Antepartum Course

Antepartum Course

Uniform Perinatal Record A consistent method of recordkeeping which is easily understandable from doctor to doctor and location to location is ideal to manage the high-risk patient. In the event of a transfer of care during a pregnancy, or a review of a previous pregnancy, having a coherent, accessible prenatal record helps avoid duplication of tests and helps to expedite diagnostic confirmation and the onset of treatment. Preprinted records such as American College of Obstetricians and Gynecologists (ACOG) forms provide uniform data for each patient and are helpful in diagnosis as well as in management decision making. Prenatal Visits Every prenatal visit is an opportunity to not only screen for problems that may complicate the course of the pregnancy but also to anticipate any problems before they develop. Several factors should be evaluated at each visit. Vital Signs Fever (> 100.4° F), even without other subjective complaints may be due to a wide source of infectious etiologies. Urinary, pulmonary, and hematological sources of the fever should be considered. Signs or symptoms of chorioamnionitis should be assessed, and if chorioamnionitis is suspected, amniocentesis for microscopy and culture should be considered. Depending on clinical correlation, delivery may be necessary. Very high fevers (> 103° F) may trigger preterm labor and may also have an adverse effect on the early development of the fetal central nervous system. Antipyretics may be necessary to lower the temperature. Pulse Maternal tachycardia can be a sign of infection, anemia, or both. Isolated mild tachycardia (> 100 beats per minute [bpm]) should be evaluated and followed up. Moderate to severe tachycardia (> 120 bpm) needs immediate evaluation, including but not limited to a hemogram and an electrocardiogram (ECG). Blood Pressure The normal pattern of maternal blood pressure readings is for a decrease from baseline during the first trimester, reaching its nadir in the second trimester, and slightly rising in the third trimester, although not as high as the baseline levels. Repeated blood pressure readings of 140/90 mm Hg 6 hours apart or a rise of 30 mm Hg systolic pressure or 15 mm Hg diastolic pressure should be considered evidence of pregnancy-induced hypertension. Consideration of the patient's medical history, prepregnancy blood pressure, and gestational age should all be considered in forming a diagnosis and management strategy. Urinalysis At the first prenatal visit, a clean-catch urine culture and sensitivity should be performed. Any growth should be treated with the appropriate antibiotics. At all subsequent visits, urine dipstick testing to screen for protein, glucose, leukocyte esterase, blood, or any combination of markers is useful in identifying patients with a change in their baseline urinary composition. Screening Tests Screening tests are performed at the appropriate time during the pregnancy. FASTER (First and Second Trimester Evaluation of Risk for Aneuploidy) Trial Transvaginal sonography between 10 weeks 3 days and 13 weeks 6 days to visualize and measure nuchal translucency, along with serum measurements of pregnancy associated plasma protein (PAPP-A) and free -human chorionic gonadotropin (hCG) is currently being studied in several institutions throughout the United States as a screen for Down syndrome, as well as other aneuploidies and malformations. Maternal Serum Analyte Testing Frequently known as the "triple screen," this test includes maternal serum alpha-fetoprotein (msAFP), -hCG, and estriol. In some institutions, only the msAFP is used, while in other institutions a fourth test, inhibin, is included, making it a "quad test." The usefulness of this screen is its ability to identify pregnancies at an increased risk for open neural tube defects, as well as for certain chromosomal abnormalities, especially trisomy 21 (75% sensitivity for Down syndrome detection). This test is effective at 15–19 weeks' gestation and can therefore identify an at-risk pregnancy in time to pursue more definitive diagnosis, if desired. It is important to note, however, that the triple screen is not a definitive test and that many positive screens have yielded normal fetuses and many abnormal fetuses have had normal screens. Diabetes Screen Routine screening consists of performing a glucose challenge test between 24 and 28 weeks. The test consists of a 50-g oral glucose load with a plasma glucose level drawn exactly 1 hour after. If the value is over 140 mg/dL, a more specific glucose tolerance test (GTT) should be performed. The GTT involves obtaining a