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 a second trimester screening test (known as the multiple 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. It's called a quadruple screen (or quad screen) when the level of an additional substance, called inhibin-A, is also measured.
If you have already done a blood test and/or ultrasound in the first trimester (first trimester screening test), then the results of the two tests together is called an integrated screening test. The results of these tests 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.
An abnormal result does not necessarily mean that your baby has a problem — but it may mean more testing is required. Talk to your health care provider about the risks and advantages of these tests.