Intrauterine and Intrapartum Assessment of the Fetus

Maturational Changes

Distinct maturational changes in fetal movement can be identified ( Fig. 21.1 ). Although with ultrasonography it is possible to detect movement as early as the second month of gestation, maternal perception of movement (“quickening”) occurs at approximately 16 weeks. Thereafter, the movements increase in strength and reach a plateau from 26 to 32 weeks of gestation, when an abrupt fall to a second plateau occurs between 32 and 36 weeks. No appreciable change occurs thereafter until delivery. A recent cross-sectional study examining maternal perception of fetal movement in pregnancies with normal outcome found that the strength of fetal movements in the last trimester is accretive, with frequent presence of fetal hiccup, and that a diurnal pattern of fetal movements is much more commonly appreciated in the evening and at nighttime, including bedtime. These investigators emphasized that a more sensitive marker of fetal well-being is a change in the quality of fetal movements compared with arithmetic counting.

Prechtl and others emphasized the quality of fetal movements and the striking maturational changes in the variety and complexity of these movements. Certain fetal movements increase in incidence gradually with advancing gestation (e.g., breathing, sucking, and swallowing); other movements increase in incidence to a plateau (e.g., general movements, isolated arm movements); and still others increase in incidence and then decrease (e.g., startles, hiccups).

Relation of Fetal Movement to Fetal Well-Being

The relation of quantity and quality of fetal movement to fetal well-being is illustrated by the study summarized in Fig. 21.2 . Most investigations examining fetal movements and perinatal outcomes have done so through two fundamentally different but related ways . The first series of studies has examined the association of altered fetal movements in retrospective case-control studies of women who experienced a stillbirth infant compared with controls. The second series of studies have prospectively studied the effect of maternal monitoring of fetal movements on perinatal outcomes, focused on reduction in stillbirths.

Concerning the retrospective association of reduced fetal movements with women who experienced stillbirth, it has been estimated approximately 30% to 55% of women who have a late stillbirth will have experienced an episode of reduced fetal movement within a week of their stillbirth. With specific regard to the observation that reduced fetal movements are a risk indicator for stillbirth, there have been six large cohort case-control studies published since 2015 that have assessed the relationship between women’s reporting reduced fetal movements and stillbirth, with all of them documenting a positive correlation between reduced fetal movements and stillbirth ( Table 21.3 ).

With more specific regard to the nature of the fetal movements, in one large study it was noted that not only decreased frequency of fetal movements (adjusted odds ratio [aOR] 2.29, 95% confidence interval [CI] 1.31 to 4.0) but also the perception of “quiet or light” fetal movement in the evening (aOR 3.82, 95% CI 1.57 to 9.31) was associated with an increased risk for late stillbirth. Conversely, the investigators also noted that more instances of “more vigorous than usual” fetal movement (aOR 0.52, 95% CI 0.32 to 0.82), daily perception of fetal hiccups (aOR 0.28, 95% CI 0.15 to 0.52), and increased length of fetal movement clusters or “busy times” (aOR 0.23, 95% CI 0.11 to 0.47) were all associated with reduced risk of stillbirth. In conclusion, in these retrospective studies women with stillbirth were more likely than controls to have experienced alterations in fetal movement, including decreased strength, frequency, and in particular a fetus that was “quiet” in the evening .

However, although this association is reported retrospectively by women who have experienced a stillbirth, the effect of the prospective maternal monitoring for reduced fetal movements on perinatal outcomes has been of less clear association with stillbirth ( Table 21.3 ). Two recent large studies examined the effect of training interventions to increase women’s awareness of fetal movements to reduce the incidence of stillbirths and other adverse perinatal outcomes. Both studies found that increasing women’s awareness toward fetal movements was not associated with reduced stillbirth incidence or improved perinatal outcome. The AFFIRM study was the larger of these studies and included 33 hospitals with data collected from 409,175 pregnancies (157,692 deliveries during the control period, 23,623 deliveries in the washout period, and 227,860 deliveries in the intervention period). The incidence of stillbirth was 4.40 per 1000 births during the control period and 4.06 per 1000 births in the intervention period (aOR 0.90, 95% CI 0.75 to 1.07; P = .23). The authors concluded that the reduced fetal movements care package did not lead to a reduction in the risk of stillbirths and that the benefits of a policy that promotes awareness of reduced fetal movements remain unproven.

