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), 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 is taken and analyzed. Amniocentesis does carry a very slight risk of miscarriage, so talk to your health care provider about your concerns and the risks and advantages of the test.