fasting plasma glucose level, giving a 100-g oral glucose load, then drawing plasma levels at 1 hour, 2 hours, and 3 hours after the glucose load. A test is considered positive for gestational diabetes if two out of the four values are elevated. Isoimmunization A patient who is Rh-negative with a pregnancy fathered by an Rh-positive man should be screened for antibodies at the first prenatal visit and again at 24–28 weeks. If there continues to be no antibodies, Rhogam should be administered at 28 weeks to prevent sensitization of the mother during the last trimester and delivery. In the event of a previously isoimmunized patient, the typing and screening performed at the initial visit would detect antibodies, which are reported as a numerical titer. These titers should be followed every 4 weeks to assess for worsening isoimmunization. In the presence of worsening titers, follow-up with amniocentesis may be appropriate. Peak systolic velocity of the fetal middle cerebral artery as determined by sonographic Doppler evaluation has been demonstrated to correlate with degree of fetal anemia, allowing for noninterventional diagnosis and management of fetal isoimmunization; however, the definitive treatment is intrauterine fetal transfusion. Beta Hemolytic Streptococcus This is also known as the group B Streptococcus (GBS) test, and between 10% and 30% of pregnant women are colonized with GBS in the vaginal or rectal areas. Whereas they are usually asymptomatic colonizations, perinatal transmission can result in a severe and potentially fatal neonatal infection. Any documented GBS bacteriuria needs to be treated at the time of diagnosis, as well as intrapartum. Intrapartum antibiotic prophylaxis has been shown to decrease the risk of perinatal GBS transmission. There are two approaches to screening: Screen patients at 35–37 weeks' gestation and treat positive cultures with intrapartum antibiotics, or treat patients based on risk factors with intrapartum antibiotic prophylaxis. Fetal Assessment Comprehensive fetal assessment begins in the first trimester with nuchal translucency and continues throughout the pregnancy into labor and delivery. Conceptually, antepartum testing in pregnancies at risk falls into one of two categories: assessment of prenatal diagnosis and assessment of fetal well-being. Assessment of Prenatal Diagnosis Performed during all trimesters, the techniques used are diverse, and the information obtained varies according to the quality of imaging, depth of investigation, and gestational age of pregnancy. Ultrasound Ultrasound has had a continuous evolution over the last 20 years, with better equipment being produced each year. Real-time sonography allows a 2-D image to demonstrate fetal anatomy, as well as characteristics such as fetal weight, movement, volume of amniotic fluid, and structural anomalies such as myomas or placenta previa which may affect the pregnancy. 3-D sonography allows volume to be ascertained, creating a three-dimensional appearing image on the 2-D screen, which assists in identifying certain anatomical anomalies. Most recently, 4-D machines have been developed, which produce a 3-D image in real time. As the machines become more technically advanced and the computers that run them become faster, the images obtained will continue to improve and push the boundaries of sonographic prenatal diagnosis. Diagnostic ultrasonography is widely used in the assessment of the pregnancy and the fetus. It is not, however, the standard of care, nor is it recommended by ACOG for every pregnancy. The indications for ultrasonography are multiple and diverse, and the type and timing of the examination varies depending on the information being sought. A basic ultrasound examination should provide such information as fetal number, presentation, documentation of fetal viability, placental location, and assessment of gestational age. A limited ultrasound examination is a goal-directed search for a suspected problem or finding. A limited ultrasound may be used for guidance during procedures such as amniocentesis or external cephalic version, assessment of fetal well being, or documentation of presentation or placental location intrapartum. A comprehensive ultrasound examination provides information on fetal anatomy, growth, anomalies, and physiologic complications. Ultrasound evaluation of fetal anatomy may detect some major structural anomalies. Gross malformations such as anencephaly and hydrocephaly are more commonly diagnosed and rarely missed; however, more subtle anomalies such as facial clefts, diaphragmatic hernias, and neural tube defects are more