Determination of Gestational Age

The mean duration of a singleton pregnancy is 280 days (40 weeks) from the first day of the last normal menstrual period in women with regular 28-day menstrual cycles. Term, defined as the period from 37 weeks’ (259 days’) to 42 weeks’ (294 days’) gestation, is the optimal time for delivery. However, both preterm births (defined as delivery before 37 weeks’ gestation) and postterm births (delivery after 42 weeks’ gestation) are associated with increased perinatal and neonatal morbidity and mortality, with variation occurring within this 5-week gestational age range. For this reason, the designations of early term (37 0/7 to 38 6/7 weeks’ gestation), full term (39 0/7 to 40 6/7 weeks’ gestation), and late term (41 0/7 to 41 6/7 weeks’ gestation) were adopted. Evaluation of fetal growth, efficient use of screening and diagnostic tests, appropriate initiation of fetal surveillance, and optimal timing of delivery all depend on accurate dating of the pregnancy.

Recommendations for determining the gestational age and estimated due date (EDD) have been established by the American College of Obstetricians and Gynecologists, the Society for Maternal-Fetal Medicine, and the American Institute of Ultrasound in Medicine ( Box 6.1 ). Determination of gestational age is most accurate when ultrasonographic measurement of the fetus or embryo is performed in the first trimester (up to and including 13 6/7 weeks’ gestation). For pregnancies achieved by assisted reproductive technology (ART), the EDD should be assigned based on the age of the embryo and the date of transfer. Importantly, the EDD should be determined as soon as the last menstrual period (LMP) is recorded and the first accurate ultrasonographic examination is performed, and the EDD should be communicated to the patient and documented in the medical record. Assigning the EDD by the first day of the LMP is limited by inaccurate recall of the LMP, irregular cycle length, and variation in the timing of ovulation. One study reported that reliance on LMP alone leads to a false diagnosis of preterm birth and postterm pregnancy in one-fourth and one-eighth of cases, respectively. For these reasons, ultrasonographic measurement of the embryo or fetus can improve the accuracy of the EDD, even when the LMP is known, and the earlier in pregnancy the ultrasonographic examination is performed, the greater the accuracy. In the first trimester, before 14 0/7 weeks’ gestation, the mean of three crown-rump length (CRL) measurements should be used to establish or confirm the gestational age. In the second and third trimesters, at 14 0/7 weeks’ gestation and beyond, biometric measurements should be used for dating. Measurements of the biparietal diameter, head circumference, femur length, and the abdominal circumference are used in a regression formula to calculate the gestational age and EDD. Assessment of gestational age in the third trimester (28 0/7 weeks’ gestation and beyond) is the least accurate. Guidelines for revising the EDD of pregnancy are based on the initial ultrasonographic examination. If the CRL dating differs by more than 5 days from the LMP dating before 9 0/7 weeks’ gestation, then the EDD should be revised based on the CRL measurement. A difference of greater than 7 days between 9 0/7 and 15 6/7 weeks’ gestation, greater than 10 days between 16 0/7 and 21 6/7 weeks’ gestation, greater than 14 days between 22 0/7 and 27 6/7 weeks’ gestation, and greater than 21 days at 28 0/7 weeks’ gestation and beyond should be revised based on the ultrasonographic examination.

Because the accuracy of gestational age assessment decreases with increasing gestational age, pregnancies without an ultrasonographic examination confirming or revising the EDD before 22 0/7 weeks’ gestation should be considered suboptimally dated. These pregnancies may benefit from a follow-up ultrasonographic examination 3 to 4 weeks after the initial ultrasonographic examination to confirm gestational age and assess interval growth to screen for fetal growth restriction.

Importantly, once the EDD is established it should rarely be revised, as discrepancies between gestational age and fetal measurements could indicate an abnormality in fetal growth, such as macrosomia or fetal growth restriction.

Routine Ultrasonography

An ultrasonographic examination is recommended for all pregnancies, given its ability to accurately determine gestational age, viability, fetal number, and placental location, and screen for fetal structural abnormalities in the second trimester.

