The earliest you can have a gender scan is 16 weeks exactly. Before this time (even 15 weeks and 6 days) sexing baby is unreliable and we always aim to provide you the right answer! Why does 24 hours make such a difference? Good question. Baby actually grows the fastest between weeks 15-16 so every day makes a huge difference. Just think, at this stage we are looking for girl/boy bits that are smaller than your little finger nail!
At 28-32 weeks your baby has a chubby face and for pics of facial characteristics this would be the best time. Please be aware that if you wait too late for your 4D scan baby might be too big and there may not be enough fluid in front of baby’s face to get great images.