Antepartum Testing Health Article

Definition

Antepartum testing involves the use of electronic fetal monitoring (EFM) or ultrasound (US) to assess fetal well-being as determined by the fetal heart rate (FHR) and other characteristics during the antepartal period (ther period spanning conception and labor).

Purpose

Antepartum testing can start as early as 24 weeks but usually after 32 weeks of pregnancy depending on the status of the mother. It provides a means for the physician and pregnant woman to identify fetal well-being and be alert to any changes that may necessitate additional testing or interventions. The results of testing reflect the functioning of the placenta and its ability to adequately supply blood and, therefore, oxygen to the fetus. The testing is done for pregnancies at risk for maternal and/or fetal complications.

Some of these risks include:

• gestational (insulin requiring) diabetes
• intrauterine growth restriction
• chronic hypertension or pregnancy induced hypertension
• too little or too much amniotic fluid (oligohydramnios and polyhydramnios, respectively)
• history of unexplained stillbirth
• autoimmune diseases, including systemic lupus erythematosus
• multiple gestation
• placental abnormalities, i.e. partial abruption (a portion of the placenta pulls away from the wall of the uterus) or placenta previa (the placenta is covering the cervix and subsequent bleeding occurs)

Antepartum testing is used in low-risk pregnancies to evaluate decreased fetal activity, a lag in fundal height (the height of the fundus, measured from pubic symphysis to the highest point in the midline at the top of the uterus), and a postdate pregnancy. A normal pregnancy is 40 weeks and testing should begin at 41 weeks to assess the status of the placenta, which may be no longer capable of meeting the baby's needs. This can be indicated by the FHR pattern, amniotic fluid status, and fetal movement patterns.

Precautions

Clinicians should only prescribe these tests if they are ready to intervene when faced with ominous data. A fetus is considered viable at 24 weeks, as that is the minimum gestational age for sufficient lung development. There are no significant risks to the mother or the fetus from the nonstress test (NST) or the biophysical profile (BPP). Ultrasound waves utilized for the BPP are painless and safe because this method employs no harmful radiation. There is no evidence that sound waves cause any harm to the mother or the baby.

Description

The spectrum of fetal assessment includes fetal movement (FM) counting, nonstress test (NST), contraction stress test (CST), oxytocin contraction stress test (OCT), biophysical profile (BPP), Doppler flow studies, amniocentesis, and cordocentesis. Fetal movement can be determined on a daily basis by the pregnant woman who should be instructed to monitor fetal movement between tests by selecting a consistent time of day and documenting how long it takes to feel 10 fetal movements. She should call her health care provider if there are fewer than 10 movements in 10 hours, or if there are no movements in any 10-hour period. She should also be instructed to report significant decreases in fetal activity from the baby's normal pattern. This daily monitoring of FM by the mother is the least expensive and easiest of all antepartum tests to perform.

The nonstress test (NST) is performed with an electronic fetal monitoring (EFM) that traces the fetal heart rate (FHR) and the presence of any contractions on a monitor. The mother reclines with a slight tilt and the EFM is applied to her abdomen by two straps. The NST indirectly provides information about fetal status by the observation of FHR accelerations with fetal movement. If a fetus is not receiving adequate oxygen from the placenta, the FHR will not accelerate, but if the oxygen supply is sufficient, accelerations will be observed. If it is difficult to obtain fetal movements, a vibroacoustic stimulator (VAS) may be used to provide a loud noise that will awaken the fetus and produce the desired results. The minimum amount of time required for an NST is 20 minutes, but, depending upon the conditions, it may take 60–90 minutes to obtain definitive results.

The contraction stress test (CST) is like the NST except the FHR is evaluated in response to contractions as well as for accelerations. A CST requires the presence of three uterine contractions (UCs) within a 10-minute period lasting at least 40 seconds and of moderate intensity. During a contraction, the blood flow to the baby is temporarily restricted, which provides a form of "stress" to the baby. The baby's response to this stressor reveals significant information regarding the oxygen stores available. If contractions are not present, oxytocin can be given to produce contractions or nipple stimulation may be utilized to produce contractions through the release of natural oxytocin.

The biophysical profile (BPP) is done by an ultrasound exam over a 30-minute period and the examiner looks for fetal movement, fetal tone, breathing movements

(which the mother can perceive as hiccups), and amniotic fluid volume. A score of 0 or 2 points is assigned to each observation with the NST also adding 2 points for a total possible score of 10 points. The modified BPP includes an NST and the determination of the amniotic fluid index by ultrasound, which relates to the amount of fluid present. A physician performs the Doppler flow studies, amniocentesis, and cordocentesis. The majority of health insurance companies do cover a portion, if not all, of the tests' costs.