The big-deal tests

Here's the 411 on the five main (and optional) screening and diagnostic tools. For more details, check out the Pregnancy Planner on Babytalk.com

test: Ultrasound
At any point in your pregnancy your care provider can perform this very safe test, which uses sound waves to make a picture of your baby on a screen. This test can reveal the age and sex of your fetus, whether you're having multiples, how much amniotic fluid you have, and if the baby is growing as he should.

test: First-trimester screen
Between 10 and 14 weeks, a special type of ultrasound called nuchal translucency screening is used to measure the thickness on the back of the neck of the fetus. A serum (blood) test is also done, and the combination of results can indicate whether the baby is at risk for a heart defect, Down syndrome, or Trisomy 18 (a chromosomal disorder also called Edward syndrome).

test: Chorionic villus sampling (CVS)
At 10 to 12 weeks, the doctor can insert a thin tube into the uterus, through either the birth canal or a needle in the belly, and take a sample of the tissues of the placenta. This sample can be used to detect Down syndrome, cystic fibrosis, sickle cell anemia, and other disorders. There is a 1 percent chance of miscarriage with this test.

test: Maternal serum screen
Given between 15 and 20 weeks, this blood test (also known as the triple/quad screen), is used to analyze the levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), inhibin, and unconjugated estriol. These substances, along with the mother's age, can be used to estimate the probability of Down syndrome, Trisomy 18, and neural tube defects such as spina bifida and anencephaly (absence of a major part of the brain and the top part of the skull).

test: Amniocentesis
At 15 to 20 weeks, a doctor guides a needle through the mother's abdomen and uterus to withdraw amniotic fluid. The test can diagnose numerous abnormalities and illnesses, as well as confirm the gender of your baby. It's typically offered to women over age 35 who have a higher risk of Down syndrome, women who have a family history or another child with certain birth defects, or women whose prior tests indicated a cause for concern. The chance of miscarriage is 1 in 400 to 1 in 200.