commonly reported to have been missed by ultrasound. The basic fetal anatomy survey should include visualization of the cerebral ventricles, four-chamber view of the heart, and examination of the spine, stomach, urinary bladder, umbilical cord insertion site, and renal region. Any indication of an anomaly should be followed by a more comprehensive sonogram. Typically, the fetal anatomic survey is performed at 17–20 weeks; however, there is controversy surrounding the potential benefits of an earlier sonogram at 14–16 weeks using the transvaginal probe. The earlier scan allows earlier detection of anomalies that are almost always present by the second trimester, as well as allowing greater detailed viewing of the fetal anatomy by using the higher-resolution vaginal transducers. Aneuploidy Screening Multiple sonographic markers for aneuploidy have been identified. The presence of single or multiple markers adjusts the patient's age-related risk of aneuploidy based on the particular markers present. Such sonographic findings include, but are not limited to:     Echogenic intracardiac focus     Choroid plexus cysts     Pyelectasis     Echogenic bowel     Short femur     Hypomineralization of the fifth digit of the fetal hand Amniocentesis Amniocentesis is frequently performed under the guidance of ultrasonography. A needle is inserted transcutaneously through the abdominal wall into the amniotic cavity, and fluid is removed. There are many uses for this amniotic fluid, including cytology for detection of infection, alpha-fetoprotein evaluation for neural tube defect assessment, assessment of fetal lung maturity (which will be discussed later in the chapter), and the most common indication of cytogenetic analysis. In this case, amniocentesis is often performed between 15 and 20 weeks' gestation and fetal cells from the amniotic fluid are obtained. Risks associated with the procedure are considered to be very low, with the risk of abortion as a result of amniocentesis considered to be between 1 in 200 to 1 in 450 amniocenteses. Chorionic Villus Sampling Chorionic villus sampling (CVS) is an alternative to amniocentesis. It is performed between 10 and 12 weeks' gestation, and can be performed either transcervically or transabdominally. CVS is also performed under sonographic guidance, with the passing of a sterile catheter or needle into the placental site. Chorionic villi are aspirated and undergo cytogenetic analysis. The benefit of CVS over amniocentesis is its availability earlier in pregnancy; however, the rate of abortion is higher—as high as 1%. One disadvantage of CVS is that unlike amniocentesis, it does not allow diagnosis of neural tube defects. Fetal Blood Sampling Also referred to as cordocentesis or percutaneous umbilical blood sampling (PUBS), this is an option for chromosomal or metabolic analysis of the fetus. Benefits of the procedure include a rapid result turnaround rate and the ability to perform the procedure in the second and third trimester. Intravascular access to the fetus is useful for the assessment and treatment of certain fetal conditions such as Rh sensitization and alloimmune thrombocytopenia. There is a higher risk of fetal death, however, when compared to the other methods. Fetal loss rates are approximately 2%, but can vary depending on the fetal condition involved. Assessment of Fetal Well-Being Fetal Monitoring Techniques Assessment of fetal status can be performed using a wide variety of techniques. External Fetal Monitoring The external measurement of the fetal heart rate is done by using a continuous beam of ultrasound waves focused on the fetal heart. This ultrasound monitor utilizes Doppler effects to sample the frequency of moving fetal heart valves and the atrial and the ventricular systole. The complex received signal wave is then peak detected and entered into the heart rate monitor. The computer averages several consecutive frequencies, which helps minimize artifact, before the signal is displayed and printed. This process of averaging is called autocorrelation, and produces a fetal heart rate pattern which closely resembles that derived from a fetal ECG, although there is more baseline variability inherent in this method. Internal Fetal Monitoring The internal measurement of the fetal heart rate is an invasive procedure, utilizing an electrode attached to the fetal scalp. A bipolar spiral electrode is placed transcervically and penetrates the fetal scalp. A reference electrode is placed on the maternal thigh to eliminate electrical interference. The fetal ECG is detected, and the R wave is the signal used for peak detection and for