Some studies have shown an improvement in perinatal outcome with the use of ultrasonography. In a prospective trial of 9310 low-risk women randomly assigned to an ultrasonographic examination for screening at 16 to 20 weeks’ gestation or for obstetric indications only, a significantly lower perinatal mortality rate was observed in the group undergoing screening (4.6 vs. 9.0 per 1000 births, respectively). The screening examination allowed for earlier detection of major fetal malformations and multiple gestations, which enabled more appropriate care, and improved pregnancy dating and a lower rate of labor inductions for postterm pregnancies. In contrast, a subsequent large multicenter randomized clinical trial involving 15,151 low-risk women in the United States, designated the RADIUS study, concluded that screening ultrasonography did not improve perinatal outcomes and had no impact on the management of the anomalous fetus. Although this trial was adequately powered, the highly selective entry criteria (less than 1% of pregnant women in the United States would have been eligible) and inappropriate primary outcomes for a low-risk population (perinatal morbidity and mortality) have been criticized. Importantly, in the routine ultrasonography group, only 17% of major congenital anomalies were detected before 24 weeks’ gestation. There is significant variability in the sensitivity of routine ultrasonographic examinations for the detection of fetal anomalies; in a large review of 36 studies with over 900,000 fetuses, the detection rate for fetal anomalies ranged from 15% to 80%. The detection rates for malformations are improved when performed by an experienced operator at a tertiary center, are higher for central nervous system and urinary tract versus cardiac anomalies, and are lower in patients with a high body mass index (BMI).

Evaluation of Fetal Growth

Normal fetal growth is a critical component of a healthy pregnancy and the subsequent long-term health of the child. An increased risk for delivering a small-for-gestational-age baby and/or having a preterm delivery is associated with low maternal gestational weight gain, while a higher risk for delivering a large-for-gestational-age baby and/or cesarean delivery is associated with excessive gestational weight gain. The current recommendations for maternal weight gain in pregnancy were revised by the Institute of Medicine (IOM) in 2009 and are based on maternal prepregnancy BMI ( Table 6.1 ). The guidelines recommend that: (1) underweight and normal weight women gain approximately 1 pound (0.5 kg) per week in the second and third trimesters; (2) overweight and obese women gain approximately one-half pound (0.25 kg) per week in the second and third trimesters; and (3) all women try to be within the normal BMI range when they conceive.

The size, presentation, and lie of the fetus can be assessed with abdominal palpation. A systematic method of examination of the gravid abdomen was first described by Leopold and Sporlin in 1894. Although the abdominal examination has several limitations (especially in the setting of a small fetus, maternal obesity, multiple pregnancy, uterine fibroids, or polyhydramnios), it is safe, is well tolerated, and may add valuable information to assist in antepartum management. Palpation is divided into four separate Leopold maneuvers ( Fig. 6.1 ). Each maneuver is designed to identify specific fetal landmarks or to reveal a specific relationship between the fetus and mother. The first maneuver, for example, involves measurement of the fundal height. The uterus can be palpated above the pelvic brim at approximately 12 weeks’ gestation. Thereafter, fundal height should increase by approximately 1 cm per week, reaching the level of the umbilicus at 20 to 22 weeks’ gestation ( Fig. 6.2 ). Between 20 and 32 weeks’ gestation, the fundal height (in centimeters) is approximately equal to the gestational age (in weeks) in healthy women of average weight with an appropriately growing fetus. However, there is a wide range of normal fundal height measurements. In one study, a 6-cm difference was noted between the 10th and 90th percentiles at each week of gestation after 20 weeks. Moreover, maximal fundal height occurs at approximately 36 weeks’ gestation, after which time the fetus drops into the pelvis in preparation for labor. For all of these reasons, reliance on fundal height measurements alone fails to identify more than 50% of fetuses with fetal growth restriction (also known as intrauterine growth restriction). Serial fundal height measurements by an experienced obstetric care provider are more accurate than a single measurement and will lead to better diagnosis of fetal growth restriction, with reported sensitivities as high as 86%.

