Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The World Health Organization (WHO) defines normal birth as follows:
The birth is spontaneous in onset and low risk at the start of labor and remains so throughout labor and delivery.
The infant is born spontaneously in the vertex position between 37 and 42 weeks of pregnancy.
After birth, mother and infant are in good condition (1 General reference Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ).
The stimulus for labor is unknown, but digitally manipulating or mechanically stretching the cervix during examination enhances uterine contractile activity, most likely by stimulating release of oxytocin by the posterior pituitary gland.
Normal labor usually begins within 2 weeks (before or after) the estimated delivery date. In a first pregnancy, labor usually lasts 12 to 18 hours on average; subsequent labors are often shorter, averaging 6 to 8 hours.
Management of complications during labor requires additional measures (eg, induction of labor Induction of Labor Induction of labor is stimulation of uterine contractions before spontaneous labor to achieve vaginal delivery. Induction of labor can be Medically indicated (eg, for preeclampsia or fetal compromise)... read more , forceps or a vacuum extractor Operative Vaginal Delivery Operative vaginal delivery involves application of forceps or a vacuum extractor to the fetal head to assist during the 2nd stage of labor and facilitate delivery. Indications for forceps delivery... read more , cesarean delivery Cesarean Delivery Cesarean delivery is surgical delivery by incision into the uterus. Up to 30% of deliveries in the US are cesarean. The rate of cesarean delivery fluctuates. It has recently increased, partly... read more ).
(See also Abnormalities and Complications of Labor and Delivery Introduction to Abnormalities and Complications of Labor and Delivery Abnormalities and complications of labor and delivery should be diagnosed and managed as early as possible. Most of the following complications are evident before onset of labor: Multifetal... read more .)
Beginning of labor
Rupture of the chorioamniotic membranes or bloody show is diagnostic for onset of labor.
Bloody show (a small amount of blood with mucous discharge from the cervix) may precede onset of labor by as much as 72 hours. Bloody show can be differentiated from abnormal 3rd-trimester vaginal bleeding Vaginal Bleeding During Late Pregnancy Bleeding during late pregnancy (≥ 20 weeks gestation, but before birth) occurs in 3 to 4% of pregnancies. It should be evaluated promptly, because it may be associated with complications that... read more because the amount is small, bloody show is typically mixed with mucus, and the pain due to abruptio placentae Placental Abruption (Abruptio Placentae) Placental abruption (abruptio placentae) is premature separation of the placenta from the uterus, usually after 20 weeks gestation. It can be an obstetric emergency. Manifestations may include... read more (premature separation) is absent. In most pregnant women, previous routine ultrasonography has been done and ruled out placenta previa Placenta Previa Placenta previa is implantation of the placenta over or near the internal os of the cervix. It typically manifests as painless vaginal bleeding after 20 weeks gestation; the source of bleeding... read more . However, if ultrasonography has not ruled out placenta previa and vaginal bleeding occurs, placenta previa is assumed to be present until it is ruled out. In such cases, digital vaginal examination is contraindicated, and ultrasonography is done as soon as possible to determine the location of the placenta and rule out abruptio placentae.
Labor begins with irregular uterine contractions of varying intensity; they apparently soften (ripen) the cervix, which begins to efface and dilate. As labor progresses, contractions increase in duration, intensity, and frequency.
Stages of labor
There are 3 stages of labor.
The 1st stage—from onset of labor to full dilation of the cervix (about 10 cm)—has 2 phases, latent and active.
During the latent phase, irregular contractions become progressively coordinated, discomfort is minimal, and the cervix effaces and dilates to 4 cm. The latent phase is difficult to time precisely, and duration varies, averaging 8 hours in nulliparas and 5 hours in multiparas; duration is considered abnormal if it lasts > 20 hours in nulliparas or > 12 hours in multiparas.
During the active phase, the cervix becomes fully dilated, and the presenting part descends well into the midpelvis. On average, the active phase lasts 5 to 7 hours in nulliparas and 2 to 4 hours in multiparas. Traditionally, the cervix was expected to dilate about 1.2 cm/hour in nulliparas and 1.5 cm/hour in multiparas. However, recent data suggest that slower progression of cervical dilation from 4 to 6 cm may be normal (1 Analgesia references Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ). Pelvic examinations are done every 2 to 3 hours to evaluate labor progress. Lack of progress in dilation and descent of the presenting part may indicate dystocia (fetopelvic disproportion).
