Diagnosis
Common Prenatal Tests
Initial Prenatal Testing
On your first prenatal visit, it is typical to have your weight, blood pressure, and urine checked and to have a pelvic examination. A blood cell count may be done to determine if their is are any infections, anemia or viruses that might affect the mother’s health or the fetus.
Multiple Marker Test
Between the 15th and 20th weeks of pregnancy, expectant mothers usually are offered a blood test called the multiple marker test. A sample of blood is drawn for measure the levels of:
- HCG – Human Chorionic Gonadotrophin, which is made by the placenta
- estriol – made by the placenta and fetus
- alpha-fetoprotein – made by the fetus
- inhibin-A – made by the placenta
The result of these tests may reveal the need for further testing, such as a more in-depth ultrasound to check for physical abnormalities or an amniocentesis to rule out a genetic disorder.
Ultrasonography
This is a procedure that is harmless to both the fetus and the mother. Sound waves are used to produce visible images of the baby and surrounding fluid. The embryo can first be visualized at about 6 weeks after conception. Major internal organs, arms and legs can be seen at 16 to 20 weeks of gestation to determine if everything is developing normally. The ultrasound can help to determine the size of the fetus, general physical development, where the placenta is, how much fluid surrounds the fetus, but may not be able to detect some abnormalities that are subtle.
Amniocentesis
During this procedure a needle is passed through the mother’s lower abdomen into the amniotic cavity inside the uterus. Enough amniotic fluid is present for this to be accomplished starting about 14 weeks gestation. Most amniocenteses are performed between 14 and 20 weeks gestation. An ultrasound should always proceed amniocentesis in order to determine the age of the fetus, the position of the fetus and placenta, and determine if enough amniotic fluid is present. Fluid is withdrawn with the needle and fetal cells from the fluid are used for testing.
In the third trimester of pregnancy, the amniotic fluid can be analyzed to determine if the fetus has developed fully. This is important when the fetus is younger than 35 to 36 weeks gestation, because the lungs may not be mature enough to sustain life.