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Week 16

Your Baby's Development

Watch Your Baby Grow

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 their head up, and the development of facial muscles allows for a variety of expressions, such as squinting and frowning.

Week 16

Your Body

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). This test measures:

  • the levels of alpha-fetoprotein (AFP), a protein made by the fetus
  • the pregnancy hormones hCG and estriol in the mother's blood

Sometimes, the level of another substance, inhibin-A, is also measured. Then, the test is called a quadruple screen (or quad screen).

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 if 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 a baby has a problem. But it may mean more testing is needed. Talk to your health care provider about the risks and advantages of these tests.

PREGNANCY CALENDAR: A week-by-week guide