Standing and walking shorten the first stage of labor by > 1 hour and reduce the rate of cesarean delivery (1 Stages of labor references Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ).
If the membranes have not spontaneously ruptured, some clinicians use amniotomy (artificial rupture of membranes) routinely during the active phase. As a result, labor may progress more rapidly, and meconium-stained amniotic fluid may be detected earlier. Amniotomy during this stage may be necessary for specific indications, such as facilitating internal fetal monitoring to confirm fetal well-being. Amniotomy should be avoided in women with HIV infection or hepatitis B or C, so that the fetus is not exposed to these organisms.
During the 1st stage of labor, maternal heart rate and blood pressure and fetal heart rate should be checked continuously by electronic monitoring or intermittently by auscultation, usually with a portable Doppler ultrasound device (see fetal monitoring Fetal Monitoring Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ). Women may begin to feel the urge to bear down as the presenting part descends into the pelvis. However, they should be discouraged from bearing down until the cervix is fully dilated so that they do not tear the cervix or waste energy.
The 2nd stage is the time from full cervical dilation to delivery of the fetus. On average, it lasts 2 hours in nulliparas (median 50 minutes) and 1 hour in multiparas (median 20 minutes). It may last another hour or more if conduction (epidural) analgesia or intense opioid sedation is used. For spontaneous delivery, women must supplement uterine contractions by expulsively bearing down. In the 2nd stage, women should be attended constantly, and fetal heart sounds should be checked continuously or after every contraction. Contractions may be monitored by palpation or electronically.
During the 2nd stage of labor, perineal massage with lubricants and warm compresses may soften and stretch the perineum and thus reduce the rate of 3rd- and 4th-degree perineal tears (2 Stages of labor references Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ). These techniques are widely used by midwives and birth attendants. Precautions should be taken to reduce risk of infection with perineal massage.
During the 2nd stage (in contrast to the 1st stage), the mother's position does not affect duration or mode of delivery or maternal or neonatal outcome in deliveries without epidural anesthesia (3 Stages of labor references Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ). Also, the pushing technique (spontaneous versus directed and delayed versus immediate) does not affect the mode of delivery or maternal or neonatal outcome. Use of epidural anesthesia delays pushing and may lengthen the 2nd stage by an hour (4 Stages of labor references Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ).
The 3rd stage of labor begins after delivery of the infant and ends with delivery of the placenta. This stage usually lasts only a few minutes but may last up to 30 minutes.
Labor, also called parturition, describes the hard work of delivering a baby! It specifically refers to the process which starts with uterine contractions which cause cervical changes which allow the fetus to be delivered vaginally, and ends with delivery of the placenta. Labor typically begins at some point when the fetus is considered full term—between 37 and 42 weeks’ gestation.
In the third trimester, before labor starts, a woman might have a plug of mucus and blood fall out of the opening to the cervix, sometimes called a “bloody show”. Other times the amniotic sac might rupture, sometimes called “water breaking”. Either of these can trigger the onset of labor and so-called true labor contractions. These guys have to be distinguished from the milder and ineffective false labor contractions, also called Braxton Hicks contractions (or sometimes called practice contractions). Once they start, true labor contractions progress in frequency, duration, and intensity, and they can feel like waves that build up to a peak intensity and then gradually decrease.
The contractions pull on the thick tissues of the cervix, causing it to efface or get thinner and also dilate or open up, so then the fetus can leave the uterus and enter the world. From the moment true contractions begin to the baby’s delivery usually takes about 12 to 18 hours for a first-time pregnancy, and about half that time for subsequent pregnancies. Although, as any mother knows, this time can vary a lot!
Even though labor is a continuous process, it can be broken down into three stages. Additionally, this first stage is subdivided into two phases. The first phase is the early phase or latent phase, and usually lasts up to 20 hours, or until the cervix dilates to 6 centimeters. At first, there are irregular contractions that occur every 5 - 30 minutes and last about 30 seconds each, causing the cervix to dilate from 0 cm to about 3 cm and efface from about 0% - 30%.Then, regular contractions follow - they happen every 3 - 5 minutes and last about a minute or more, and this causes the cervix to dilate from 3 cm to about 6 cm and efface to about 80%. This marks the beginning of the active phase of labor, during which the cervix dilates from 6 to 10 centimeters and effaces to 100%. Contractions are very intense, lasting between 60 to 90 seconds each, with only 30 seconds to 2 minutes of rest in between - so sometimes they even overlap a bit, with one contraction beginning before the previous one is done. Also, the amniotic sac often ruptures at this point if it hasn’t already.
