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Overview of antepartum fetal assessment

Overview of antepartum fetal assessment
Authors:
Caroline Signore, MD, MPH
Catherine Spong, MD
Section Editor:
Vincenzo Berghella, MD
Deputy Editor:
Vanessa A Barss, MD, FACOG
Literature review current through: Jan 2023. | This topic last updated: Apr 28, 2022.

INTRODUCTION — The main techniques for fetal assessment are the nonstress test, biophysical profile, modified biophysical profile, contraction stress test, and fetal movement count. Assessment of amniotic fluid volume (independent of the biophysical profile and modified biophysical profile) and Doppler velocimetry of fetal and funic vessels provide additional information about fetal status. Despite widespread use of these techniques, there is limited evidence to guide their optimal use or demonstrating their effectiveness for improving perinatal outcomes.

This topic will provide an overview of antepartum fetal assessment. Detailed discussions of the various techniques and their use and efficacy for improving perinatal outcome in specific clinical settings are available separately:

(See "Nonstress test and contraction stress test".)

(See "Biophysical profile test for antepartum fetal assessment".)

(See "Decreased fetal movement: Diagnosis, evaluation, and management".)

(See "Assessment of amniotic fluid volume".)

(See "Doppler ultrasound of the umbilical artery for fetal surveillance in singleton pregnancies".)

GOAL — The goals of antepartum fetal assessment are to (1) identify fetuses at risk of intrauterine death or developing neurologic complications from slowly progressive (chronic) intrauterine hypoxia and (2) intervene to prevent these adverse outcomes, if possible.

PHYSIOLOGIC BASIS — Tests for antepartum fetal assessment are based on the premise that the fetus responds to slowly progressive (chronic) hypoxemia with a detectable sequence of biophysical changes, beginning with signs of physiological adaptation and potentially ending with signs of physiological decompensation (figure 1) [1,2]. Studies in animal models support this premise by demonstrating that fetal biophysical activities (eg, heart rate, movement, breathing, tone) are sensitive to fetal oxygen and pH levels, and changes in fetal biophysical activities occur in response to, or in association with, hypoxemia and acidemia [3]. However, fetal biophysical parameters can be affected by factors unrelated to hypoxemia, such as gestational age, maternal medication, maternal smoking, fetal sleep-wake cycles, and fetal disease/anomalies.

Because the sequence of biophysical changes over time described in the figure does not occur in the setting of an acute hypoxemic insult, such as a complete placental abruption, periodic fetal antepartum testing rarely identifies fetuses at risk of death/neurologic complications from an acute insult and thus does not provide an opportunity for intervention to prevent these adverse outcomes.

EFFICACY — Antepartum fetal assessment has had an established role in obstetric practice since the 1970s [4], although its ability to improve pregnancy outcome has not been evaluated by large, well-designed randomized trials [5]. Efficacy is based primarily on two lines of evidence: (1) observational studies that reported lower rates of fetal death in pregnancies that underwent fetal testing than among historic controls with the same indication for testing but no fetal testing and (2) the same or lower rates of fetal death in tested pregnancies (primarily high risk) than in a contemporary untested general obstetric population (primarily low risk) [6-10].

Both of these lines of evidence have obvious limitations [11]. Given multiple advances in maternal and neonatal care over time, contemporary pregnant people can be expected to have better pregnancy outcomes than historic controls, and the better outcomes generally cannot be attributed to the single intervention evaluated in observational studies. Furthermore, the low rate of fetal death in tested pregnancies may be related to more intense prenatal care and intervention in these pregnancies compared with untested pregnancies (Hawthorne effect). Patients undergoing testing may have more provider visits, which are extra opportunities to detect an acute serious maternal or fetal problem, and they are more likely to undergo induction of labor, which can substantially reduce the risk of stillbirth since stillbirth can only occur in ongoing pregnancies.

POTENTIAL BENEFITS AND HARMS — The gaps in the evidence regarding the efficacy of antepartum testing in preventing fetal neurologic injury or death preclude clear conclusions about the benefits and harms of antepartum testing and a clear understanding of its costs.

