When can i know exactly my baby's sex as i am 19 week pregnant and my doctor said that it seems girl but i am not sure till now. why is not clear?

Fetal Gender: Because the pictures are made by sound waves. There is never 100% good visibility on an ultra sound. I would bet that the doctor is right! congratulations you are having a girl.

Thanks for asking!: While a baby's penis or vulva begins forming as early as 6 weeks, boy and girl babies look very similar on ultrasound until about 14 weeks, and it can still be hard to tell them apart for several weeks after that. By 16-20 weeks, an ultrasound technician should be able to identify the sex if the baby is in a position that allows the genitals to be seen, but 20 weeks is the best time.

Bashful: Fetuses aren't always most cooperative for ultrasounds. They can be "bashful" and not display their genitalia clearly for ultrasound to determine gender. If penis is visible, it's obviously a male. But if not visible, perhaps he's just "bashful" & ultrasound tech is unable to visualize it.