Now that the cervix is fully dilated, we enter the second stage of labor can be thought of as the pushing stage. During this stage, the critical thing is for the baby, and in particular the baby’s head, to navigate through the maternal pelvis, and this depends on the “3 Ps” - power, passenger, and passage. Power refers to forceful uterine contractions, passenger refers to the fetus, and passage refers to the route that the fetus has to travel through the bony pelvis. In fact, the relationship between the baby’s head and the bony pelvis is so critical, that human babies have evolved with unfused skulls, just so their head can be as large as possible and still successfully and safely make that passage through the pelvis into the world.
Now there are a few factors that determine how easy this passage is for the fetus. First is fetal size, the critical factor is the size of the fetal head.
Also though there’s fetal attitude, which refers to the way that the fetal body is flexed, not its personality. When labor starts, the fetus is normally fully flexed, which means the chin is on the chest, and they have a rounded back with flexed arms and legs. In this position, the smallest diameter (which is referred to as the suboccipitobregmatic diameter) presents at the pelvic inlet.
Larger fetuses and those that aren’t completely flexed have more difficulty making it through the passage. Next there’s fetal lie, which describes how the fetus is positioned in the uterus.
A longitudinal fetal lie is ideal, where the long axis of the fetus, which is its spine, lies along the maternal long axis—the mom’s spine. The fetus can also be transverse though, where the fetal spine is perpendicular to mom’s spine, or it can be oblique, where it’s slightly at an angle, and these two positions can impede the progression of labor.
Finally, there’s fetal presentation which refers to the first fetal part, called the presenting part, to descend into the pelvic inlet. Cephalic, or head-first, is the first type, and furthermore the most common and optimal presentation for easy delivery is a type of cephalic presentation called vertex, which includes complete flexion of the head as well. Also though, there’s breech presentation (which is head up, so the bottom, feet, or knees present first), as well as shoulder (where the shoulders present first).
To make it through the passage, the fetus makes several positional changes which are called cardinal movements or mechanisms of labor. Initially there is descent, which is the downward movement of the fetus to the pelvic inlet. The degree of descent is called the fetal station, which is described in terms of the relationship of the presenting part to mom’s ischial spines.
The fetus moves from the pelvic inlet (which is about minus 5 station) down to the ischial spines (which is station 0), and this position’s called engagement.
Then there’s flexion, where the fetal chin presses against its chest as its head meets resistance from the pelvic floor.
Next there’s internal rotation, where the fetal shoulders internally rotate by 45 degrees so the widest part of the shoulders are in line with the widest part of the pelvic inlet.
After the fetal head passes under the symphysis pubis (which is at about +4 station), there’s extension, which is where the fetal head will change from flexion to extension, and then they move to about +5 station and emerge from the vagina.
After the delivery of the head, there’s restitution, where the head externally rotates so that the shoulders can pass through the pelvic outlet and under the symphysis pubis.
And finally there’s expulsion, where the anterior shoulder slips under the symphysis pubis, followed by the posterior shoulder, and then finally followed by the rest of the body. This marks the end of the second stage of labor.
The third stage of labor occurs after the baby has been delivered, and involves delivery of the placenta. After the baby is delivered, the uterus contracts firmly and the placenta begins to separate from the uterine wall. It’s then carefully removed to ensure that there are no placental remnants left in the uterus.
Sometimes the several-hours after delivery is called the “fourth stage”, because there are major physiologic changes like adaptation to the blood loss, and the start of uterine involution, where the uterus begins returning to its pre-pregnant state.
Alright, as a quick recap, labor is composed of 3 stages. The first stage starts with true labor contractions and ends when the cervix is completely effaced and dilated. The second stage is the pushing stage, which ends with the birth of the baby. The third stage ends with delivery of the placenta.
