My Pregnancy Week 18
Your baby is now roughly the size of a bell pepper. He is about five and a half inches long, and weighs almost seven ounces now.
If you are having a boy, his genitals are now noticeable, if he isn’t curled up and hiding them during the ultrasound. If you are having a girl, her uterus is fully formed and in place, along with her fallopian tubes.
Your baby’s skeleton, which up until this point has been made up of flexible cartilage, is now hardening into bone. Myelin, a protective layer covering his nerves, has begun to form. Myelin plays an important role in the communication between neurons, and it will continue to develop through his first year of life.
At 18 weeks, your baby’s skin is still thin and transparent, so to help protect her, something called the vernix caseosa develops. This is a greasy, cheese-like substance that not only insulates her developing epidermis and dermis from the amniotic fluid; it also makes her nice and slippery for an easier delivery.