kembabe- the placenta starts forming very early on but around week 12-14 it starts producing hormones by itself and completely nurturing the baby.
If you only have one ultrasound, around week 18-22 you would be able to know the sex of the baby.
early on.
im most cases yes one ultrasound is enough to determine the sex of a child...however thats around 20 weeks and you should be having more than one ultrasound