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Stages of labor references
1. Lawrence A, Lewis L, Hofmeyr GJ, Styles C: Maternal positions and mobility during first stage labour. Cochrane Database Syst Rev (8):CD003934, 2013. doi: 10.1002/14651858.CD003934.pub3
2. Aasheim V, et al: Perineal techniques during the second stage of labour for reducing perineal trauma. Cochrane Database Syst Rev 6:CD006672, 2017. doi: 10.1002/14651858.CD006672.pub3
3. Gupta JK, Sood A, Hofmeyr GJ, et al: Position in the second stage of labour for women without epidural anaesthesia. Cochrane Database Syst Rev 5:CD002006, 2017. doi: 10.1002/14651858.CD002006.pub4
4. Lemos A, Amorim MM, Dornelas de Andrade A, et al: Pushing/bearing down methods for the second stage of labour. Cochrane Database Syst Rev. 3:CD009124, 2017. doi: 10.1002/14651858.CD009124.pub3
Rupture of membranes
Occasionally, the membranes (amniotic and chorionic sac) rupture before labor begins, and amniotic fluid leaks through the cervix and vagina. Rupture of membranes at any stage before the onset of labor is called premature rupture of membranes Prelabor Rupture of Membranes (PROM) Prelabor rupture of membranes is leakage of amniotic fluid before onset of labor. Diagnosis is clinical. Delivery is recommended when gestational age is ≥ 34 weeks and is generally indicated... read more (PROM). Some women with PROM feel a gush of fluid from the vagina, followed by steady leaking.
Further confirmation is not needed if during examination, fluid is seen leaking from the cervix. Confirmation of more subtle cases may require testing. For example, the pH of vaginal fluid may be tested with Nitrazine paper, which turns deep blue at a pH > 6.5 (pH of amniotic fluid: 7.0 to 7.6); false-positive results can occur if vaginal fluid contains blood or semen or if certain infections are present. A sample of the secretions from the posterior vaginal fornix or cervix may be obtained, placed on a slide, air dried, and viewed microscopically for ferning. Ferning (crystallization of sodium chloride in a palm leaf pattern in amniotic fluid) usually confirms rupture of membranes.
If rupture is still unconfirmed, ultrasonography showing oligohydramnios (deficient amniotic fluid) provides further evidence suggesting rupture. Rarely, amniocentesis with instillation of dye is done to confirm rupture; dye detected in the vagina or on a tampon confirms rupture.
When a woman’s membranes rupture, she should contact her physician immediately. About 80 to 90% of women with PROM at term ( ≥ 37 weeks) and about 50% of women with preterm PROM (< 37 weeks) go into labor spontaneously within 24 hours; > 90% of women with PROM go into labor within 2 weeks. The earlier the membranes rupture before 37 weeks, the longer the delay between rupture and labor onset. If membranes rupture at term but labor does not start within several hours, labor is typically induced to lower risk of maternal and fetal infection.
Most women prefer hospital delivery, and most health care practitioners recommend it because unexpected maternal and fetal complications may occur during labor and delivery or postpartum, even in women without risk factors. About 30% of hospital deliveries involve an obstetric complication Introduction to Abnormalities and Complications of Labor and Delivery Abnormalities and complications of labor and delivery should be diagnosed and managed as early as possible. Most of the following complications are evident before onset of labor: Multifetal... read more (eg, laceration, postpartum hemorrhage Postpartum Hemorrhage Postpartum hemorrhage is blood loss of > 1000 mL or blood loss accompanied by symptoms or signs of hypovolemia within 24 hours of birth. Diagnosis is clinical. Treatment depends on etiology... read more ). Other complications include abruptio placentae Placental Abruption (Abruptio Placentae) Placental abruption (abruptio placentae) is premature separation of the placenta from the uterus, usually after 20 weeks gestation. It can be an obstetric emergency. Manifestations may include... read more , abnormal fetal heart rate pattern, shoulder dystocia Fetal Dystocia Fetal dystocia is abnormal fetal size or position resulting in difficult delivery. Diagnosis is by examination, ultrasonography, or response to augmentation of labor. Treatment is with physical... read more , need for emergency cesarean delivery Cesarean Delivery Cesarean delivery is surgical delivery by incision into the uterus. Up to 30% of deliveries in the US are cesarean. The rate of cesarean delivery fluctuates. It has recently increased, partly... read more , and neonatal depression or abnormality.
Nonetheless, many women want a more homelike environment for delivery; in response, some hospitals provide birthing facilities with fewer formalities and rigid regulations but with emergency equipment and personnel available. Birthing centers may be freestanding or located in hospitals; care at either site is similar or identical. In some hospitals, certified nurse-midwives provide much of the care for low-risk pregnancies. Midwives work with a physician, who is continuously available for consultation and operative deliveries (eg, by forceps, vacuum extractor, or cesarean). All birthing options should be discussed.
