Your Baby’s Development
Your baby now weighs about 3.9 ounces (110 grams) and measures about 4.7 inches (12 cm) in length from crown to rump. Your baby can hold his or her head erect, and the development of facial muscles allows for a variety of expressions, such as squinting and frowning.
Between weeks 16 and 18 of pregnancy, your health care provider may offer you the maternal blood screening test, also known as a “triple marker” test or “triple screen,” which measures the levels of alpha-fetoprotein (AFP), a protein produced by the fetus, and the pregnancy hormones hCG and estriol in the mother’s blood. The results of the triple marker test can tell moms whether their babies are at risk for (not whether they have) neural tube defects such as spina bifida or chromosomal abnormalities such as Down syndrome. Out of every 1,000 women who take the test, about 50 will have abnormal results, but only one or two women will actually have babies with a problem. Talk to your health care provider about the risks and advantages of this test.