These findings are consistent with a Cochrane review from 2015 on the efficacy of fetal movement counting for the assessment of fetal well-being, which included five studies with 71,458 women. All included women with uncomplicated pregnancies, except one study that included high-risk women as participants. Two studies compared fetal movement counting with standard care, as defined by trial author. Two studies compared two types of fetal movement counting comparing once-a-day (Cardiff Count to Ten) with more than once-a-day fetal movement counting methods. One study compared fetal movement counting with hormone assessment evaluated with an average of five determinations of serum total estriol and human placental lactogen. The first comparison of fetal movement monitoring compared with standard care showed no difference in mean stillbirth rates (standard mean difference 0.23, 95% CI 0.61 to 1.07) or fetal deaths. There was no difference in cesarean section rate between groups within any of these three comparisons of fetal movement monitoring. There were no data on perinatal mortality or severe morbidities. The conclusions of the Cochrane review were that sufficient evidence did not exist to influence clinical practice.

In a more recent systematic review, women who used fetal movement counting once or more per week had fewer stillbirths by 21% than did control women, a difference with a strong trend that was not statistically significant. However, in the studies that included women who undertook systematic counting of fetal movements ( n = 11,069), a significant reduction in the rate of stillbirth was found.

Despite the evidence demonstrating a strong association between reduced fetal movements and stillbirth, the majority of women reporting reduced fetal movements will have a healthy baby. Approximately 10% to 15% of women of late pregnancy will experience symptoms of reduced fetal movements but the percentage of fetal death is much lower than 10% to 15%.

It remains a common obstetrical practice to educate women about the normal range and duration of fetal movements to count 10 fetal movements typically within 30 minutes ( Table 21.3 ). Others have suggested that rather than the counting-to-10 alarm limits, every woman should be familiarized with her own baby’s characteristics of movements to detect deviations in the personal pattern. Currently, the World Health Organization continues to recommend the daily surveillance of fetal movements, using any kind of method, as an effort to make pregnant women and health care professionals aware of the importance of fetal movements as an indicator of fetal well-being, especially in late pregnancy.

Fetal Neurological Examination

The observations described in the preceding paragraphs are reminiscent of many of those made during the neonatal neurological examination. The use of fetal movements as part of a detailed analysis of fetal behavior by real-time ultrasonography led to the identification of distinct behavioral states , as noted earlier. These analyses include assessment of a large variety of specific body movements (e.g., yawning, stretching, and startle), as well as fetal eye movements, posture, breathing, and heart rate. The analogy of these phenomena to those observed after birth in the premature infant (see Chapter 12 ) is obvious, and, indeed, to a major extent, one can consider these observations a kind of fetal neurological examination . When amplified by such assessments as habituation of the fetus to vibrotactile stimuli or response to acoustical stimuli, the analogy to neurological assessment becomes even more impressive. Finally, detailed analysis of the quantity and quality of fetal breathing can provide still further information about the fetal nervous system. A recent review noted the major factors that can affect the behaviors of fetal body movements, breathing, and fetal behavioral states ( Table 21.4 ). With the wide use of real-time ultrasonography, the standardization of the neurological phenomena observable, and—most important and still most difficult—the correlation of aberrations with the topography of neuropathology, highly valuable evaluation of the fetal central nervous system (CNS) and dysfunction thereof should be possible. The design of appropriate interventions for disturbances then would be an appropriate next step.

Nonstress Test

Of the two techniques, the nonstress test is the approach often used as an initial evaluation. In general, the particular value of the technique is the determination of a healthy fetus, based on the demonstration of at least two accelerations of FHR during the period of observation (usually ≈40 minutes), generally in association with fetal movement or vibroacoustical stimulation. The accelerations must exceed 15 beats/min and last at least 15 seconds, and the normal result is called a reactive nonstress test. A nonreactive test is characterized by the failure to note such accelerations over the observation period. The demonstration of accelerations of FHR with acoustical stimulation and the correlation of a reactive acoustical stimulation test with the conventional nonstress test have led to use of such stimulation as part of the nonstress test in many centers.

Concerning the predictive value of nonstress testing, the incidence of fetal distress leading to cesarean delivery increases from about 1% to 20% when antepartum reactive and nonreactive patterns are compared. It is clear, however, that most “abnormal” or nonreactive tests are not followed by difficulties with labor and delivery. A normal, reactive nonstress test is highly predictive of fetal well-being. Thus, as with most other modes of fetal evaluation, both antepartum and intrapartum, the prediction of a normal fetus and the relative lack of need for intervention are the greatest values of the test .