Leopold maneuvers for palpation of the gravid abdomen.

Fundal height measurements in a singleton pregnancy with normal fetal growth.

If clinical findings suggest a fetal growth discrepancy between size and dates, ultrasonography is the modality of choice to evaluate and offer alternative explanations, such as multifetal pregnancy, polyhydramnios, fetal demise, and uterine fibroids. For many years, obstetric ultrasonography has used fetal biometry to define fetal size by weight estimations. This approach has a number of limitations. First, regression equations used to create weight estimation formulas are derived primarily from cross-sectional data for infants being delivered within an arbitrary period after the ultrasonographic examination. Second, these equations assume that body proportions (fat, muscle, bone) are the same for all fetuses. Finally, growth curves for “normal” infants between 24 and 37 weeks’ gestation rely on data collected from pregnancies delivered preterm, which are abnormal and probably complicated by some element of uteroplacental insufficiency, regardless of whether the delivery was spontaneous or iatrogenic. Despite these limitations, if the gestational age is well validated, the prevailing data suggest that prenatal ultrasonography can be used to verify an alteration in fetal growth in 80% of cases and to exclude abnormal growth in 90% of cases.

Ultrasonographic estimates of fetal weight are commonly derived from mathematical formulas that use a combination of fetal measurements, especially the biparietal diameter, abdominal circumference, and femur length. The abdominal circumference is the single most important measurement and is weighted more heavily in these formulas. Unfortunately, the abdominal circumference is also the most difficult measurement to acquire, and small differences in the measured value result in large changes in the estimated fetal weight (EFW). The accuracy of the EFW depends on a number of variables, including gestational age (in absolute terms, EFW is more accurate in preterm or growth-restricted fetuses than in term or macrosomic fetuses), operator experience, maternal body habitus, and amniotic fluid volume (ultrasound measurements are more difficult to acquire if the amniotic fluid volume is low). The EFW may differ from the birthweight by up to 20% in 95% of cases, and greater than 20% in the remaining cases. Indeed, an ultrasonographic EFW at term is no more accurate than a clinical estimate of fetal weight made by an experienced obstetric care provider or the mother’s estimate of fetal weight if she has delivered before. Ultrasonographic estimates of fetal weight must therefore be evaluated within the context of the clinical situation and balanced against the clinical estimates. Serial ultrasonographic evaluations of fetal weight are more useful than a single measurement in diagnosing abnormal fetal growth. The ideal interval for fetal growth evaluations is every 3 to 4 weeks, because more frequent determinations may be misleading due to variations in the ultrasonographic measurements; however, in some cases, such as with fetuses suspected of growth restriction, evaluations can be performed every 2 weeks. The use of population-specific fetal growth curves based on maternal (e.g., weight or race ) or environmental factors have been demonstrated to improve the accuracy of ultrasonographic EFW, particularly in the setting of abnormal fetal growth. For example, growth curves derived from a population that lives at high altitude, where the fetus is exposed to lower oxygen tension, will be different from those derived from a population at sea level. However, the use of customized fetal growth curves has not yet been shown to improve outcomes. Abnormal fetal growth can be classified as insufficient (fetal growth restriction) or excessive (fetal macrosomia).

Assessment of Fetal Well-Being

All pregnant women should receive regular antenatal care throughout their pregnancy, and fetal well-being should be evaluated at every visit. Fetal heart activity should be assessed and the fetal heart rate (FHR) estimated. A low FHR (< 100 bpm) is associated with an increased risk for pregnancy loss, although congenital complete heart block should be excluded. In the latter half of pregnancy, physical examination of the abdomen should be performed to document fetal lie and presentation.

Fetal movements (“quickening”) are typically reported at 18 to 20 weeks’ gestation by nulliparous women and at 16 to 18 weeks’ gestation by parous women; the presence of fetal movements is strongly correlated with fetal health. Although the mother appreciates only 10% to 20% of total fetal movements, such movements are almost always present when she does report them. Factors associated with a diminution in perceived fetal movements include increasing gestational age, smoking, decreased amniotic fluid volume, anterior placentation, and antenatal corticosteroid therapy. Decreased fetal movements may also be a harbinger of an adverse pregnancy event (e.g., stillbirth) that can be averted if detected early. For these reasons, a subjective decrease in perceived fetal movements in the third trimester should prompt an immediate investigation.