Potential benefits:

If effective (see 'Efficacy' above), the major benefit would be the ability to identify fetuses in whom appropriate timely intervention would prevent death or adverse neurologic outcomes.

Potential harms:

The major harm would be false-positive tests that lead the provider to unnecessary additional fetal evaluation and/or intervention (particularly iatrogenic preterm birth).

False-negative tests that do not alert the provider to the need for further fetal evaluation and/or intervention is another potential harm.

A theoretic concern is that cerebral palsy and stillbirth may share a common etiologic pathway since they have some common risk factors (eg, fetal growth restriction, congenital anomalies, fetal hypoxia) [12]. If true, identification and prompt delivery of fetuses with nonreassuring antenatal testing may allow those with neurologic injury who would have died in utero to survive with permanent neurologic impairment.

Uncertain effects:

Little is known about the effects of antenatal testing on maternal mental states. Antenatal testing may provoke anxiety but can also offer reassurance of fetal well-being when the tests are normal [13].

Potential costs include the actual dollars spent on tests and their interpretation, opportunity costs of patients' and practitioners' time spent in testing, and maternal and infant morbidity (or even mortality) from iatrogenic delivery because of abnormal results, especially given the frequency of false-positive tests.

INDICATIONS FOR FETAL ASSESSMENT — The American College of Obstetricians and Gynecologists' (ACOG) practice bulletin on antepartum fetal assessment is the good practice standard in the United States [14]. The bulletin suggests antepartum testing for pregnancies in which the risk of antepartum fetal demise is increased, which ACOG has defined as a stillbirth rate greater than 0.8 per 1000 and associated with a relative risk (RR) or odds ratio for stillbirth >2.0 compared with pregnancies without the condition [15]. This stillbirth rate was chosen because it is the false negative rate of the biophysical profile.

It is not possible to list every clinical setting where tests for antepartum fetal assessment might be useful to identify fetuses at risk of intrauterine demise or other complications of asphyxia. The more common clinical settings in which antepartum fetal testing is typically performed are listed below and discussed in more detail in individual reviews on each topic.

Diabetes – Preexisting or gestational diabetes treated with pharmacotherapy. Gestational diabetes in which glucose levels are normal on nutritional therapy does not appear to be associated with an increased risk of stillbirth, so antepartum fetal testing can be omitted. (See "Gestational diabetes mellitus: Obstetric issues and management", section on 'Fetal surveillance' and "Pregestational (preexisting) diabetes mellitus: Obstetric issues and management", section on 'Initiation and frequency of fetal surveillance'.)

Hypertensive disorders – Chronic hypertension or pregnancy-related hypertension. (See "Preeclampsia: Antepartum management and timing of delivery", section on 'Assessment of fetal well-being' and "Gestational hypertension", section on 'Fetal assessment' and "Chronic hypertension in pregnancy: Prenatal and postpartum care", section on 'Tests to monitor fetal well-being'.)

Fetal growth restriction – (See "Fetal growth restriction: Pregnancy management and outcome", section on 'Doppler ultrasonography, nonstress test/cardiotocography, and biophysical profile'.)

Twin pregnancy – (See "Twin pregnancy: Routine prenatal care", section on 'Antepartum fetal testing' and "Twin pregnancy: Overview".)

Postterm pregnancy – Testing is often initiated between 41+0 and 42+0 weeks of gestation but may be initiated at estimated gestational age of 39+0 to 40+0 weeks in a suboptimally dated pregnancy [16]. (See "Postterm pregnancy", section on 'Alternative approach: Expectant management with fetal monitoring'.)

Decreased fetal activity – (See "Decreased fetal movement: Diagnosis, evaluation, and management".)

Systemic lupus erythematosus – (See "Pregnancy in women with systemic lupus erythematosus", section on 'Maternal-fetal monitoring'.)

Antiphospholipid syndrome – (See "Antiphospholipid syndrome: Obstetric implications and management in pregnancy", section on 'Antepartum maternal and fetal monitoring'.)

Sickle cell disease – (See "Sickle cell disease: Obstetric considerations", section on 'Maternal care'.)