Nonstress tests appear to have less value in noncompromised fetuses before 32 weeks of gestation. Between 24 and 28 weeks gestational age, up to 50% of nonstress tests have been documented as nonreactive, decreasing to 15% being nonreactive from 28 to 32 weeks. In general, 15% of all nonstress tests will be nonreactive. In the largest series of nonstress tests, the stillbirth rate (corrected) was 1.9 per 1000. Thus, the negative predictive value is 99.8%, with a high false-positive rate (75% to 90%) associated with nonreactive nonstress tests. In addition, the test does not detect such important maternal-fetal problems as oligohydramnios, umbilical cord or placental abnormalities, growth disorders, and twin demise. When suspicion or concern for such problems exists, another approach, using ultrasonography, as in fetal biophysical profile, is essential. Despite the rational approach to these measures of fetal behavior and well-being, several randomized prospective trials that have used weekly surveillance with nonstress tests have shown no benefit to the fetus or infant.

Contraction Stress Test

The contraction stress test in the past was most commonly used as a follow-up evaluation after a nonreactive stress test. Experimental data suggest that the occurrence of late decelerations with contractions, the basis for a positive (abnormal) stress test , is an early warning sign of uteroplacental insufficiency. The established clinical and experimental premise of the stress test is that chronic uteroplacental insufficiency results in late decelerations of the FHR, a sign of fetal hypoxia (see following discussion), in response to uterine contractions, which can be stimulated by breast stimulation or oxytocin infusion. In approximately 10% of women, spontaneous uterine contractions obviate the need to stimulate uterine contractions. A positive (abnormal) result is indicated by persistent late decelerations over several or more contractions; these positive tests can be subdivided further as reactive , when accompanied by accelerations at some time during the test, or nonreactive , when not accompanied by accelerations. An equivocal result refers to the occurrence of nonpersistent late decelerations . A negative stress test is defined as absence of any late decelerations with the contractions.

As with nonstress testing and other fetal assessments, a negative stress test is a reliable indicator of fetal well-being. Concerning the predictive value of a positive stress test, in one multiinstitutional study of high-risk pregnancies, a negative test was followed by perinatal death in less than 1% of cases versus 5% to 20% of infants with positive contraction tests (the lower value was for infants with reactive positive tests, and the higher value was for those with nonreactive positive tests). Similarly, an Australian study showed that among 72 patients with nonreactive positive spontaneous contraction stress test results, there was a 28% perinatal mortality rate and of the 42 infants that survived the neonatal period and were assessed, 27% had neurological handicap.

Currently, the contraction stress test is no longer the principal method for follow-up in most centers. This change relates to logistical and interpretive difficulties and relatively low positive predictive values. The fetal biophysical profile is now favored as the primary means of fetal surveillance for high-risk pregnancies, identified by a nonreactive nonstress test or other evidence.

Umbilical Artery

Most studies based on the use of Doppler in pregnancy have focused on the UA. The principal quantitative parameters of the Doppler waveform used have been the PI of Gosling (peak systolic velocity [PSV] – end diastolic velocity [EDV]/mean velocity), the resistance index of Pourcelot (PSV-EDV/PSV) and the PSV/EDV ratio . The values of these ratios, in general, are not affected by the angle of insonation, clearly difficult to maintain constant in the clinical situation. The PI and the resistance index reflect, in largest part, vascular resistance. The principal change in UA blood flow velocity with progression of normal pregnancy is a decline in the resistance parameters. Although the decline is gradual, a more pronounced decrease occurs after 30 weeks of gestation. This decrease is considered secondary to a decrease in placental vascular resistance, related particularly to increased numbers of small vessels. A similar phenomenon was documented in the fetal lamb. The decrease in placental vascular resistance with advancing pregnancy is accompanied by an increase in volemic placental blood flow, calculated in human fetuses by simultaneous measurements of the blood flow velocity in the umbilical vein and the cross-sectional area of that vessel by combined Doppler and imaging ultrasonography ( Fig. 21.6 ).

The major application of Doppler studies of blood flow velocity in the UA has been in the investigation of the high-risk fetus. In intrauterine growth retardation, the principal finding is an increase in the resistance measures. With progression of this disturbance in resistance measures in the UA, marked impairment of the end diastolic flow (EDF) or even loss or reversal of diastolic flow (an ominous sign) may occur ( Fig. 21.7 ).

