When will they use a tummy probe ultrasound?

I usually have to have a transvag ultrasound due to having a retro grade uterus, Im currently 14 weeks and was wondering when the baby would be big enough to use a trandsabdominal probe? We would like to find out the sex at 16 weeks, but not sure they will be able to see with the tummy probe and they dont offer transvag for gender determintaion at the place we are going. Thanks for any info!|||Usually they will do the abdominal ultrasound once you're in your second trimester. I went in at 13 weeks, and they did it both ways. By 16 weeks, I highly doubt they would do a vaginal ultrasound. At 16 weeks, you may not be able to tell the sex of the baby. It could be too early, especially if it's a girl. My cousin and I both had ultrasounds at 18 weeks, and they immediately told me I was having a boy. They told my cousin it was too early to tell, and she ended up having a girl. You're more likely to find out if you are having a boy. If it's a girl, it might be too early for them to make a positive conclusion. It also depends on the baby's position. Best of luck!