Alloimmunization to red blood cell antigens – (See "RhD alloimmunization in pregnancy: Management", section on 'MCA-PSV ≤1.5 MoMs for gestational age' and "Management of non-RhD red blood cell alloantibodies during pregnancy", section on 'Prenatal management'.)

Oligohydramnios or polyhydramnios – (See "Polyhydramnios: Etiology, diagnosis, and management", section on 'All patients'.)

Prior fetal demise – (See "Stillbirth: Incidence, risk factors, etiology, and prevention", section on 'Strategies for prevention of recurrent stillbirth'.)

Preterm prelabor rupture of membranes – Preterm prelabor rupture of membranes may be associated with oligohydramnios and possibly subclinical intrauterine infection. The goal of antenatal testing in this setting is early recognition of intraamniotic infection necessitating delivery. (See "Preterm prelabor rupture of membranes: Management and outcome", section on 'Fetal monitoring'.)

An ACOG Committee Opinion on indications for outpatient antenatal fetal surveillance provides a list of potential maternal, fetal, placental, and obstetric indications (table 1) [15]. The American College of Radiology Appropriateness Criteria for assessment of fetal well-being also provide a broad list of conditions that the American College of Radiology believes may warrant judicious use of tests of fetal well-being [17].

Possible indications for antenatal testing — Epidemiologic data suggest a small increased risk of fetal demise associated with a number of additional conditions, including:

Advanced maternal age. (See "Management of pregnancy in patients of advanced age".)

Obesity. (See "Obesity in pregnancy: Complications and maternal management".)

Major fetal structural anomalies [18] (refer to topics on individual anomalies).

Abnormalities in first- and second-trimester maternal biochemical trisomy 21 (Down syndrome) screening results [19,20].

Whether a policy of antenatal testing in pregnancies with these risk factors can reduce the incidence of fetal demise or fetal injury is unknown. The use of fetal testing in these pregnancies is decided on a case-by-case basis.

FETAL ASSESSMENT TECHNIQUES

Fetal movement counting — Objective maternal assessment of fetal movements ("fetal kick counts") is based on evidence that fetal movement decreases in response to fetal hypoxemia [21]. Although there is universal consensus opinion that patients with decreased fetal movement should undergo further fetal assessment, available evidence does not support a clear fetal movement threshold or "alarm limit" indicating when the risk of fetal death or injury is increased and randomized trials of fetal movement counting for assessment of fetal well-being found no conclusive evidence of a benefit of this intervention. The available evidence, as well as approaches for counseling pregnant patients about how and when to monitor fetal activity and evaluation of those with decreased fetal activity can be found separately. (See "Decreased fetal movement: Diagnosis, evaluation, and management".)

Cardiotocographic techniques

Nonstress test — The nonstress test (NST) was developed as a result of observations that (1) the presence of two or more fetal heart rate (FHR) accelerations during a contraction stress test (CST) often predicted a negative CST, and (2) the absence of accelerations on a baseline FHR tracing was associated with adverse perinatal outcomes [4]. FHR accelerations, spontaneous or provoked (eg, by vibroacoustic stimulation), are a good indicator of normal fetal autonomic function and absence of acidosis and neurologic depression. Although a meta-analysis of randomized trials found no clear evidence that antenatal cardiotocography improved perinatal outcome, the quality of evidence was low or very low [22]. These data, as well as NST interpretation and use, are described in detail separately. (See "Nonstress test and contraction stress test", section on 'Nonstress test'.)

The main advantage of the NST over the CST is that it does not require an intravenous line, oxytocin, or contractions. Disadvantages are that the false-negative and false-positive rates are higher than for the CST (a false-negative NST is when an antepartum stillbirth occurs within one week of a reactive test; a false-positive NST is a nonreactive test that is followed by a normal back-up test, such as a negative CST or high biophysical profile [BPP] score) (table 2) [6,23]. (See "Nonstress test and contraction stress test", section on 'Nonstress test'.)

