Hey mama! Usually around 18-20 weeks (so around 4-5 months) kaya na makita ng ultrasound tech kung boy or girl, pero 4 months exactly might be a bit early pa, depende talaga sa position ng baby at skill ng technician! Best approach is to ask your OB kung ready na ng baby mag-cooperate sa gender reveal, kasi minsan shy talaga ang babies hehe. One of my mum friends had to go back for another ultrasound kasi hindi makita ng doctor kung boy or girl sa first one, so don't stress if you can't find out yet!