Many parents are keen to know the sex of their baby before its born. By the time of your 20-week scan its fairly easy to tell the sex, as long as the person doing the scan, called the sonographer, gets a good view. The difference between boys and girls is fairly obvious at this stage. As your pregnancy progresses, the difference becomes even clearer and, provided there is plenty of amniotic fluid around your baby and it doesnt have its feet tucked up between its legs, a third trimester scan can usually show its sex.
However, in the early weeks its not so easy. The sex of a baby is genetically determined at conception, but during the early development of embryos, they all look the same.
All embryos have a small bud or swelling. It's known as the genital nub or protuberance. If you are having a boy, testosterone starts being produced when you are about seven weeks pregnant, prompting the bud to grow and develop into a penis and scrotum. In a girl the genital nub will become the clitoris and labia.
This is a gradual process and it is only from about 11 weeks that it becomes possible to see any difference between the sexes. By this stage, all babies have something sticking out. In boys, it tends to point upwards at an angle of more than 30 degrees from the spine. In girls, its more horizontal to the body, at an angle of less than 30 degrees. The baby needs to be lying on its back for the sonographer to see this.
In fact, studies show that it's a pretty hit and miss affair. Early research showed that, in babies that were lying in a position to see, very experienced sonographers using top-of-the-range scan machines got the sex right in only 70 per cent of cases at 11 weeks, and in just over nine out of 10 cases at 12 weeks.
In a more recent study, sonographers could only correctly identify the sex in 46 per cent of babies at 12 weeks and 80 per cent at 13 weeks.
However, its very unlikely youll get to know the sex at a routine dating scan. Most scan machines aren't high-tech enough to see, and there won't usually be time for the sonographer to wait for your baby to be in the right position. By 13 weeks, your baby will be able to curl up and perform acrobatics so getting the right angle can be very difficult.
Being told the sex and then finding out later that it was wrong can be very distressing. Unless you need to know the sex because you have a family history of gender-linked genetic problems, its best to wait until your mid-pregnancy detailed scan. The chance of getting the sex right then is a lot higher.
Hope this helps a bit more??!!!