How is my baby growing and developing during week 18?

In week 18 of pregnancy, your baby is now nearly twice as large as it was one month ago! Weighing about 7 ounces, your baby's bones, even its tooth buds and jaw, are continuing to harden. The windpipe has developed and its two bronchioles - airways - one for each lung are continuing to grow. Your baby's outer ears are almost fully developed, and although the inner ears are still immature, your baby may be able to hear your heartbeat! Its genitals are developing, and during an ultrasound your doctor may be able to see whether your baby is a boy or a girl.