counting. This signal is very clear, and allows accurate beat-to-beat and baseline variability to be measured. Artifact is kept to a minimum, and there is little need for autocorrelation. Sonographic Fetal Monitoring There have been reports of a number of sonographically related surveillance techniques for fetal status published in the literature. Such testing techniques as biophysical profile and Doppler velocimetry have been extensively studied and widely used for antepartum evaluation. Doppler velocimetry is a noninvasive technique based on vascular impedance. Most often, the umbilical artery is utilized for this purpose. Both the peak values as well as the actual waveform can be utilized to identify abnormally growing fetuses, or fetuses at risk of cardiac failure or other adverse outcome. Most of the benefit is seen in growth-restricted pregnancies, and use for generalized surveillance is not recommended. Biophysical profile consists of fetal heart rate evaluation combined with sonographically assessed parameters of fetal well being, including fetal breathing movements, fine motor movement, gross fetal tone, and amniotic fluid volume. Fetal Heart Rate Interpretation Antepartum Fetal Surveillance In determining which patients should have antepartum fetal surveillance, a major factor to consider is the lack of evidence that any routine surveillance method results in a decreased risk of fetal death. Therefore, we generally begin monitoring in pregnancies in which the risks of fetal demise are known to be increased. These can include maternal conditions such as antiphospholipid syndrome, lupus, diabetes, or other maternal medical problems. They can also include pregnancy-related conditions such as preeclampsia, IUGR, multiple gestation, poor obstetrical history, or postterm pregnancy. Antepartum surveillance should include a nonstress test (NST) as a minimum. The addition of sonographic monitoring is common, most often as some variant of the biophysical profile. The criteria for the NST are: baseline between 120 and 160 bpm, the presence of periodic accelerations (ie, two accelerations in 20 minutes) of fetal heart rate of 15 bpm over baseline for 15 seconds, the absence of decelerations of the fetal heart rate, and the subjective assessment of variability of the fetal heart rate. In the case of a nonreassuring NST, further evaluation or delivery depend on the clinical context. In a patient at term, delivery is warranted. Near term, determination of fetal lung maturity can be considered. Remote from term poses a more challenging dilemma to the clinician. If resuscitative efforts are not successful in restoring reactivity to the NST, ancillary tests or testing techniques may prove useful in avoiding a premature iatrogenic delivery for nonreassuring fetal heart rate patterns, since the false-positive rate may be as high as 50–60%. Ancillary Tests Vibroacoustic Stimulation An auditory source, often an artificial larynx, is placed on the maternal abdomen. A short burst of sound is delivered to the fetus. This has proven successful in shortening the duration needed for the test to show reactivity, without compromising the predictive value of the absence of acidosis with a reactive NST. Fetal Scalp Stimulation The presence of an acceleration after a vaginal exam where the examiner stimulates the fetal vertex with the examining finger confirms the absence of acidosis (pH > 7.2). Oxytocin Challenge Test This may be used to elicit a confirmatory abnormal fetal heart rate response, with one report showing a better correlation with adverse outcome than the NST alone. Other studies, however, have demonstrated no improvement in predicting morbidity over an NST. This is performed by intravenous infusion of dilute oxytocin until three contractions occur in 10 minutes. A positive test indicates decreased fetal reserve, with a 20–40% incidence of abnormal fetal heart rate (FHR) patterns in labor. A positive test is the presence of a late deceleration after each of the three contractions, a negative test shows no decelerations, and anything else is equivocal. Repetitive variable decelerations are termed "suspicious" and are associated with abnormal FHR patterns in labor, particularly in postterm gestations. Fetal Maturity Tests Indications for assessing fetal lung maturity—The American College of Obstetricians and Gynecologists has recommended that fetal pulmonary maturity should be confirmed before elective delivery at less than 39 weeks' gestation unless fetal maturity can be inferred from any of these criteria: Fetal heart tones have been documented for 20 weeks by nonelectronic