Techniques employed to evaluate fetal health focus on fetal biophysical findings that include heart rate, movement, breathing, and amnionic fluid production. Antepartum fetal surveillance aims to prevent fetal death in pregnancies with complex maternal and fetal conditions yet avoid unnecessary interventions (American College of Obstetricians and Gynecologists, 2021a).
Most fetuses will be healthy, and a normal antepartum test result is highly reassuring. Fetal death within 1 week of a normal test result is rare. Indeed, negative predictive values—true negative test results for fetal jeopardy—for most of the tests described are 99.8 percent or higher. In contrast, estimates of positive predictive values—true positive test results for fetal jeopardy—are low and range between 10 and 40 percent. The benefit of fetal surveillance is primarily based on circumstantial evidence. No definitive randomized clinical trials have been conducted for obvious ethical reasons (American College of Obstetricians and Gynecologists, 2021a).
Fetal activity commences as early as 7 weeks’ gestation (Sajapala, 2017; Vindla, 1995). Between 20 and 30 weeks’ gestation, general body movements become organized, and the fetus starts to show rest-activity cycles (Sorokin, 1982). These cycles reflect central nervous system development and maturation. By approximately 36 weeks’ gestation, rest-activity cycles give way to behavioral states in most normal fetuses (Peirano, 2003). Four fetal behavioral states are described by Nijhuis and coworkers (1982):
State 1F is a quiescent state—quiet sleep—with a narrow oscillatory bandwidth of the fetal heart rate.
State 2F includes frequent gross body movements, continuous eye movements, and wider oscillation of the fetal heart rate. This state is analogous to rapid eye movement (REM) or active sleep in the neonate.
State 3F includes continuous eye movements in the absence of body movements and no heart rate accelerations. This state is rare, and its existence is disputed (Pillai, 1990a).
State 4F is one of vigorous body movement with continuous eye movements and heart rate accelerations. This state corresponds to the awake state in newborns.
At 28 to 30 weeks’ gestation, fetuses transition to spend most of their time in states 1F and 2F, namely, in quiet or active sleep (Fig. 20-1) (Peirano 2003; Suwanrath, 2010). For example, at 38 weeks, 75 percent of time is spent in these two states. These behavioral states have been used to develop an increasingly sophisticated understanding of fetal behavior. In a study of fetal urine production, bladder volumes rose during state 1F quiet sleep and significantly declined during state 2F active sleep due to diminished urine production and infrequent fetal voiding (Oosterhof, 1993). These phenomena were thought to represent reduced renal blood flow during active sleep.
The change in fetal sleep patterns (blue columns) and corresponding number of accelerations (graph lines). As the ...