Published studies support the value of fetal movement charts (“kick counts”) in the detection and prevention of fetal complications (including stillbirth) in both high- and low-risk populations. The normal fetus exhibits an average of 20 to 50 (range of 0 to 130) gross body movements per hour, with fewer movements during the day and increased activity between 9:00 pm and 1:00 am . Several different schemes have been proposed to determine the baseline fetal activity pattern for an individual fetus after 28 weeks’ gestation and to evaluate activity patterns that may represent fetal compromise. One commonly used scheme (“count-to-10”) instructs the mother to rest quietly on her left side once each day in the evening (between 7:00 pm and 11:00 pm ) and to record the time interval required to feel 10 fetal movements. Most patients with a healthy fetus will feel 10 movements in approximately 20 minutes; 99.5% of women with a healthy fetus feel this amount of activity within 90 minutes. Under this scheme, failure to appreciate 10 fetal movements in 2 hours should prompt immediate fetal assessment. In one large clinical trial, institution of this fetal activity monitoring scheme resulted in a significant increase in hospital visits, labor induction, and cesarean deliveries, but also in a reduction in perinatal mortality from 44.5 to 10.3 per 1000 births. Taken together, these data suggest that daily or twice-daily fetal “kick counts” should be performed after 32 weeks’ gestation in high-risk pregnancies. Currently there is insufficient evidence to recommend this practice in low-risk pregnancies.

Goals of Antepartum Fetal Testing

The goal of antepartum fetal surveillance is the early identification of a fetus at risk for preventable neurologic injury or death. Numerous causes of neonatal cerebral injury exist, including congenital abnormalities, chromosomal abnormalities, intracerebral hemorrhage, hypoxia, infection, drugs, trauma, hypotension, and metabolic derangements (e.g., hypoglycemia, thyroid dysfunction). Antenatal fetal testing cannot reliably predict or detect all of these causes; however, those specifically associated with uteroplacental vascular insufficiency should be identified when possible. Antenatal fetal testing makes the following assumptions: (1) pregnancies may be complicated by progressive fetal asphyxia that can lead to fetal death or permanent neurologic handicap; (2) current antenatal tests can adequately discriminate between asphyxiated and nonasphyxiated fetuses; and (3) detection of asphyxia at an early stage can lead to an intervention that is capable of reducing the likelihood of an adverse perinatal outcome.

Unfortunately, it is not clear whether any of these assumptions are true, and nonreassuring fetal test results may reflect existing but not ongoing neurologic injury. At most, 15% of cases of cerebral palsy are thought to result from antepartum or intrapartum hypoxic-ischemic injury. Despite these limitations, a number of antepartum tests have been developed in an attempt to identify fetuses at risk. These include the nonstress test (NST), biophysical profile (BPP), and contraction stress test (CST). Such tests can be used either individually or in combination. There is no consensus as to which of these modalities is preferred, and no single method has been shown to be superior.

Antepartum Fetal Tests

All antepartum fetal tests should be interpreted in relation to the gestational age, the presence or absence of congenital anomalies, and underlying clinical risk factors. For example, a nonreassuring NST in a pregnancy complicated by severe fetal growth restriction and heavy vaginal bleeding at 32 weeks’ gestation has a much higher predictive value in identifying a fetus at risk for subsequent neurologic injury than an identical tracing in a well-grown fetus at 40 weeks, because of the higher prevalence of this condition in the former situation. It should be remembered that, in many cases, the efficacy of antenatal fetal testing in preventing long-term neurologic injury has not been validated by prospective randomized clinical trials. Indeed, because of ethical and medicolegal concerns, there are no studies of pregnancies at risk that include a nonmonitored control group, and it is highly unlikely that such trials will ever be performed.

