Antenatal Testing Health Article

Definition

Antenatal testing describes procedures performed during pregnancy to detect health problems in the growing fetus; establish characteristics such as fetal age, sex, or weight; or diagnose any material conditions that may affect fetal development.

Purpose

Antenatal tests and exams are important tools for protecting the health of a pregnant woman and her developing child. Various tests are administered over the course of pregnancy to determine if the mother has any health conditions that may interfere with normal development of the fetus or if the fetus has any health conditions that may affect the baby's quality of life. Often, families will use information provided by the tests to prepare for the baby's birth and make arrangements for special care if needed or make the decision to terminate the pregnancy. Physicians also use antenatal tests to determine various characteristics of the fetus, such as gestational age, size, and position in the uterus, or to verify the presence of multiple fetuses.

Description

Women who become pregnant may undergo tests at any stage in their pregnancy: during the first trimester (weeks one through 12), second trimester (weeks 13–26), or third trimester (weeks 27–40+). What tests are ordered depends on the stage of pregnancy, the age and health of the mother, the medical history of both parents, and the family's background or ethnicity. There are two distinct types of antenatal tests:

• Screening tests tend to be less invasive and indicate the possibility of a certain genetic disorder or birth defect but do not determine with certainty that the abnormality exists.
• Diagnostic tests tend to more invasive but are able to determine with more certainty that a fetus will be born with a certain condition.

Blood and urine tests

In the early stages of pregnancy, physicians may order blood or urine tests to screen for possible disorders or infections that could affect the growing fetus. The tests may also be ordered in later stages if the pregnant woman comes in contact with an infectious agent or develops symptoms of infection. In many cases, complications can be avoided if early diagnosis is made and treatment initiated. Examples of conditions that are commonly screened for with blood and/or urine tests include:

• Rh factor: About 15 percent of people lack a certain blood protein called Rh factor and are called Rh negative. Complications may arise if an Rh-negative mother is carrying an Rh-positive child. These can be avoided if the mother is given a substance called Rh immune globulin (RhIg) at approximately 28 weeks into the pregnancy and again within 72 hours after the baby is born.
• Anemia: If there is too little of a substance called hemoglobin in a pregnant woman's red blood cells, a condition called anemia may result. If a blood test reveals low hemoglobin, supplementation with iron may be recommended.
• Human immunodeficiency virus: HIV can be transmitted from mother to child, although treatment of the disease during pregnancy can greatly reduce the risk of transmission. Because it is possible for individuals to be infected without exhibiting symptoms and because unprotected sex is a major risk factor for contracting the virus, the American Academy of Pediatrics recommended in 1999 that a screening test for HIV be routinely offered. A second test later in pregnancy may be recommended if the pregnant woman is considered to be at high risk of becoming infected with HIV.
• Syphilis: If transmitted from mother to child during pregnancy, syphilis leads to death of the fetus or newborn in approximately 40 percent of cases. The goal of syphilis screening is to diagnose and treat infections before transmission occurs. Syphilis is treated with antibiotics.
• Rubella (German measles): Although the majority of women in the United States are immune to rubella because of prior immunization or infection, serious complications to the fetus (such as deafness, blindness, or heart defects) can arise if a woman becomes infected during pregnancy. If a woman is found to not have immunity, it will be recommended that she avoid contact with infected individuals during her pregnancy and receive a vaccination against rubella after she gives birth.
• Group beta strep (GBS): GBS is a type of bacteria commonly found in the vagina and rectum. GBS can be present in a person's body without causing any symptoms, so many women do not realize they are infected with it. Newborns who are exposed to GBS, however, can develop serious complications such as meningitis, pneumonia, blindness, deafness, and death is possible. Doctors test for the presence of GBS in urine or in samples collected from the vagina or rectum. This test is usually performed late in pregnancy, at 35 to 37 weeks of gestation. If a woman is found to be infected with GBS, physicians generally administer antibiotics to the mother so the baby is not born with the infection.

A multiple marker test or triple screen is used to determine if a fetus is at an increased risk of having certain congenital abnormalities. The test has a high rate of false-positives; as few as 10 percent of women with abnormal results go on to have babies with congenital defects. The purpose of the test is to determine if further testing (such as ultrasound or amniocentesis) is warranted. The test requires a sample of maternal blood, typically taken during the fifteenth and twentieth week of pregnancy, and measures the level of certain pregnancy hormones.