In one study, the changes in resistance indices preceded antepartum late heart rate decelerations in more than 90% of fetuses who developed such decelerations, and the median duration of the interval between the severe abnormality of resistance measure and decelerations was 17 days. The importance of the rising placental vascular resistance to the fetus is shown by the striking curvilinear relationship between the PI in the UA and the lactate concentration in fetal blood, a measure of fetal hypoxia ( Fig. 21.8 ). The clinical predictive value of the diastolic flow in the UA was apparent in a study of 459 high-risk pregnancies. Thus, the rate of fetal or neonatal death in the presence of EDF was 4% and increased to 41% with absence of flow and to 75% with reversal of flow. With prompt and detailed further fetal assessments and appropriate interventions, the unfavorable outlook with absence of diastolic flow has not been so marked. However, reversal of flow is associated with a considerable risk of fetal compromise, perinatal mortality, neonatal neurological disturbances, and subsequent neurodevelopmental disability, with the magnitude of risk varying considerably with the selection of the population studied.

The use of Doppler assessment of the UA flow in fetuses with growth restriction or those at risk, such as hypertensive pregnancies, has been shown to lead to a reduction in perinatal mortality and reduced unnecessary obstetrical intervention. Further meta-analyses, comparing the use of umbilical Doppler in high-risk groups, has confirmed this conclusion. A recent Cochrane review with 18 studies and more than 10,000 pregnancies, demonstrated that women with Doppler assessment had a significantly lower perinatal mortality (1.2%) compared with those without Doppler studies (1.7%) (risk ratio [RR] 0.67, 95% CI 0.46 to 0.96). Although the data for secondary outcomes showed that there were fewer adverse outcomes in the Doppler group, this finding did not reach statistical significance. Interestingly, there was a reduction in interventions, such as induction of labor and cesarean delivery in the Doppler group. Importantly, though, there is a lack of data on long-term neurological development on the infants in either group.

The central abnormality in the growth-retarded fetus leading to the increase in placental vascular resistance is a disturbance in placental vessels. The major features include loss of small blood vessels, decreased vascular diameter because of media and intima thickening, and thrombosis. Placental vascular obstruction produced by a variety of experimental techniques in pregnant sheep reproduced the changes in the resistance measures observed in the human fetus. Indeed, elevated UA resistance measures have been observed in a variety of pathological conditions of the placenta, including partial abruption, placental scarring from intervillous thrombosis, and inflammatory villitis secondary to bacterial or viral infection. Thus, the value of this technique in the evaluation of a wide variety of high-risk pregnancies is very high.

The most recent Cochrane review of fetal and umbilical Doppler ultrasound in high-risk pregnancies found that the use of Doppler ultrasound of the UA was associated with fewer perinatal deaths (RR 0.71, 95% CI 0.52 to 0.98; 16 studies, 10,225 babies, 1.2% vs. 1.7%). The results for stillbirths were consistent with the overall rate of perinatal deaths, although there was no difference between groups for this outcome (RR 0.65, 95% CI 0.41 to 1.04; 15 studies, 9560 babies). When Doppler ultrasound was used, there were fewer inductions of labor (average RR 0.89, 95% CI 0.80 to 0.99; 10 studies, 5633 women) and fewer cesarean sections (RR 0.90, 95section Rsection 0.90section 95% CI 0.84 to 0.97; 14 studies, 7918 women). No difference was found in operative vaginal births (RR 0.95, 95% CI 0.80 to 1.14; four studies, 2813 women), or in Apgar scores lower than 7 at 5 minutes (RR 0.92, 95% CI 0.69 to 1.24, seven studies, 6321 babies). Data for serious neonatal morbidity were not pooled because of high heterogeneity between the three studies that reported this outcome (1098 babies).

In a recent review of the international guidelines for the surveillance and timing of birth in infants with IUGR, Doppler evaluations of the UA were considered a key mode of surveillance and mode for determination of the timing and mode of delivery ( Table 21.7 ).

In contrast, Doppler measurement of UA flow has been shown repeatedly not to be useful in a low-risk or unselected population . A Cochrane review, including more than 14,000 women from 20 studies, compared the outcomes of low-risk pregnancies with either routine ultrasound or no Doppler ultrasound. This comparison failed to demonstrate a reduction in perinatal death or serious neonatal morbidity in the Doppler group, nor were there differences in the secondary outcomes, including prematurity, mode of delivery, neonatal resuscitation, or a 5-minute Apgar score lower than 7.

