Ok mommies of twins when did you find out the sex of the babies. My little sister will be 18 weeks…

Ok mommies of twins when did you find out the sex of the babies. My little sister will be 18 weeks and I guess she called and asked if tmrws appt was going to be an ultrasound since they normally monitor super close since she's high risk because of the twin shock something or another where they share placenta and one baby gets more blood than the other but I guess she's not getting one this time and she was hoping to get genders.