The rate of the oetal heart is subject to considerable variations, which aords us a airy reliable means of judging as to the well-being of the child. As a general rule, its lie should be considered in danger when the heart-beats all below 100 or exceed 160.
-J. Whitridge Williams (1903)
More than 100 years ago, the approach to fetal assessment was rather primitive. Since that time, and especially since the 1970s, technology to evaluate the health of the fetus has advanced remarkably. Techniques employed today to forecast fetal wellbeing focus on fetal biophysical indings that include heart rate, movement, breathing, and amnionic luid production. These indings aid antepartum fetal surveillance to prevent fetal death and avoid unnecessary interventions, which are stated goals of the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics (2017).
Most fetuses will be healthy, and usually a negativethat is, normal-antepartum test result is highly reassuring, because fetal deaths within 1 week of a normal test are rare. Indeed, negative-predictive values-a true negative test-for most of the tests described are 99.8 percent or higher. In contrast, estimates of the positive-predictive values-a true positive test-for abnormal test results are low and range between 10 and 40 percent. Importantly, fetal surveillance is primarily based on circumstantial evidence. No deinitive randomized clinical trials have been conducted for obvious ethical reasons (American College of Obstetricians and Gynecologists, 2016).
commences as early as 7 weeks' gestation and becomes more sophisticated and coordinated by the end of pregnancy (Sajapala, 2017; Vindla, 1995). Indeed, beyond 8 menstrual weeks, fetal body movements are never absent for periods exceeding 13 minutes (DeVries, 1985). Between 20 and 30 weeks' gestation, general body movements become organized, and the fetus starts to show rest-activity cycles (Sorokin, 1982). Fetal movement maturation continues until approximately 36 weeks, when behavioral states are established in most normal fetuses. Nijhuis and colleagues (1982) described four fetal behavioral states:
State 1 F 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 (EM) or active sleep in the neonate.
State 3F includes continuous eye movements in the absence ofbody movements and no heart rate accelerations. he existence of this state is disputed (Pillai, 1990a).
State 4F is one ofvigorous body movement with continuous eye movements and heart rate accelerations. his state corresponds to the awake state in newborns.
Fetuses spend most of their time in states IF and 2F. For example, at 38 weeks, 75 percent of time is spent in these two states. hese behavioral states-particularly IF and 2F, which correspond to quiet sleep and active sleep-have been used to develop an increasingly sophisticated understanding offetal behavior. In a study offetal urine production, bladder volumes increased during state IF quiet sleep (Fig. 17-1). Duringstate 2F, the fetal heart rate baseline bandwidth increased appreciably, and bladder volume was signiicantly diminished due to decreased urine production and infrequent fetal voiding. These phenomena were interpreted to represent reduced renal blood flow during active sleep.