How long until ultrasound shows baby sex? how many weeks do you have to be pregnant until an ultrasound can reveal the sex of a baby? or is it even through ultrasound that they tell the baby's sex these days?

Ultrasound : Ultrasound is pretty much the only way to determine the sex of the baby. Generally, the best time to have this ultrasound performed is at approximately 20 weeks gestation (i.e. 20 weeks following the last menstrual period). Occasionally, the sex can be determined by 18 weeks, but this is usually more difficult and there is more possibility of error. Later during pregnancy (after 30 weeks) the genitals are more developed, but the baby has also grown and has less room to spread out often making the genitals more difficult to see. For this reason, it is important not to wait too long after about 20 weeks.

Varies: Depending on your weight, if you have any abdominal scarring, and the baby's position, sometimes we can tell gender as early as 12-13 weeks. But at 16-18 weeks we can commonly tell.