Nonstress Test

The fetal NST, also known as fetal cardiotocography, investigates changes in the FHR pattern with time and reflects the maturity of the fetal autonomic nervous system; for this reason, it is less useful in the very preterm fetus (< 28 weeks’ gestation). The NST is noninvasive, simple to perform, inexpensive, and readily available in all obstetric units. However, interpretation of the NST is largely subjective. Although a number of different criteria have been used to evaluate these tracings, most obstetric care providers have used the definitions for FHR interpretation established in 1997, and updated in 2008, by the National Institute of Child Health and Human Development (NICHD) Research Planning Workshop ( Table 6.2 ).

TABLE 6.2

Interpretation of Antepartum Nonstress Test Results

Criterion	Definition
Baseline fetal heart rate (FHR)	Defined as the approximate mean FHR during a 10-min segment and lasting at least 2 min. The normal FHR is defined as 110 to 160 bpm.
Baseline FHR variability	Described as fluctuations in the baseline FHR of ≥ 2 cycles/min. It is quantified visually as the amplitude of peak-to-trough in bpm. Variability is classified as follows: • Absent: amplitude range undetectable • Minimal: amplitude range detectable but ≤ 5 bpm • Moderate: amplitude range 6 to 25 bpm • Marked: amplitude range > 25 bpm The normal baseline FHR variability is defined as moderate variability.
Accelerations	Defined as an abrupt increase in FHR above baseline. • At and after 32 weeks’ gestation, an acceleration is defined as ≥ 15 bpm above baseline for ≥ 15 sec but < 2 min. • Before 32 weeks’ gestation, an acceleration is defined as ≥ 10 bpm above baseline for ≥ 10 sec but < 2 min. A prolonged acceleration is defined as an acceleration lasting ≥ 2 min but < 10 min. If the duration is longer than 10 min, it is referred to as a “change in baseline” and not a prolonged acceleration.
Decelerations	Decelerations are not normal. However, some decelerations are a more serious sign of fetal compromise than others. The following three types of decelerations are recognized: • Early decelerations are characterized by a gradual decrease and return to baseline FHR associated with a uterine contraction. The onset, nadir, and recovery of the deceleration are coincident with the beginning, peak, and ending of the uterine contraction. • Variable decelerations are characterized by an abrupt decrease in the FHR to ≥ 15 bpm below the baseline and lasting for ≥ 15 sec but < 2 min. Abrupt is defined as < 30 sec from baseline to the nadir of the deceleration. When variable decelerations are associated with uterine activity, their onset, depth, and duration commonly vary with successive contractions. • Late decelerations are characterized by a gradual decrease and return to baseline FHR associated with a uterine contraction. Importantly, the deceleration is delayed in timing, with the nadir of the deceleration occurring after the peak of the contraction. Onset, nadir, and recovery of the deceleration occur after the beginning, peak, and ending of the uterine contraction. A prolonged deceleration is defined as a deceleration lasting ≥ 2 min but < 10 min. If the duration is longer than 10 min, it is referred to as a “change in baseline” and not a prolonged deceleration. Recurrent decelerations describe the presence of decelerations with more than 50% of uterine contractions in any 20-min period.

 

Data from the National Institute of Child Health and Human Development Research Planning Workshop. Electronic fetal heart rate monitoring: research guidelines for interpretation. Am J Obstet Gynecol. 1997;177:1385–1390.

By definition, an NST is performed before the onset of labor and does not involve invasive (intrauterine) monitoring. The test is performed by recording the FHR for a period of 20 to 40 minutes; the recording is then evaluated for the presence of periodic changes. The FHR is determined externally with use of Doppler ultrasonography, in which sound waves emitted from the transducer are deflected by movements of the heart and heart valves. The shift in frequency of these deflected waves is detected by a sensor and converted into heart rate. The FHR is printed on a strip-chart recorder running at 3 cm/min. A single mark on the FHR tracing therefore represents the average rate in beats per minute (bpm) of 6 fetal heart beats. The presence or absence of uterine contractions is typically recorded at the same time with an external tonometer. This tonometer records myometrial tone and provides information about the timing and duration of contractions, but it does not measure intrauterine pressure or the intensity of the contractions. Results of the NST are interpreted as reactive or nonreactive. An FHR tracing is designated reactive if there are two or more accelerations that peak, but not necessarily remain, at least 15 bpm for 15 seconds in a 20-minute period ( Fig. 6.3 ). For preterm fetuses (< 32 weeks’ gestation), an FHR tracing is designated as reactive if there are two or more accelerations of at least 10 bpm for 10 seconds. A reactive NST is regarded as evidence of fetal health.