Nonstress test with assessment of amniotic fluid — Sonographic assessment of amniotic fluid volume (AFV) is often performed as an adjunct to the NST to improve sensitivity (ie, decrease the rate of false-negative reactive tests). Only low-quality data support this hypothesis. A small retrospective study reported pregnancies with reactive NSTs and low amniotic fluid index (0 to 5 cm) were at increased risk for meconium passage and five-minute Apgar score <7 at delivery compared with those with a normal amniotic fluid index [24]. A study in postterm pregnancies reported decreased AFV and variable decelerations were associated with an increased incidence of fetal distress, even when the NST was reactive, but the performance of the combined test was similar to that of either test alone [25]. (See 'Assessment of amniotic fluid volume' below.)

Contraction stress test — The CST is based on the fetal response to a transient reduction in fetal oxygen delivery during uterine contractions. If the fetus becomes hypoxemic (fetal arterial pO2 below 20 mmHg [26,27]), reflex slowing of the FHR occurs, which can manifest clinically as late decelerations (waveform 1 and waveform 2). The change in the FHR is mediated by fetal chemoreceptors and baroreceptors and by parasympathetic and sympathetic fibers to the heart and cerebral vessels. Performance of the CST, as well as its interpretation and use, are described in detail separately. (See "Nonstress test and contraction stress test", section on 'Contraction stress test'.)

The CST is seldom performed given the wide availability of other tests (eg, NST, BPP) that do not have its major drawbacks: the need to stimulate contractions with intravenous oxytocin, the contraindication to inducing contractions in some conditions (eg, placenta previa), and the high false-positive rate (ie, fetus goes on to tolerate labor without FHR changes necessitating intervention). However, the false-negative rate (ie, rate of fetal death within one week of a negative test) is very low (table 2), thus providing reassurance of adequate fetal oxygenation after a normal test result [28].

Sonographic techniques

Biophysical profile — The BPP combines the NST with ultrasonographic fetal assessment by assigning points to the following parameters: fetal breathing movements, fetal body movements, reflex/tone/flexion-extension movements, and AFV (table 3) [29]. Thus, this test assesses indicators of both acute hypoxia (NST, breathing, body movement, tone) and chronic hypoxia (AFV). The BPP score has a direct linear correlation with fetal pH (figure 2).

The modified biophysical profile (mBPP) consists of the NST as a measure of acute oxygenation and assessment of AFV as a measure of longer-term oxygenation. The mBPP is considered abnormal if the NST is nonreactive, no single deepest vertical pocket of amniotic fluid ≥2 cm is present, or both.

The false-negative rates for the BPP and mBPP are very low, but the false-positive rates are high (table 2) (a false-negative BPP or mBPP is when an antepartum stillbirth occurs within one week of a high score; a false positive is a low score that is followed by a normal back-up test). Performance of the BPP and mBPP are described in detail separately. (See "Biophysical profile test for antepartum fetal assessment".)

Assessment of amniotic fluid volume — In the hypoxemic fetus, cardiac output is redirected to the brain, heart, and adrenals and away from less vital organs, such as the kidney; the reduction in renal perfusion leads to decreased fetal urine production, which may result in decreased AFV (oligohydramnios) over time. This is the main rationale for assessment of AFV as an adjunct to the NST and as a routine component of the BPP. FHR abnormalities may be observed since cord compression is more likely in the setting of oligohydramnios. (See "Oligohydramnios: Etiology, diagnosis, and management in singleton gestations".)

AFV can be assessed qualitatively or quantitatively. The single deepest pocket and the amniotic fluid index method are commonly used methods of assessment and equivalent in their prediction of adverse outcome in singleton pregnancies. Assessment of AFV, as well as its interpretation and use, is described in detail separately. (See "Assessment of amniotic fluid volume".)

Doppler velocimetry

Overview — Measurement of blood flow velocities in the maternal and fetal vessels provides information about uteroplacental blood flow and fetal responses to physiologic challenges. Abnormal vascular development of the placenta, such as in preeclampsia, results in progressive hemodynamic changes in the fetoplacental circulation. Doppler indices from the umbilical artery increase when 60 to 70 percent of the placental vascular tree is compromised [30]; eventually, fetal middle cerebral artery impedance falls and fetal aortic resistance rises to preferentially direct blood to the fetal brain and heart [31,32]. Ultimately, end diastolic flow in the umbilical artery ceases or reverses and resistance increases in the fetal venous system (ductus venosus, inferior vena cava) [2,32-34]. These changes occur over variable periods of time and correlate with fetal acidosis [35].

