We are very close to be able to determine, before a baby is born, if he/she is gay. There are two gene variants that have been discovered to be very common in gay men.
It has been known for many decades that sexual orientation is partially heritable. It has been discovered some genetic variations in the X Chromosome in men, specifically a region on the chromosome 8 that could point to the fetus being gay.
It is not in the so distant future where parents will be able to execute a DNS test on the fetus and determine it’s sexual preference. Given the wide acceptance of abortion these days, this information could be very well used to kill the fetus before is born.