fetoscope or for 30 weeks by Doppler; and 36 weeks have elapsed since a serum or urine hCG-based pregnancy test was reported to be positive. Lecithin:Sphingomyelin Ratio The lecithin:sphingomyelin (L:S) ratio for assessment of fetal pulmonary maturity was first introduced by Gluck and colleagues in 1971. The test depends upon outward flow of pulmonary secretions from the lungs into the amniotic fluid, thereby changing the phospholipid composition of the latter and permitting measurement of the ratio of lecithin to sphingomyelin in a sample of amniotic fluid. The concentrations of these two substances are approximately equal until 32–33 weeks of gestation, at which time the concentration of lecithin begins to increase significantly while the sphingomyelin concentration remains about the same. The measurement of sphingomyelin serves as a constant comparison for control of the relative increases in lecithin because the volume of amniotic fluid cannot be accurately measured clinically. Determination of the L:S ratio involves thin-layer chromatography after organic solvent extraction. It is a difficult test to perform and interpret; care at each step of sample handling is critical for consistent results. The sample should be kept on ice or refrigerated if transport to a laboratory is required. Improper storage conditions can change the L:S ratio since amniotic fluid contains enzymes that can be affected by temperature. The amniotic fluid samples must be mixed well. The presence of blood or meconium can interfere with test interpretation. Bloody samples give false information due to the presence of sphingomyelin in blood and decreased extraction of lecithin by cold acetone techniques in the presence of red blood cells. Therefore, if blood or other particulate matter is present in the amniotic fluid sample, a low-speed, short centrifugation can be used to remove the cellular component. Interpretation of the results should be carried out with consideration of the individual clinical circumstances. For example, some physicians require a higher L:S ratio for confirmation of fetal pulmonary maturity in pregnancies complicated by isoimmunization or diabetes mellitus. A threshold value for prediction of lung maturity should be calculated in individual centers by correlation with clinical outcome, because the variation within and between laboratories can be considerable. Empirically, the risk of respiratory distress syndrome (RDS) is exceedingly low when the L:S ratio is greater than 2.0. Phosphatidylglycerol Phosphatidylglycerol (PG) is a minor constituent of surfactant. It begins to increase appreciably in amniotic fluid several weeks after the rise in lecithin. Its presence is more indicative of fetal lung maturity as PG enhances the spread of phospholipids on the alveoli; thus, its presence indicates a more advanced state of fetal lung development and function. PG determination is not generally affected by blood, meconium, or other contaminants; its ability to predict pulmonary maturity is the same whether or not contam-ination is present. This is an advantage for assessing fetal lung maturity status since these substances are commonly found in amniotic fluid. PG testing is performed by thin-layer chromatography (as for the L:S measurement), so it may be determined alone or in conjunction with L:S testing. It can be reported qualitatively as positive or negative, where positive represents an exceedingly low risk of RDS, or in a quantitative fashion, in which a value 0.3 is associated with a minimal rate of respiratory distress. Foam Stability Index The foam stability index (FSI) is a rapid predictor of fetal lung maturity and is based upon the ability of surfactant to generate stable foam in the presence of ethanol. Ethanol is added to a sample of amniotic fluid to eliminate the effects of nonsurfactant factors on foam formation. The mixture is shaken and will demonstrate generation of a stable ring of foam if surfactant is present in the amniotic fluid. The FSI is calculated by utilizing serial dilutions of ethanol to quantitate the amount of surfactant present. Amniotic fluid samples should not be collected in silicone tubes when this test is planned, as the silicone will produce "false foam." The discriminating value indicative of lung maturity is usually set at 47. A positive result virtually excludes the risk of RDS; however, a negative test often occurs in the presence of mature lungs. The presence of blood or meconium interferes with results of the FSI. Fluorescence Polarization The fluorescence polarization test uses polarized light to quantitate the competitive binding of