Depending on the species, there are different mechanisms to determine the gender of the baby to be born. In some reptiles, the temperature at which eggs are incubated determines the gender of the brood; in some fish specie , sex at birth is not important as they have the ability to change the gender when it is required; in humans, gender is determined genetically .

While there are similar likelihood that an embryo has implanted genetic information to form a male or a female, during pregnancy, there would be some increased survival of males. The World Bank data shows that the male/female ratio at birth is 1.07 , which means that every 100 females 107 males are born ( or what is the same, that 51.7 % of births were male and 48.3% are females), which remains a constant tendency in all locations from which data is obtained.

A recent published by Maalouf et al in the journal Fertility and Sterility evaluated more than 100,000 children born in the UK from assisted reproduction treatments made ?? there between years 2000 and 2010. They showed that the type of treatment could make an impact on the male/female ratio of newborns, noting that in IVF (in vitro fertilization) male proportion was 52.1 % , whereas when it is ICSI ( intracytoplasmic sperm injection), the proportion was 49.3% . Another aspect that seems even more relevant is the stage of transfer, noting that when transfer is performed in blastocyst stage, for both types of treatment, the proportion of male would increase by about 6%.
While these data do not seem relevant to everyday decisions, these are important aspects to be assessed periodically when viewed from a broader perspective and the long- term impact that it could have  on the society.