Chapter 12: Fetal Health Surveillance in Labor

INDICATIONS FOR FETAL ASSESSMENT

There are numerous situations in which it is important to ascertain both the maturity and the health of the fetus while it is still in utero. Among these are the following:

During Pregnancy

Patients at Risk for Uteroplacental Insufficiency

1. Diabetes mellitus

2. Hypertension and preeclampsia

3. Renal disease

4. Previous stillbirth

5. Intrauterine growth restriction, suspected

6. Postterm pregnancy (over 42 weeks)

7. Isoimmunization

8. Preterm premature rupture of membranes

9. Multiple gestation

10. History of placental abruption

11. Chronic abruption

12. Maternal obesity

13. Abnormal maternal serum screening in the absence of fetal anomaly

14. Oligohydramnios or polyhydramnios

Obstetric Reasons

1. Previous cesarean section

2. When induction of labor is necessary

   1. In the interests of the mother

   2. In the interests of the fetus

During Labor

Obstetric Reasons

1. Clinically detected abnormalities of the fetal heart rate (FHR)

2. Passage of meconium

3. Oxytocin stimulation of labor

4. Preterm labor

5. Slow progress in labor

6. Abnormal presentation

DETERMINATION OF FETAL HEALTH: ANTEPARTUM

In North America, antenatal and intrapartum deaths are rare. The reduction in the perinatal mortality rate has been achieved largely by the decrease in the rate of neonatal death. The prevention of fetal death represents a major therapeutic goal, and is the reason for antepartum fetal surveillance.

Biochemical assessment of the fetus has largely been replaced by biophysical and biometric evaluation. Fetal biophysical activities are initiated, modulated, and regulated by mechanisms of the central nervous system (CNS). A fetus compromised by hypoxia demonstrates one or both of the following changes:

1. A decrease or cessation of biophysical activity

2. A significant reduction in the volume of amniotic fluid that becomes evident as oligohydramnios on sonography

The fetal CNS is exquisitely sensitive to changes in PO₂. Hypoxia and its resultant metabolic acidosis produce pathologic CNS depression with changes in biophysical activity. Any biophysical response, however, has its own inherent periodicity and circadian (diurnal) rhythm. Hence, the absence of a given biophysical event may reflect physiologic periodicity, and a normal “sleep state” in a fetus must be differentiated from the comatose state of hypoxic CNS depression.

The important principle in antepartum testing, regardless of the method used, is that a normal test result is reliable in indicating present fetal well-being and is an accurate predictor of a good outcome. However, the diagnosis of fetal jeopardy, based on a single absent or abnormal biophysical event, is frequently inaccurate. Hence, in any scheme of antepartum testing, the goal must be to reduce and, if possible, eliminate the incidence of falsely positive results. This is achieved by increasing the period of observation for any single biophysical event and/or using multiple observations. The demonstration of several biophysical activities showing a normal pattern collectively negates a single abnormal result.