a probe to both albumin and surfactant in amniotic fluid; thus, it is a true direct measurement of surfactant concentration. It reflects the ratio of surfactant to albumin and is measured by an automatic analyzer, such as the TDx-FLM. An elevated ratio has been correlated with the presence of fetal lung maturity; the threshold for maturity is 55 mg of surfactant per gram of albumin. Evaluation of the accuracy of TDx measurements has also been studied, specifically in diabetic patients. Despite initial evidence that higher cutoffs were required for diabetics, it is currently believed that the same cutoff for lung maturity can be used for both nondiabetic and diabetic patients. The accuracy of this test compares favorably with the well-established L:S and PG tests. Blood and meconium contamination interfere with interpretation, although the degree or direction of the interference is unclear. There is insufficient evidence regarding the accuracy of this test for determination of fetal lung maturity in vaginally-collected specimens. A disadvantage to the TDx-FLM method is the large quantification scale. Values greater than 55 are regarded as mature; however, values of 35–55 are considered borderline. In addition, there is controversy as to whether gestational age should be used in interpreting the TDx for determining the likelihood of RDS. In one report, higher threshold values were needed at earlier gestational ages to determine lung maturity and lower thresholds were required at later gestational ages. Table 13–4 summarizes the value of these tests of fetal maturity and gives their relative costs. Intrapartum Fetal Surveillance Assessment of the fetus in labor is a challenging task. Certain techniques that were useful in the antepartum period are no longer accurate, and certain new techniques have become available. With the presence of contractions, fetal heart rate monitoring is no longer a nonstress test. Fetal heart rate assessment is still the initial test of choice. Continuous fetal monitoring and intermittent auscultation have been extensively reviewed, and the evidence does not support one over the other for routine obstetric care. Several reports suggest that continuous monitoring results in higher operative delivery rates without an associated neonatal benefit. For the present, the controversy over routine FHR monitoring remains, but the clinical practice is nearly universal for continuous electronic monitoring of the FHR in hospitals and many birthing centers. In the intrapartum period, access to the fetus allows for further evaluation in the face of a nonreassuring FHR tracing. Direct measurement of the physiologic status of the fetus is possible after adequate cervical dilation and rupture of the membranes. Ancillary Tests Fetal Scalp Blood Sampling Capillary blood collected from the fetal scalp typically has a pH lower than arterial blood. A pH of 7.20 was initially believed to be the critical value to identify serious fetal stress and an increase in the incidence of low Apgar scores. However, there is much debate over the accuracy of scalp pH in predicting fetal distress with subsequent neurologic sequelae. Continuous scalp pH during labor was highly successful in defining abnormal FHR patterns associated with acidosis, although the advanced technical skill and expense prohibited widespread use. In fact, despite the correlation with FHR, fetal scalp pH is no longer used in many institutions. The only proven benefits reported for scalp pH testing were demonstration of adverse neurologic outcome with pH < 7.1, and fewer cesarean sections for fetal distress. Fetal Lactate Levels Collected in the same fashion as scalp pH, lactate levels demonstrated a higher predictive value than pH as markers of neurologic disability. Fetal Pulse Oximetry This has been studied over the past 10 years. Controversy exists over its potential clinical value. There is debate about its accuracy in correlating with acidemia. Studies have demonstrated no benefit in relation to FHR patterns, or in detecting neurologically-compromised fetuses. A recent report demonstrating a reduction in the rate of cesarean section for a diagnosis of distress, without an actual decrease in the incidence of cesareans compared with the control group, raised questions about the usefulness of the test, since it was hoped that it could reduce the cesarean section rate in a manner similar to scalp pH and lactate assays. Clearly, more studies need to be initiated to demonstrate a clear benefit to this test. Fetal Heart Rate Patterns Reassuring Fetal Heart Rate Patterns Slight deviations from the normal baseline