While the external genitalia of your baby starts to develop at around 12 weeks, the earliest time we are able to carry out an accurate gender determination is around 16 weeks of pregnancy. When it comes to 3D maternity ultrasound, we constantly strive for complete customer satisfaction, so to avoid erroneous determination, we would advise waiting until you are at least 16 weeks pregnant to come in for the gender reveal. The bigger the baby is the more accurate the gender determination will be.