A normal (reactive) fetal heart rate (FHR) tracing. The baseline FHR is normal (between 110 and 160 bpm), there is moderate variability (defined as 6 to 25 bpm from peak to trough), there are no decelerations, and there are two or more accelerations (defined as an increase in FHR of ≥ 15 bpm above baseline lasting at least 15 seconds) in a 20-minute period.

A nonreactive NST does not achieve sufficient accelerations within a 40-minute period; this finding does not necessarily indicate a compromised fetus, as most often it is secondary to a fetal sleep cycle. The interpretation of a nonreactive NST must consider the gestational age, the underlying clinical circumstance, and the results of previous FHR tracings. Only 65% of fetuses have a reactive NST by 28 weeks’ gestation, whereas 95% do so by 32 weeks. However, once a reactive NST has been documented in a given pregnancy, the NST should remain reactive throughout the remainder of the pregnancy. A nonreactive NST at term is associated with poor perinatal outcome in only 20% of cases. The significance of such a result at term depends on the clinical endpoint under investigation. If the clinical endpoint of interest is a 5-minute Apgar score less than 7, a nonreactive NST at term has a sensitivity of 57%, a positive predictive value of 13%, and a negative predictive value of 98% (assuming a prevalence of 4%). If the clinical endpoint is permanent neurologic injury, a nonreactive NST at term has a 99.8% false-positive rate.

Visual interpretation of the FHR tracing involves the following components: (1) baseline FHR, (2) baseline FHR variability, (3) presence of accelerations, (4) presence of periodic or episodic decelerations, and (5) changes of FHR pattern over time. The definitions of each of these variables are summarized in Table 6.2 . The patterns are categorized as baseline, periodic (i.e., associated with uterine contractions), or episodic (i.e., not associated with uterine contractions). Periodic changes are described as abrupt or gradual (defined as onset-to-nadir time < 30 seconds or > 30 seconds, respectively). In contrast to earlier classifications, this classification makes no distinction between short-term and long-term variability, and certain characteristics (e.g., the definition of an acceleration) depend on gestational age.

A normal FHR tracing is defined as having a normal baseline rate (110 to 160 bpm), normal baseline variability (i.e., moderate variability, defined as 6 to 25 bpm from peak to trough), presence of accelerations, and absence of decelerations. FHR accelerations typically occur in response to fetal movement, and usually indicate fetal health and adequate oxygenation. At-risk FHR patterns demonstrate absence of baseline variability, combined with recurrent late or variable decelerations or substantial bradycardia ( Fig. 6.4 ). Intermediate FHR patterns have characteristics between the two extremes of normal and at-risk tracings already described.

An “at-risk” fetal heart rate (FHR) tracing. The baseline FHR is normal (between 110 and 160 bpm), but the following abnormalities can be seen: minimal baseline FHR variability (defined as 0 to 5 bpm from peak to trough), no accelerations, and decelerations that are late in character (start after the peak of the contraction) and repetitive (occur with more than half of the contractions).

Persistent fetal tachycardia (defined as an FHR > 160 bpm) may be associated with fetal hypoxia, maternal fever, chorioamnionitis (intrauterine infection), administration of an anticholinergic or beta-adrenergic receptor agonist, fetal anemia, or tachyarrhythmia (see Table 6.2 ). Persistent fetal bradycardia (FHR < 110 bpm) may be a result of congenital heart block, administration of a beta-adrenergic receptor antagonist, hypoglycemia, or hypothermia; it may also indicate fetal hypoxia. Both tachyarrhythmias and bradyarrhythmias require immediate evaluation.