For many women, presence of the their partner or another support person during labor is helpful and should be encouraged. Moral support, encouragement, and expressions of affection decrease anxiety and make labor less frightening and unpleasant. Childbirth education classes can prepare parents for a normal or complicated labor and delivery. Sharing the stresses of labor and the sight and sound of their own child tends to create strong bonds between the parents and between parents and child.
The parents should be fully informed of any complications.
Typically, pregnant women are advised to go to the hospital if they believe their membranes have ruptured or if they are experiencing contractions lasting at least 30 seconds and occurring regularly at intervals of about 6 minutes or less. Within an hour after presentation at a hospital, whether a woman is in labor can usually be determined based on the following:
Occurrence of regular and sustained painful uterine contractions
Complete cervical effacement
If these criteria are not met, false labor may be tentatively diagnosed, and the pregnant woman is typically observed for a time and, if labor does not begin within several hours, is sent home.
When pregnant women are admitted, their blood pressure, heart and respiratory rates, temperature, and weight are recorded, and presence or absence of edema is noted. A urine specimen is collected for protein and glucose analysis, and blood is drawn for a complete blood count (CBC), blood typing, and antibody screening. If routine laboratory tests were not done during prenatal visits, they should be done; these tests include screening for HIV, hepatitis B, syphilis, and group B streptococcal infection.
A physical examination is done. While examining the abdomen, the clinician estimates size, position, and presentation of the fetus, using the Leopold maneuver (see figure Leopold maneuver Leopold maneuver ). The clinician notes the presence and rate of fetal heart sounds, as well as location for auscultation. Preliminary estimates of the strength, frequency, and duration of contractions are also recorded.
A helpful mnemonic device for evaluation is the 3 Ps:
Powers (contraction strength, frequency, and duration)
Passage (pelvic measurements)
Passenger (eg, fetal size, position, heart rate pattern)
(A) The uterine fundus is palpated to determine which fetal part occupies the fundus. (B) Each side of the maternal abdomen is palpated to determine which side is fetal spine and which is the extremities. (C) The area above the symphysis pubis is palpated to locate the fetal presenting part and thus determine how far the fetus has descended and whether the fetus is engaged. (D) One hand applies pressure on the fundus while the index finger and thumb of the other hand palpate the presenting part to confirm presentation and engagement.
If labor is active and the pregnancy is at term, a clinician examines the vagina with 2 fingers of a gloved hand to evaluate progress of labor. If bleeding (particularly if heavy) is present, the examination is delayed until placental location is confirmed by ultrasonography. If bleeding results from placenta previa, vaginal examination can initiate severe hemorrhage.
If labor is not active but membranes are ruptured, a speculum examination is done initially to document cervical dilation and effacement and to estimate station (location of the presenting part); however, digital examinations are delayed until the active phase of labor or problems (eg, decreased fetal heart sounds) occur. If the membranes have ruptured, any fetal meconium (producing greenish-brown discoloration) should be noted because it may be a sign of fetal stress. If labor is preterm (< 37 weeks) or has not begun, only a sterile speculum examination should be done, and a culture should be taken for gonococci, chlamydiae, and group B streptococci.
Cervical dilation is recorded in centimeters as the diameter of a circle; 10 cm is considered complete.
Effacement is estimated in percentages, from zero to 100%. Because effacement involves cervical shortening as well as thinning, it may be recorded in centimeters using the normal, uneffaced average cervical length of 3.5 to 4.0 cm as a guide.
Station is expressed in centimeters above or below the level of the maternal ischial spines. Level with the ischial spines corresponds to 0 station; levels above (+) or below (−) the spines are recorded in cm increments. Fetal lie, position, and presentation are noted.
Lie describes the relationship of the long axis of the fetus to that of the mother (longitudinal, oblique, transverse).
Position describes the relationship of the presenting part to the maternal pelvis (eg, occiput left anterior [OLA] for cephalic, sacrum right posterior [SRP] for breech).
Presentation describes the part of the fetus at the cervical opening (eg, breech, vertex, shoulder).
Preparation for delivery
Women are admitted to the labor suite for frequent observation until delivery. If labor is active, they should receive little or nothing by mouth to prevent possible vomiting and aspiration during delivery or in case emergency delivery with general anesthesia is necessary.
Shaving or clipping of vulvar and pubic hair is not indicated, and it increases the risk of wound infections.
