SSR or secondary sex ratio or sex ratio at birth.

Overall, the SSR from single embryo transfer resulted in 51.3% males. This is comparable to the sex ratio of Australia which is approximately 51.5% male. When the methods of ART were broken down, significant differences occurred between types of ART used and for the length of time, post fertilization, waited before implantation.

Blastocyte is the term for eggs four days after fertilization. Cleavage is the term for eggs two to three days after fertilization. For the sake of study results, we will denote these as “B” and “C”. Percentages refer to male infants:

  • ICST SET = 50% males
  • IVF SET = 53% males
  • IVF SBT = 56.1% males
  • ICSI SCT = 48.7% males

Researchers note this is the first study where the type of ART procedure used and age of the fertilized egg can alter the gender outcome of a pregnancy.

Source: Dean J, Chapman M, Sullivan E. BJOG: An International Journal of Obstetrics and Gynaecology. 29 September 2010.