Your Baby's Development By this week, some fine hairs have
developed on your baby's face. This soft colorless hair is
called lanugo, and it will eventually cover most of your baby's
body until it is shed just before delivery. By now, your baby's
genitals have fully developed, though they may still be
difficult to detect on an ultrasound examination. In addition,
your baby starts to produce thyroid hormones because the thyroid
gland has matured. Your baby now weighs about 1.6 ounces (45
grams) and is about 3.5 inches (9 cm) long from crown to rump.
Under certain circumstances (for example, if you're older than
35 or if your screening tests indicated that there may be a
problem with the fetus), your health care provider may discuss
amniocentesis with you. Amniocentesis is a test usually done
between 15 and 18 weeks that can detect abnormalities in a
fetus, such as Down syndrome. During this test, a very thin
needle is inserted into the amniotic fluid surrounding the baby
in the uterus and a sample of the fluid