In contrast to most other methods of fetal assessment, Doppler-based tests have been rigorously evaluated in randomized trials. The information derived from velocity waveforms varies according to the specific vessel interrogated. Umbilical artery Doppler is the most common Doppler technique used for fetal assessment where fetal hypoxemia is a concern. Fetal middle cerebral artery-peak systolic velocity (MCA-PSV) is the best tool for predicting fetal anemia in at-risk pregnancies.

Umbilical artery — Umbilical artery Doppler assessments are most useful for monitoring fetuses with early-onset growth restriction due to uteroplacental insufficiency [36]. The umbilical artery waveform pattern is compatible with a low-resistance system: forward blood flow occurs throughout the cardiac cycle. Umbilical artery flow velocity waveforms of normally growing fetuses are characterized by high-velocity diastolic flow, whereas in growth-restricted fetuses, umbilical artery diastolic flow is diminished, absent, or even reversed in severe cases [37]. This progressive reduction of umbilical artery diastolic flow is associated with increasing obliteration of tertiary villi [38]. In the growth-restricted fetus, absent or reversed end diastolic flow is associated with fetal hypoxemia and acidemia, and increased perinatal morbidity and mortality [34,38,39]. The technique for Doppler interrogation of the umbilical artery, as well as interpretation and use of umbilical artery Doppler, is described in detail separately. (See "Doppler ultrasound of the umbilical artery for fetal surveillance in singleton pregnancies".)

The American College of Obstetricians and Gynecologists' practice guidelines support the use of umbilical artery Doppler assessments in the management of suspected fetal growth restriction, but not for normally grown fetuses [14]. When monitoring the growth-restricted fetus, umbilical artery Doppler should be used with standard fetal assessment (NST and/or BPP score). In a systematic review of 16 randomized trials including over 10,000 high-risk patients where the definition of "high risk" varied among trials, use of Doppler ultrasound resulted in a variable decrease in perinatal mortality (perinatal mortality: 1.2 versus 1.7 percent, odds ratio 0.71, 95% CI 0.52-0.98, number needed to treat 203) [40]. (See "Fetal growth restriction: Evaluation", section on 'Umbilical artery Doppler'.)

There is no strong evidence to support umbilical artery Doppler assessment in settings other than suspected fetal growth restriction. In a systematic review of five randomized trials including over 14,000 low-risk or unselected obstetric patients, routine umbilical artery Doppler screening did not improve perinatal outcomes [41].

Middle cerebral artery — Doppler assessment of the fetal middle cerebral artery-peak systolic velocity (MCA-PSV) is the best tool for monitoring for fetal anemia in at-risk pregnancies, such as those affected by RhD alloimmunization. (See "RhD alloimmunization in pregnancy: Management", section on 'Assess for severe anemia using MCA-PSV in fetuses at risk'.)

MCA Doppler is under investigation as an additional tool for assessment of pregnancies complicated by growth restriction. Its use in this setting is based on the premise that systemic blood flow in these fetuses is redistributed from the periphery to the brain and Doppler measurement of flow velocity in the fetal MCA can detect this brain-sparing effect [31,42-44]. Specifically, the cerebroplacental ratio, calculated by dividing the Doppler indices of the MCA by the umbilical artery, is emerging as a potential predictor of adverse outcome for both growth-restricted and appropriately-grown fetuses [45].

Venous system — Venous Doppler parameters may be abnormal due to several abnormalities in cardiovascular function. These include decreased cardiac compliance and contractility, marked elevations in cardiac afterload, and abnormalities of cardiac rhythm and rate. The clinical utility of venous Doppler velocimetry is therefore greatest in fetal conditions with cardiac manifestations and/or marked placental insufficiency. These conditions include fetal growth restriction due to placental insufficiency, twin-twin transfusion, fetal hydrops [46,47], and fetal arrhythmia. (See "Twin-twin transfusion syndrome: Screening, prevalence, pathophysiology, and diagnosis" and "Twin-twin transfusion syndrome: Management and outcome" and "Fetal arrhythmias" and "Fetal growth restriction: Evaluation", section on 'Ductus venosus Doppler'.)

