Answer

Internal ultrasound examinations are sometimes used in women to examine the uterus (womb) and ovaries. You will be asked to lie on your back while a thin ultrasound probe is passed gently into your vagina. (http://www.surgerydoor.co.uk)

With regards to your question, as it entails something being inserted into ones private parts, the fast will break. (Fatawa Hindiyyah p.207 v.1)

Only Allah Knows Best