What are Prenatal Tests?

For women living in a developed country, with access to medical care, pregnancy most likely means undergoing significant prenatal testing. Prenatal tests are meant to determine if a mother is healthy and free from diseases or disorders that may affect her or the baby during pregnancy, and that the baby is developing normally. There are two basic types of prenatal tests: screening and diagnostic. Screening tests rule out conditions or detect the possible presence of a problem. A diagnostic test is performed to provide a more definite diagnosis of a possible disease or defect.

Prenatal tests can determine a lot about a mother, baby and pregnancy. They can determine a baby’s gender, size, gestational age and location in the uterus. Prenatal tests may also check for genetic, congenital and chromosomal complications, as well as abnormalities in development. There are an estimated 250 different types of birth defects that a baby can develop, most of which are rare or curable.

Prenatal testing is also for the mother’s benefit. Her health affects how the baby will grow and develop, and also determines the pregnancy’s risk to her own life. Tests will identify her blood type, whether she has any conditions such as gestational diabetes, what immunities she carries in her blood and whether she has a potentially dangerous sexually transmitted disease (STD) or cervical cancer.

Prenatal tests will be performed to identify dominant gene disorders like Huntington’s disease, recessive gene disorders such as sickle cell anemia or X-linked disorders such as hemophilia. Other tests can diagnose the presence of Down syndrome resulting from chromosomal disorders, or of disorders caused by environment and genetics, such as spina bifida and anencephaly.

Of course, not all pregnant women undergo all prenatal tests. A doctor will recommend voluntary testing depending on medical history, family medical history, ethnic background, age, previous pregnancies and current state of health. There are many things to consider when deciding on which prenatal tests to consent to. Parents must consider what the tests are looking for, their accuracy, the potential risk to the pregnancy and treatment options. Many mothers who are candidates for certain prenatal tests opt out due to the risk to the baby. Others decide, for whatever reason, that they would not abort a child with a defect.

Blood tests are the foundation of many prenatal tests. With them, the doctor can determine a mother’s blood type, whether she is anemic and if she carries immunity to rubella and chickenpox. Most blood testing is done fairly early in the pregnancy, but it may be continued throughout. Glucose screening, which is conducted from the 24th to 28th week, involves drinking a sugary beverage and having blood drawn to measure blood sugar. This test screens for possible gestational diabetes.

Another blood test, called the Triple Screen, is performed around 16 to 18 weeks and screens the blood for alphafetoprotein (AFP). Doctors use this test to screen for Down syndrome, and it can also calculate the risk of the fetus developing a birth defect.

A cervical exam is usually conducted on the first or second visit during prenatal care. The doctor does a Pap smear to check for cancer and other STDs that can affect the baby during pregnancy and delivery. At about the 35th to 37th week of pregnancy, a swab of the vagina will be taken to test for Group B streptococcus (GBS). Urine tests are performed throughout the pregnancy to monitor protein in the urine. Protein in the urine can signal the development of gestational diabetes and preeclampsia, two very serious complications of pregnancy.

Now a standard of care, the ultrasound test can be performed throughout a high-risk pregnancy, but is usually performed once at 18 to 20 weeks for a normal pregnancy. It checks the baby’s rate of growth, estimates delivery date, monitors heartbeat and breathing, detects abnormalities and checks the amniotic fluid and position of placenta. If you’re lucky, the ultrasound tech may be able to determine the gender of the baby. One of the most notorious prenatal tests, the amniocentesis, is performed at 16 to 18 weeks to diagnose Down syndrome and other chromosomal abnormalities. This test involves inserting a needle into the uterus to collect amniotic fluid.

Other prenatal tests monitor how well the baby is responding to stimuli or contractions of the uterus. No matter what tests you decide to have or forgo, it’s always best to receive prenatal care for the duration of the pregnancy.