Baseline FHR variability, perhaps the most important component of the NST, is determined on a beat-to-beat basis by the competing influences of the sympathetic and parasympathetic nervous systems on the fetal sinoatrial node. A variable FHR tracing, characterized by fluctuations that are irregular in both amplitude and frequency, indicates that the autonomic nervous system is functioning and that the fetus has normal acid-base status. Variability is defined as absent, minimal, moderate, or marked ( Fig. 6.5 ). The older terms short-term variability and long-term variability are no longer used. Normal (moderate) variability indicates the absence of cerebral hypoxia. With acute hypoxia, variability may be minimal or marked. Persistent or chronic hypoxia is typically associated with loss of variability. Reduced variability also may be the result of other factors, including maternal drug administration ( Table 6.3 ), fetal arrhythmia, and neurologic abnormality (e.g., anencephaly).

Components of baseline fetal heart rate (FHR) variability. A, Absence of variability. B, Minimal variability (0 to 5 bpm from peak to nadir). C, Moderate variability (6 to 25 bpm from peak to nadir). D, Marked variability (> 25 bpm from peak to nadir).

TABLE 6.3

Drugs That Affect the Fetal Heart Rate Tracing

Effect on the Fetus	Drug
Fetal tachycardia	Atropine
	Epinephrine (adrenaline)
	Beta-adrenergic agonists (ritodrine, terbutaline)
Fetal bradycardia	Antithyroid medications (including propylthiouracil)
	Beta-adrenergic antagonists (e.g., propranolol)
	Intrathecal or epidural analgesia
	Methylergonovine (contraindicated before delivery)
	Oxytocin (if associated with excessive uterine activity)
Sinusoidal fetal heart rate pattern	Systemic opioid analgesia
Diminished variability	Atropine
	Anticonvulsants (but not phenytoin)
	Beta-adrenergic antagonists
	Antenatal corticosteroids (betamethasone, dexamethasone)
	Ethanol
	General anesthesia
	Hypnotics (including diazepam)
	Insulin (if associated with hypoglycemia)
	Magnesium sulfate
	Systemic opioid analgesia
	Promethazine

 

Biophysical Profile

An NST alone may not be sufficient to confirm fetal well-being. In such cases, a biophysical profile (BPP) may be performed. The BPP combines an NST with an ultrasonographic scoring system performed over a 30-minute period. Initially described for testing of the postterm fetus, the BPP has since been validated for use in both term and preterm fetuses, but not during active labor. The five variables described in the original BPP were (1) gross fetal body movements, (2) fetal tone (i.e., flexion and extension of limbs), (3) amniotic fluid volume, (4) fetal breathing movements, and (5) the NST ( Table 6.4 ). More recently, the BPP has been interpreted without the NST.

TABLE 6.4

Characteristics of the Biophysical Profile

Biophysical Variable	Normal Score (Score = 2)	Abnormal Score (Score = 0)
FBM	At least one episode of FBM lasting at least 30 sec	Absence of FBM altogether or no episode of FBM lasting ≥ 30 sec
Gross body movements	At least three discrete body/limb movements in 30 min (episodes of active continuous movements should be regarded as a single movement)	Fewer than three episodes of body/limb movements over a 30-min period
Fetal tone	At least one episode of active extension with return to flexion of fetal limbs or trunk; opening and closing of hand are considered normal tone	Slow extension with return to partial flexion, movement of limb in full extension, or absence of fetal movements
Qualitative AF volume	At least one pocket of AF that measures ≥ 1 cm in two perpendicular planes	No AF pockets or an AF pocket measuring < 1 cm in two perpendicular planes
Reactive nonstress test	At least two episodes of FHR acceleration of ≥ 15 bpm lasting ≥ 15 sec associated with fetal movements over 30 min of observation	Fewer than two episodes of FHR acceleration or accelerations of < 15 bpm over 30 min of observation

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