The fetal precordial veins (ductus venosus and inferior vena cava) and the umbilical vein are the vessels most commonly evaluated in clinical practice, although flow velocity waveforms have been reported for many other venous vessels. Blood flow in the umbilical vein is continuous in normal pregnancies >15 weeks of gestation. In pathological states, such as fetal growth restriction, flow in the umbilical vein may be pulsatile, which reflects cardiac dysfunction related to increased afterload. The ductus venosus regulates oxygenated blood in the fetus [48] and is resistant to alterations in flow except in the most severely growth-restricted fetuses.

Uterine artery — A number of investigators have explored the use of uterine artery Doppler for third-trimester fetal assessment among patients with complicated pregnancies, but its role in these settings has not been clearly defined [49-51]. Impedance to flow in the uterine arteries normally decreases as pregnancy progresses. Failure of adequate trophoblast invasion and remodeling of maternal spiral arteries is characterized by a persistent high-pressure uterine circulation and increased impedance to uterine artery blood flow. Elevated resistance indices and/or persistent uterine artery notching at 22 to 24 weeks of gestation indicate reduced blood flow in the maternal compartment of the placenta and have been associated with development of preeclampsia, fetal growth restriction, and perinatal death [52]. (See "Fetal growth restriction: Screening and diagnosis" and "Early pregnancy prediction of preeclampsia", section on 'Uterine artery Doppler velocimetry'.)

CHOICE OF TEST — Although observational studies have described the use of the nonstress test (NST), contraction stress test (CST), and biophysical profile score (BPP) for monitoring high-risk pregnancies, no method has been evaluated in well-designed randomized trials, and it is not clear which method, if any, is superior. The choice depends on multiple factors, including gestational age (up to 50 percent of NSTs are not reactive in healthy 24- to 28-week fetuses [53]), availability, desire for fetal biometry or follow-up of a congenital anomaly, ability to monitor the fetal heart rate (eg, the NST and CST may not be interpretable in a fetus with an arrhythmia), and cost.

Doppler assessment of the umbilical artery should be used to monitor the growth-restricted fetus, given its proven efficacy in reducing perinatal death in this setting when used with standard fetal testing (NST, BPP) and appropriate intervention [54]. It has only modest ability to predict fetal compromise in other high-risk pregnancies [55]. (See "Doppler ultrasound of the umbilical artery for fetal surveillance in singleton pregnancies" and "Fetal growth restriction: Pregnancy management and outcome", section on 'Fetal surveillance'.)

TIMING — Testing should begin as soon as an increased risk of fetal demise is identified and delivery for perinatal benefit would be considered if test results are abnormal.

In the general obstetric population, observational data show that rate of stillbirth in non-growth-restricted fetuses significantly rises between approximately 32 to 34 weeks and term [56]. Based on these data and data from large series of high-risk pregnancies [57-59], 32 weeks has become a common threshold for initiating fetal assessment when a condition potentially associated with a late preterm or term stillbirth is present. Testing is initiated before 32 weeks when the pregnancy is complicated by multiple high-risk conditions or a condition with a high risk of fetal demise before 32 weeks (eg, severe growth restriction) is present. In such cases, testing is initiated at the gestational age at which delivery for perinatal benefit would be considered if test results are abnormal.

(See "Nonstress test and contraction stress test" and "Biophysical profile test for antepartum fetal assessment" and "Decreased fetal movement: Diagnosis, evaluation, and management".)

FOLLOW-UP OF PREGNANCIES WITH NORMAL TEST RESULTS

Negative predictive value of a normal test result — The negative predictive value for stillbirth within one week of a normal test ranges from 99.8 to 100 percent [14]. A normal test result for the nonstress test (NST), contraction stress test, or biophysical profile is reassuring that the fetus is at low risk of antepartum stillbirth proximate to testing and in the absence of development of an acute maternal or fetal disorder, such as placental abruption or cord compression.