Fetal Cerebral Vessels

Fetal MCA Doppler has been proposed as an additional test to UA Doppler. The changes in the fetal MCA may better reflect fetal cardiovascular adaptations to hypoxia or blood flow redistribution that may have neurological effects. There are multiple measures from the fetal MCA, including EDV, PSV, and time-averaged (mean) velocity (TAV). The fetal MCA PI has become a key parameter used in fetal middle cerebral arterial Doppler assessment being calculated by subtracting the EDV from the PSV and then dividing by the TAV. A decrease in the PI has been considered a compensatory phenomenon to protect the fetal brain in the context of IUGR. During normal pregnancy , in contrast to the decreasing values for resistance measures defined in the umbilical circulation, values in the cerebral circulation change little until approximately the last 5 weeks, when a distinct decline is apparent ( Fig. 21.9 ).

As with Doppler studies of the umbilical vessels, study of cerebral blood flow velocity has been directed most commonly at the growth-retarded fetus. The dominant abnormality has been a diminished value of cerebral resistance indices, in contrast to the elevated value in the UA ( Fig. 21.10 ). This apparent vasodilation in the cerebrum at a time of decreasing umbilical flow has been interpreted as an adaptive response, perhaps mediated by hypoxia, and has been termed fetal brain sparing . It seems reasonable to suggest that, with severe impairment of umbilical flow and hypoxia, such an adaptive response could become insufficient. Indeed, the decline in cerebral resistance indices and the increase in umbilical resistance indices have been quantitatively combined as a cerebral-to-umbilical ratio.

An adaptation of MCA Doppler study is the cerebroplacental ratio (CPR), which is calculated as the ratio of MCA PI to UA PI Doppler and has been hypothesized to be more accurate than its individual components. An association with adverse perinatal outcome has been the focus of several literature reviews. A recent review comparing CPR and UA Doppler measures was undertaken in 30 studies (5046 patients); MCA Doppler and UA Doppler were compared in 38 studies (18,999 patients); and CPR and MCA Doppler were compared in 23 studies (4262 patients). The data showed that sensitivity of CPR outperformed that of UA Doppler, and sensitivity of MCA Doppler performed less well than did those of UA Doppler and CPR. A metaregression analysis was performed to compare the prognostic accuracy of the three tests. The CPR was significantly better than UA Doppler in predicting composite adverse outcome ( P < .001) and emergency delivery for fetal distress ( P = .003) but comparable with UA Doppler in predicting perinatal death ( P = .686), low Apgar score ( P = .595) and NICU admission ( P = .107). MCA Doppler was significantly worse than UA Doppler in predicting low Apgar score ( P = .017) and emergency delivery for fetal distress ( P = .034) and significantly worse than CPR in predicting composite adverse outcome ( P < .001) and emergency delivery for fetal distress ( P = .013) ( Table 21.8 ). Thus it appears that CPR measures, combining information from both the UA and MCA Doppler PIs may have great value in fetal assessment.

The value of MCA Doppler in the prediction of adverse fetal outcome and fetal assessment has been inconsistent. Some studies have suggested that the MCA Doppler measures are useful, whereas others have found poor predictive value. A meta-analysis of 35 eligible studies including 4025 fetuses reviewed the predictive value of MCA Doppler for adverse perinatal outcome. The study reported that low MCA PI appeared to be predictive of impaired fetal well-being assessed by either acidosis (pH < 7.20) at birth, higher likelihood of 5-minute Apgar score lower than 7 (positive likelihood ratio [LR] 1.65 [1.07, 2.52]), or reduced admission to a NICU (positive LR 4.00 [2.16, 7.50]; negative LR 0.62 [0.47, 0.82]). Abnormal MCA PI recording was also predictive of an overall composite measure of adverse perinatal outcome (positive LR 2.77 [1.93, 3.96]; negative LR 0.58 [0.44, 0.69]) and perinatal mortality (positive LR 1.36 [1.10, 1.67]; negative LR 0.51 [0.29, 0.89]). Although these findings suggest that there is an association between abnormal MCA recordings and adverse outcomes, the association is weak.

The potential value of Doppler study of the cerebral circulation in other fetal states is suggested by the demonstration of increased values for PI in the presence of hydrocephalus. This observation is identical to that made postnatally with posthemorrhagic hydrocephalus (see Chapter 28 ) and raises the possibility of the use of Doppler in determination of the need for intervention in fetal hydrocephalus. Changes in cerebral blood flow velocity have also been documented with changes in fetal behavioral states and after administration of indomethacin to the mother.