gynecology and obstetrics
Management of Normal Labor
Fetal Monitoring
Fetal status must be monitored during labor. The main parameters are baseline fetal heart rate (HR) and fetal HR variability, particularly how they change in response to uterine contractions and fetal movement. Because interpretation of fetal HR can be subjective, certain parameters have been defined (see table Fetal Monitoring Definitions ). Several patterns are recognized; they are classified into 3 tiers (categories [ Fetal monitoring reference ]), which usually correlate with the acid–base status of the fetus: Category I: Normal Category II: Indeterminate Category III: Abnormal Anormal patternstrongly predicts normal fetal acid-base status at the time of observation. This pattern has all of the following characteristics: HR 110 to 160 beats/minute at baseline Moderate HR variability (by 6 to 25 beats) at baseline and with movement or contractions No late or variable decelerations during contractions Early decelerations and age-appropriate accelerations may be present or absent in a normal pattern. Anindeterminate patternis any pattern not clearly categorized as normal or abnormal. Many patterns qualify as indeterminate. Whether the fetus is acidotic cannot be determined from the pattern. Indeterminate patterns require close fetal monitoring so that any deterioration can be recognized as soon as possible. Anabnormal patternusually indicates fetal metabolic acidosis at the time of observation. This pattern is characterized by one of the following: Absent baseline HR variability plus recurrent late decelerations Absent baseline HR variability plus recurrent variable decelerations Absent baseline HR variability plus bradycardia (HR < 110 beats/minute without variability or < 100 beats/minute) Sinusoidal pattern (fixed variability of about 5 to 40 beats/minute at about 3 to 5 cycles/minute, resembling a sine wave) Abnormal patterns require prompt actions to correct them (eg, supplemental oxygen, repositioning, treatment of maternal hypotension, discontinuation ofoxytocin) or preparation for an expedited delivery. Patterns reflect fetal status at a particular point in time; patterns can and do change. Monitoring can be manual and intermittent, using a fetoscope for auscultation of fetal HR. However, in the US, electronic fetal HR monitoring (external or internal) has become standard of care for high-risk pregnancies, and many clinicians use it for all pregnancies. The value of routine use of electronic monitoring in low-risk deliveries is often debated. Electronic fetal monitoring has not been shown to reduce overall mortality rates in large clinical trials and has been shown to increase rate of cesarean delivery, probably because many apparent abnormalities are false positives. Thus, the rate of cesarean delivery is higher among women monitored electronically than among those monitored by auscultation. Fetal pulse oximetryhas been studied as a way to confirm abnormal or equivocal results of electronic monitoring; status of fetal oxygenation may help determine whether cesarean delivery is needed. Fetal ST-segment and T-wave analysis in labor (STAN)can be used to check the fetal ECG for ST-segment elevation or depression; either finding presumably indicates fetal hypoxemia and has a high sensitivity and specificity for fetal acidosis. For STAN, an electrode must be attached to the fetal scalp; then changes in the T wave and ST segment of the fetal ECG are automatically identified and analyzed. If manual auscultation of fetal HR is used, it must be done throughout labor according to specific guidelines, and one-on-one nursing care is needed. For low-risk pregnancies with normal labor, fetal HR must be checked after each contraction or at least every 30 minutes during the 1st stage of labor and every 15 minutes during the 2nd stage. For high-risk pregnancies, fetal HR must be checked every 15 minutes during the 1st stage and every 3 to 5 minutes during the 2nd stage. Listening for at least 1 to 2 minutes beginning at a contraction’s peak is recommended to check for late deceleration. Periodic auscultation has a lower false-positive rate for abnormalities and incidence of intervention than continuous electronic monitoring, and it provides opportunities for more personal contact with women during labor. However, following the standard guidelines for auscultation is often difficult and may not be cost-effective. Also, unless done accurately, auscultation may not detect abnormalities. Electronic fetal HR monitoring may be External:Devices are applied to the maternal abdomen to record fetal heart sounds and uterine contractions. Internal:Amniotic membranes must be ruptured. Then, leads are inserted through the cervix; an electrode is attached to the fetal scalp to monitor HR, and a catheter is placed in the uterine cavity to measure intrauterine pressure. Usually, external and internal monitoring are similarly reliable. External devices are used for women in normal labor; internal methods are used when external monitoring does not supply enough information about fetal well-being or uterine contraction intensity (eg, if the external device is not functioning correctly). Anonstress testrecords fetal heart rate and uterine contractions using external electronic monitors and correlates the HR with fetal movements (reported by the mother); it is called nonstress because no stressors are applied to the fetus during the test, although sounds (eg, bell, acoustic stimulator) may be used to wake the fetus. HR is expected to increase when the fetus is moving and at other intervals. The nonstress test is typically done for 20 minutes (occasionally for 40 minutes). Results are considered reactive (reassuring) if there are 2 accelerations of 15 beats/minute over 20 minutes. Absence of accelerations is considered nonreactive (nonreassuring). Presence of late decelerations suggests hypoxemia, potential for fetal acidosis, and the need for intervention. is usually done after a nonreassuring nonstress test. The biophysical profile adds ultrasonographic assessment of amniotic fluid volume and sometimes assessment of fetal movement, tone, breathing, and HR, to the nonstress test. A nonstress test and biophysical profile are frequently used to monitor complicated or Overview of High-Risk Pregnancy (eg, complicated by maternal diabetes or hypertension or by stillbirth or fetal growth restriction in a previous pregnancy). Contraction stress testing(oxytocinchallenge test) is now rarely done. In this test, fetal movements and HR are monitored (typically externally) during contractions induced byoxytocin. When done, contraction stress testing must be done in a hospital. If a problem (eg, fetal HR decelerations, lack of normal HR variability) is detected during labor, intrauterine fetal resuscitation is tried; women may be given oxygen by a tight nonrebreather face mask or rapid IV fluid infusion or may be positioned laterally. If fetal heart pattern does not improve in a reasonable period and delivery is not imminent, urgent delivery by cesarean is needed. 1.Macones GA, Hankins GD, Spong CY, et al: The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: Update on definitions, interpretation, and research guidelines.J Obstet Gynecol Neonatal Nurs37 (5):510–515, 2008. doi: 10.1111/j.1552-6909.2008.00284.x 