Follow-up of pregnancies with a normal result and a transient condition as indication for testing — A single normal test result without follow-up testing is adequate if the test was performed for a nonrecurring indication in an otherwise low-risk pregnancy (eg, reactive NST after a minor motor vehicle accident and no signs of labor or vaginal bleeding).

Follow-up of pregnancies with a normal result and a chronic condition as indication for testing — There are no data from randomized trials on which to base recommendations for the optimum frequency of fetal monitoring (daily, every other day, twice per week, once per week) in pregnancies with an ongoing indication for fetal testing. These decisions are based on expert opinion, clinical experience with similar high-risk pregnancies, and community standards.

Testing is typically performed weekly in pregnancies at modestly increased risk of fetal demise because of an ongoing maternal or fetal disorder (see 'Indications for fetal assessment' above), but the frequency is often increased to two to seven times per week:

If a change in pregnancy status occurs (eg, fetal growth percentile falls from 10th percentile to 3rd percentile, worsening preeclampsia).

In clinical settings considered to be very high risk for fetal demise (eg, fetal growth restriction with absent or reversed diastolic flow, hydrops fetalis, patients with preeclampsia with severe features who are not being induced, preterm prelabor rupture of membranes).

At 36 weeks of gestation. As the risk of stillbirth increases with advancing gestational age, testing may begin weekly at 32 weeks and then increased to twice per week at 36 weeks.

Fetuses with normal results are tested until the onset of labor. In the absence of spontaneous labor, the decision to continue antepartum testing versus induction of labor (or scheduled cesarean delivery) depends on the indication for testing. For example, patients with preeclampsia without features of severe disease are routinely delivered at 37 weeks of gestation (see "Preeclampsia: Antepartum management and timing of delivery", section on 'Timing of delivery'). Pregnant patients undergoing testing for conditions only modestly associated with an increased risk of stillbirth, such as advanced maternal age or obesity without comorbidities, might prefer induction at 39 weeks of gestation rather than expectant management plus fetal testing since the risk of stillbirth is lower with induction [11].

MANAGEMENT OF PREGNANCIES WITH ABNORMAL TEST RESULTS — The clinical setting needs to be considered, as described below.

Transient condition as cause of abnormal test — If a temporary maternal condition, such as diabetic ketoacidosis or acute bronchospasm, may account for the abnormal test result, prompt treatment of the maternal condition may also improve fetal oxygenation and lead to a normal test result on subsequent testing. Similarly, if a maternal medication is likely affecting fetal behavior or heart rate, then withholding the drug (if possible) and repeating the test when the effects have dissipated will allow a clearer assessment of fetal status. If the repeat test becomes normal, follow-up is as described above. (See 'Follow-up of pregnancies with normal test results' above.)

Chronic condition as cause of abnormal result — Given the high rate of false-positive tests (table 2) and the high negative predictive value of a normal test, an abnormal test result is generally followed by additional testing with a different test (eg, contraction stress test [CST] or biophysical profile [BPP] after a nonreactive nonstress test [NST]) to provide more information about fetal status. However, clinical judgment should guide decision making regarding delivery versus follow-up testing after an abnormal test result, taking into account a combination of factors, as described below.

Gestational age (eg, lower threshold for delivery at term versus preterm).

Severity of maternal and fetal disease (eg, low threshold for delivery for hydrops fetalis, for diabetes with poor glycemic management versus good glycemic management, or for fetal growth restriction at 3rd percentile with oligohydramnios and abnormal umbilical artery Doppler flow versus 10th percentile with normal amniotic fluid volume and normal umbilical artery Doppler flow).

Progression of disease (eg, low threshold for delivery when fetal growth falls from the 10th percentile to the 3rd percentile versus stable or slow but progressive growth).

Other available information (eg, low threshold for delivery when late or variable decelerations, absent variability, or a prolonged deceleration on a nonreactive NST; BPP score 0 versus 4 or 6; absence of accelerations on a positive CST; intrauterine growth restriction with absent or reversed Doppler flow in umbilical artery).

