Doppler Velocitometry

Real-time ultrasonography machines equipped with Doppler technology can assess arterial velocity and flow. Fetal Doppler studies were initially used to evaluate the placenta by measuring umbilical artery outflow. However, with improved technology, multivessel evaluation became possible. Subsequently, this antenatal test has been the subject of more RCTs than any other antenatal test. The current position of the American College of Obstetricians and Gynecologists (ACOG) on umbilical artery velocitometry is that there is no benefit other than in pregnancies with suspected growth restriction. Its use may alert the clinician to the need for an additional study such as a BPP, continuous fetal monitoring, or delivery.

Fetal Movement Counting

Both human and animal studies indicate that a fetus in trouble (having hypoxemia) will reduce its oxygen requirements by reducing its activity. As a result, FMC is a potentially useful tool for monitoring the fetus during the third trimester of pregnancy. FMC is commonly used to monitor high-risk pregnancies, although there is no RCT evidence to support its use.

Studies of women presenting with decreased fetal movement have produced variable results, ranging from no increase in adverse outcomes to a 3.8% perinatal mortality rate in a cohort of 599 low-risk pregnancies. Grant and colleagues (1989) performed the largest RCT (N = 68,000), which demonstrated that the routine use of FMC in low-risk pregnancies did not improve perinatal outcomes. Although the study authors did not find improved outcomes with FMC, they did conclude that maternal perceptions of decreased fetal movement were as good as formally counted and recorded fetal movement.

Indications

The clinician needs to decide when to use FMC.

• All pregnancies as a routine practice: The evidence does not support daily FMC in all pregnancies (Mangesi and Hofmeyr, 2007). It does support being on the alert for overall decreased fetal movement. Patients who report decreased fetal movement should be instructed to contact their clinicians or to report to labor and delivery.

• High-risk pregnancies: RCTs have not been performed to study the use of FMC in these patients. However, it is a common practice to recommend FMC as a secondary method of fetal surveillance in these pregnancies.

Contraindications

• Impaired mental status or significant linguistic or cultural barrier—any barrier preventing adequate communication or the proper use of FMC could cause screening errors or failures.

• Mother unable to sense fetal movements—there are cases where the clinician can actually see the fetus moving (e.g., during a routine visit, while measuring the fundal height, or otherwise observing the anterior abdomen), yet the patient cannot sense the movement. It may not be possible to use FMC with these patients.

1 The patient should be instructed in the count-to-ten method of FMC (see patient education handout online at www.expertconsult.com). The “Cardiff” count-to-ten method has been studied and compared with the Sadovsky method (three 30- to 60-minute counts at preset times each day) and the Rayburn method (FMC for 60 minutes, once a day). There is a higher patient compliance rate with the count-to-ten method. Instruct the patient to count 10 fetal movements (e.g., swishes, rolls, kicks). The test is complete and considered to be “reassuring” when 10 movements are counted in less than 2 hours. Tests are usually performed in the evening and are often completed within 20 minutes.

2 The patient is instructed to report to labor and delivery or to notify her clinician if 10 movements are not recorded within a 2-hour period. Such a result is a “nonreassuring” screening test.

Complications

Unfortunately, FMC produces frequent false-positive results. A nonreassuring FMC may be further complicated by false-positive follow-up antenatal testing results. These abnormal findings often result in the decision to induce labor, thereby unnecessarily exposing the mother and child to the risks of induction.

Interpretation of Results

A reassuring test is described in the earlier section on Technique. Patients arriving at labor and delivery with a complaint of decreased fetal movement usually undergo an NST. A normal or reactive NST is sufficient to assess fetal well-being. If the NST is not reassuring, then additional antenatal fetal testing will be necessary, such as a BPP or a CST.

Nonstress Test

The NST was introduced in the United States in the early 1970s. Despite the lack of RCT evidence to support its use, the NST is the workhorse of antenatal fetal surveillance. It is usually the first-line test to evaluate high-risk pregnancies and fetal well-being. The NST uses fetal monitoring to document fetal heart rate accelerations that occur in conjunction with fetal movements. Extensive clinical observations have shown a strong correlation between absent or less frequent fetal heart rate accelerations and progressive fetal hypoxia. Conversely, the presence of fetal heart rate accelerations associated with fetal movement (reactive NST) is a reassuring indicator of good fetal health. Although this is not a complex procedure, the clinician must be adept at the proper interpretation of the NST. Important considerations include the indication for testing, gestational age, and any known congenital anomalies or maternal medical conditions. The clinician should also know whether the patient has taken any medications (e.g., narcotics, barbiturates) that might affect the reactivity of the fetal tracing.

Indications

The NST is used to monitor high-risk pregnancies as early as 32 weeks’ gestation. Some of these high-risk conditions include the following:

• Suspected or confirmed intrauterine growth restriction (IUGR; may also use umbilical artery Doppler velocitometry)

• Maternal or gestational diabetes

• Hypertensive disorders of pregnancy

• Prolonged or post-term pregnancy

• Decreased fetal movement

• Maternal trauma

• Other maternal or fetal condition posing risk to the fetus (e.g., renal disease, multiple gestation, substance abuse, prior fetal demise, trauma)

Some clinicians use the NST as early as 26 weeks’ gestation. Different criteria are used to define a reactive or reassuring fetal heart rate tracing before 32 weeks (see Interpretation of Results section). As experience has evolved with the NST, the interval between testing has shortened. Originally set rather arbitrarily at 7 days, more frequent testing is advocated for women with prolonged or post-term pregnancy, type 1 diabetes mellitus, IUGR, or gestational hypertension. In these circumstances, many experts perform twice-weekly NSTs, with more frequent testing for maternal or fetal deterioration. Some even perform NSTs daily, or more frequently, especially for severe preeclampsia remote from term.

Contraindications

There are no specific contraindications to performing an NST, although the test should be aborted if the mother goes into labor and there is marked fetal intolerance of labor.

Preprocedure Patient Education

Before the NST is performed, the patient should be given a handout outlining the procedure and the steps to follow (see sample patient education handout online at www.expertconsult.com). Many testing centers use standardized protocols in an attempt to minimize confounding environmental variables. These protocols encourage the patient to eat about 2 hours before the NST, to not smoke or take sedative drugs before the test, and to remain sedentary during the hour before testing.