Second Trimester Tests During Pregnancy
Here are the prenatal tests that may be performed in the second trimester of your pregnancy:
Maternal serum alpha-fetoprotein (MSAFP) and multiple marker screening: One or the other is offered routinely in the second trimester. This test is an optional genetic screening test and as with all screening tests, talk with your doctor about the pros and cons to see if it is right for you. The MSAFP test measures the level of alpha-fetoprotein, a protein produced by the fetus. Abnormal levels indicate the possibility (but not existence) of Down syndrome or a neural tube defect such as spina bifida, which can then be confirmed by ultrasound or amniocentesis.
When blood drawn for the MSAFP test is also used to check levels of the hormones estriol and hCG, it's called the triple test. When a marker called inhibin-A is added to the screen, it is known as the quad marker. The quad marker test significantly boosts the detection rates for Down syndrome. The test picks up about 75% of neural tube defects and 75%-90% of Down syndrome cases (depending on the mother's age), but many women will have a false-positive screening. About 3% to 5% of women who have the screening test will have an abnormal reading, but only a small percentage of those women will actually have a child with a genetic problem.
Ultrasounds: Ultrasounds (sonograms) are commonly offered week 20, although they may be done at any time during a pregnancy. A sonogram may be offered for a variety of reasons, including verifying a due date, checking for multiple fetuses, investigating complications such as placenta previa (a low-lying placenta) or slow fetal growth, or detecting malformations like cleft palate. Sometimes, if there are findings suspicious for a genetic abnormality seen, you may be referred to a specialist or for further genetic testing. During the procedure, a device is moved across the abdomen that transmits sound waves to create an image of the uterus and fetus on a computer monitor. New three-dimensional sonograms provide an even clearer picture of your baby, but they aren't available everywhere and it's not clear whether they're any better than two-dimensional pictures in contributing to a healthy pregnancy or birth.