Is an internal ultra sound mandatory in the first trimester?

Gwendolyn • My husband and I are first timers and were just married in July 2015!! Due date is estimating in August 2016 👶🏽🐼
Some OB's I've called insist they ONLY do internal ultrasounds which seems ridiculous to me. One, because their office should be equipped to do internal AND external. And two, because some women may be uncomfortable with how invasive they are and should have the right to opt out of them. Is this normal?