Route of delivery — If delivery is indicated by the specific clinical setting and abnormal test results, induction of labor is not contraindicated. For example, after a positive CST, up to 40 percent of fetuses tolerate labor without fetal heart rate changes necessitating intervention [60]. Similarly, a BPP score of 0/10 does not exclude the possibility of a trial of labor if the baseline fetal heart rate and variability are normal and decelerations are absent. However, cesarean birth rather than a trial of induction is usually indicated for a category III tracing. (See "Intrapartum category I, II, and III fetal heart rate tracings: Management", section on 'Category III pattern: Abnormal'.)

In most cases, the decision to attempt a trial of labor is a clinical judgment that must take into account the full clinical scenario, as described above (see 'Chronic condition as cause of abnormal result' above), as well as whether labor is likely to be relatively short or long. A fetus with abnormal antepartum testing should have continuous electronic fetal monitoring during labor and may have a normal intrapartum fetal heart rate tracing during a short labor, but may not be able to tolerate a long labor. A long labor is more likely in nulliparous patients, at earlier gestational ages, with unfavorable cervical status, and in multiparous patients with no prior vaginal births.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Fetal surveillance".)

SUMMARY AND RECOMMENDATIONS

Goal: The goal of antepartum fetal assessment is to identify the fetus that will benefit from early intervention, such as in utero resuscitation or delivery, and thereby prevent fetal death or neurologic injury. (See 'Introduction' above.)

Physiologic basis: Antepartum testing is based on the premise that the fetus responds to hypoxemia with a detectable sequence of biophysical changes (figure 1). (See 'Physiologic basis' above.)

Efficacy: Antepartum fetal assessment has had an established role in obstetric practice since the 1970s, although its ability to improve pregnancy outcome has not been evaluated by large, well-designed randomized trials. Efficacy is based on (1) observational studies that reported lower rates of fetal death in pregnancies that underwent fetal testing than among historic controls with the same indication for testing but no fetal testing and (2) the same or lower rates of fetal death in tested pregnancies (primarily high risk) than in a contemporary untested general obstetric population (primarily low risk). (See 'Efficacy' above.)

Patient selection: Antepartum fetal testing is indicated in pregnancies in which the risk of antepartum fetal demise is increased. The American College of Obstetricians and Gynecologists (ACOG) defined this as a stillbirth rate greater than 0.8 per 1000 and associated with a relative risk or odds ratio for stillbirth >2.0 compared with pregnancies without the condition. ACOG also provided a list of potential maternal, fetal, placental, and obstetric indications (table 1). (See 'Indications for fetal assessment' above.)

Tests:

Techniques for assessment of fetal well-being (nonstress test, contraction stress test, biophysical profile, modified biophysical profile) are described in the table (table 2). (See 'Fetal assessment techniques' above.)

The optimal choice of technique(s) for fetal assessment has not been determined and depends on multiple factors, including gestational age, availability, desire for fetal biometry or follow-up of a congenital anomaly, ability to monitor the fetal heart rate, and cost. The best evidence supports umbilical artery Doppler assessment for monitoring fetuses with early-onset growth restriction due to uteroplacental insufficiency, given its proven efficacy in reducing perinatal death in this setting when used with standard fetal testing (nonstress test, biophysical profile score) and appropriate intervention. (See 'Choice of test' above.)

Timing and frequency:

Antepartum fetal assessment is initiated at the gestational age when an increased risk of fetal demise is identified and delivery for perinatal benefit would be considered if test results are abnormal. In most pregnancies, this is at 32 weeks of gestation. (See 'Timing' above.)

Testing is typically performed weekly, but the frequency is generally increased if there is a change in pregnancy status or in clinical settings considered to be very high risk. (See 'Follow-up of pregnancies with normal test results' above.)

Interpretation: An abnormal test result is generally followed by additional testing with a different test, given the high rate of false-positive results (table 2). The clinical setting also needs to be considered. If a temporary maternal condition may account for the abnormal test result, prompt treatment of the maternal condition may also improve fetal oxygenation and lead to a normal test result on subsequent testing. In chronic conditions, clinical judgment guides management and needs to consider case specific factors. (See 'Management of pregnancies with abnormal test results' above.)

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