of 120–160 bpm and some periodic changes are innocuous in the continuum of the fetal heart rate pattern. Early decelerations and bradycardia of 100–119 bpm are believed to be vagally mediated due to fetal head compression, and are not associated with fetal acidosis or poor neonatal outcome. Certain cardiac arrhythmias also pose no threat to the fetus while the fetal heart rate pattern deviates from what is considered "normal." In fact, the majority of fetal arrhythmias are benign and spontaneously convert to normal sinus rhythm by 24 hours postpartum. Persistent tachyarrythmias are well tolerated, but may proceed to fetal hydrops if present for many hours to days. Persistent bradyarrhythmias are often associated with fetal heart disease, but are seldom associated with hypoxia or acidosis in fetal life or labor. Accelerations and variable decelerations of variable shape and timing are indicative of a normal autonomic nervous system. Nonreassuring Fetal Heart Rate Patterns This category is of more concern to the clinician, and while there is still evidence that the fetus is not acidotic, continuation or worsening of the clinical situation may result in fetal distress. Late deceleration is a smooth fall in the fetal heart rate beginning after the contraction has started, and ending after the contraction has ended. They are associated with a fall in fetal pH and a potential for perinatal morbidity and mortality. Another nonreassuring pattern is the sinusoidal heart rate. It is best defined as a pattern of regular variability resembling a sine wave with a fixed period of 3–5 cycles per minute and an amplitude of 5–40 bpm. The mechanism for the sinusoidal pattern is believed to be a response to moderate fetal hypoxemia, including secondary to fetal anemia. It was previously thought to carry a high perinatal mortality. However, follow-up with serial scalp pH has been successfully performed with no adverse outcome. The significance of sinusoidal heart rate patterns depends on the clinical setting. Variable decelerations may be divided into categories, with the deciding characteristic being the onset and the timing of the return to baseline. If a variable deceleration, no matter how deep, does not have a late component, then the pattern is benign and at most is mild cord compression not associated with acidosis or low Apgar scores. When there is a late recovery, the fetal pH falls progressively during the period of deceleration. Fetal Distress Patterns Considerable confusion surrounds the diagnosis of fetal distress. Fetal distress should be defined operationally as a pathological condition of the fetus that is likely to cause fetal or neonatal death or damage to the newborn if left uncorrected for a period of greater than 1 hour. It is often, but not always, associated with fetal acidemia and hypoxemia. These metabolic changes are highly correlated with a decompensated fetal homeostasis, but not necessarily with all nonreassuring FHR patterns. There are numerous causes and multiple factors associated with fetal distress; however, only a few fetal heart rate patterns are associated with true fetal distress, including: a. Undulating baseline—Alternating tachycardia and bradycardia with wide swings, often with reduced variability in between. b. Severe bradycardia—Fetal heart rate below 100 bpm for a prolonged period of time of at least 10 minutes. c. Tachycardia with diminished variability unrelated to drugs d. Tachycardia associated with additional nonreassuring periodic patterns such as late decelerations or variable decelerations with late recovery—With careful interpretation, FHR patterns can be a useful screening test for fetal acidemia and hypoxemia. The monitoring and interpretation of the fetal heart rate is ideally used as a screening tool. The presence of a reassuring FHR pattern is just that, reassuring that there is no fetal acidemia at that time. The absence of a reassuring tracing is not necessarily problematic, and ancillary testing can be performed to eliminate false positives. However, it must be remembered that a given segment of FHR monitoring is a single point in time. Pregnancy and labor are ongoing dynamic states. Maternal and fetal conditions and the processes of gestation, especially labor, are stresses which challenge fetal homeostasis. Fetal stress may be manifested in the FHR pattern, while the fetus remains compensated. The clinician must discriminate between stress and distress, using interpretation and ancillary testing. All monitoring techniques are to be ultimately used as supplements to clinical judgment, to obtain the best outcome of pregnancy.