hope this answers your question :?
http://islamqa.com/en/ref/6201/ultrasound
Ruling on finding the sex of the baby in the mother's womb before its birth by doing ultrasound and other medical equipments.
Praise be to Allaah.
We put this question to Shaykh Muhammad ibn Saalih al-‘Uthaymeen, may Allaah preserve him, who answered as follows:
There is nothing wrong with that, unless it involves great expense. It could be said that it is a waste of money because there is no need to know the sex of the baby except for the purposes of merely feeling happy because one knows whether it is a boy or a girl. If finding out could not be achieved without spending a lot of money then it is a waste of money and is not permitted. And Allaah knows best.
Shaykh Muhammad ibn Saalih al-‘Uthaymeen