At 17-18 weeks of pregnancy, your baby is about the size of a turnip, growing to the size of an artichoke (about 5-6 inches in length).
Their facial features are continuing to become more defined, and they can make more facial expressions, which you may be able to catch on certain types of ultrasounds. Just as with weeks 15-16, your baby’s skeletal system is continuing to become harder and create more structures. The circulatory system is also continuing to develop, with blood vessels becoming more visible.
This is the point where vernix, a cottage cheese-like substance, starts to form on your baby’s skin. Similar to the lanugo hairs, the purpose of vernix is to protect your baby’s skin from the amniotic fluid surrounding it - after all, that is a lot of liquid to be in all of the time.