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Antepartum Fetal Surveillance

Common Indications for Testing

Diabetes

Decreased fetal movement

Hypertension

Isoimmunization

IUGR

Maternal cyanotic heart disease

Maternal renal disease

Oligohydramnios

Postterm pregnancy

PROM

Sickle cell disease

Systemic lupus erythematosus

Testing is usually begun when the diagnosis is established, usually in the third trimester. For long-standing fetal conditions or chronic maternal medical complications, the timing depends on the severity of the condition. Usually testing begins at 32-34 weeks of gestation, although it may be warranted as early as 26-28 weeks of gestation with conditions such as diabetes, chronic hypertension, and isoimmunization.

Techniques

There is considerable controversy regarding which test of antepartum fetal health is most appropriate antepartum surveillance, fetal surveillance, surveillance, fetal monitoring. The nonstress test (NST) is the easiest test to use but has a high false-positive rate. Late decelerations occur earlier than do the loss of beat-to-beat variability and accelerations as indicated on an otherwise-normal heart rate tracing. Specifically, the loss of baseline variability usually occurs after fetal hypoxia has been severe enough to produce acidosis. Consequently, the contraction stress test (CST) is probably an earlier and more sensitive indicator of fetal hypoxia than the NST. In large clinical studies, however, both tests appear to be reasonably accurate

NONSTRESS TEST

The NST is generally accepted as the simplest screening test for fetal compromise in the antepartum period. It is best to carry out this test with the patient either in the slightly tilted, recumbent position or in the semi-Fowler position to minimize compression of the maternal vena cava by the uterus. The fetal heart rate (FHR) is recorded by using an external Doppler ultrasound device. An external tocodynamometer is used as well.

The protocol for the NST generally involves recording the FHR for 20-40 minutes, with the patient pressing a marker button when there is fetal movement. There are various criteria for the number of accelerations required during a certain period, as well as for the amplitude and duration of the accelerations. It is generally

BIOPHYSICAL PROFILE

The BPP combines the NST with fetal ultrasound parameters. In a 30-minute period, the fetus should exhibit movement, breathing motions, and evidence of tone as described in Table 2. In addition, the amniotic fluid volume is assessed and the NST results are recorded.

The total score obtained reflects the fetal status. A score of 8-10 is normal and correlates highly with normal fetal umbilical cord blood gases and a normal fetal outcome. A score of 6 is considered equivocal and

CONTRACTION STRESS TEST

The CST attempts to mimic labor by inducing mild uterine contractions. Contractions may be spontaneous or may be generated either by oxytocin or by nipple stimulation. The heart rate is monitored continuously and compared with the contraction pattern. The presence of late decelerations suggests that the fetus has

FETAL MOVEMENT

The antepartum use of fetal movement counting (or kick counts) may decrease antepartum stillbirth rates in low-risk women. In the fetal movement test, the pregnant woman records the length of time that the

FETAL UMBILICAL ARTERY VELOCIMETRY

Recently, Doppler fetal umbilical artery velocimetry has been used to measure increased placental vascular resistance, which may potentially allow for the recognition of placental dysfunction. However, due to its low positive predictive value, Doppler ultrasonography is not a screening test for detecting fetal compromise in