Transvaginal at 10 weeks 5 days ?

I went in for my 2nd doctors appointment today. She said today she would be able to see the baby with an ultrasound on my stomach. She tried and couldn’t see the baby. It was scary and she couldn’t say why that was the case . Then she did a transvaginal ultrasound and we saw the baby , and heartbeat and size were just as expected. What a relief ! Has this happened to anyone else ?? My doctor said it wasn’t common to need transvaginal at this point in the pregnancy but not to worry because Baby looked great. Any ideas why the other ultra sound couldn’t pick up the baby ?