15 weeks -you've probably gained between 2.2kg and 4.5kg, your baby weighs only about 70g. He measures nearly 9.1cm, crown to rump. your tiny tenant frequently gets the hiccups, which babies learn to do before breathing. Babies don't make any sound because their windpipe is filled with fluid rather than air.Your baby's legs are growing longer than his arms now and all his joints and limbs can move. His genitals may be developed enough to show on an ultrasound scan.