An IV infusion of Ringer's lactate may be started, preferably using a large-bore indwelling catheter inserted into a vein in the hand or forearm. During a normal labor of 6 to 10 hours, women should be given 500 to 1000 mL of this solution. The infusion prevents dehydration during labor and subsequent hemoconcentration and maintains an adequate circulating blood volume. The catheter also provides immediate access for drugs or blood if needed. Fluid preloading is valuable if epidural or spinal anesthesia is planned. If instrumental or cesarean delivery seems unlikely, women may drink clear liquids.
Analgesics may be given during labor as needed, but only the minimum amount required for maternal comfort should be given because analgesics cross the placenta and may depress the neonate’s breathing. Neonatal toxicity can occur because after the umbilical cord is cut, the neonate, whose metabolic and excretory processes are immature, clears the transferred drug much more slowly by liver metabolism or by urinary excretion. Preparation for and education about childbirth lessen anxiety.
Physicians are increasingly offering epidural injection (providing regional anesthesia) as the first choice for analgesia during labor. Typically, a local anesthetic (eg, 0.2% ropivacaine, 0.125% bupivacaine) is continuously infused, often with an opioid (eg, fentanyl, sufentanil), into the lumbar epidural space. Initially, the anesthetic is given cautiously to avoid masking the awareness of pressure that helps stimulate pushing and to avoid motor block. Women should be reassured that epidural analgesia does not increase the risk of cesarean delivery (1 Analgesia references Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ).
If epidural injection is inadequate or if IV administration is preferred, fentanyl (100 mcg) or morphine sulfate (up to 10 mg) given IV every 60 to 90 minutes is commonly used. These opioids provide good analgesia with only a small total dose. If neonatal toxicity results, respiration is supported, and naloxone 0.01 mg/kg can be given IM, IV, subcutaneously, or endotracheally to the neonate as a specific antagonist. Naloxone may be repeated in 1 to 2 minutes as needed based on the neonate’s response. Clinicians should check the neonate 1 to 2 hours after the initial dosing with naloxone because the effects of the earlier dose abate.
If fentanyl or morphine provides insufficient analgesia, an additional dose of the opioid or another analgesic method should be used rather than the so-called synergistic drugs (eg, promethazine), which have no antidote. (These drugs are actually additive, not synergistic.) Synergistic drugs are still sometimes used because they lessen nausea due to the opioid; doses should be small.
1. Practice Guidelines for Obstetric Anesthesia: An Updated Report by the American Society of Anesthesiologists Task Force on Obstetric Anesthesia and the Society for Obstetric Anesthesia and Perinatology*. Anesthesiology 124:270–300, 2016. doi: 10.1097/ALN.0000000000000935
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 Fetal Monitoring Definitions ).
Several patterns are recognized; they are classified into 3 tiers (categories [ 1 Fetal monitoring reference Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more ]), which usually correlate with the acid–base status of the fetus:
Category I: Normal
Category II: Indeterminate
Category III: Abnormal
A normal pattern strongly 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.
An indeterminate pattern is 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.
An abnormal pattern usually 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 of oxytocin) 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 oximetry has 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).
A nonstress test records 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.
A biophysical profile 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 high-risk pregnancies Overview of High-Risk Pregnancy In a high-risk pregnancy, the mother, fetus, or neonate is at increased risk of morbidity or mortality before, during, or after delivery. Risk assessment is part of routine prenatal care. Family... read more (eg, complicated by maternal diabetes or hypertension or by stillbirth or fetal growth restriction in a previous pregnancy).
Contraction stress testing (oxytocin challenge test) is now rarely done. In this test, fetal movements and HR are monitored (typically externally) during contractions induced by oxytocin. 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.
Fetal monitoring reference
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 Nurs 37 (5):510–515, 2008. doi: 10.1111/j.1552-6909.2008.00284.x
Drugs Mentioned In This Article
|Drug Name||Select Trade|
|4-Way Saline, Adsorbonac, Altamist, Ayr Allergy & Sinus, Ayr Baby Saline, Ayr Saline Nasal, BD Posiflush Normal Saline, BD Posiflush Sterile Field Normal Saline, BD Posiflush SureScrub Normal Saline, Blairex Broncho Saline, Breathe Free Saline, Deep Sea , Entsol, HyperSal, Hyper-Sal, Hypertears, Little Remedies for Noses, Little Remedies Stuffy Nose, Monoject Sodium Chloride, Muro 128, NebuSal , Ocean, Ocean Complete, Ocean For Kids, Pediamist, PULMOSAL, Rhinaris, Rhinaris Lubricating, Saljet , Saljet Rinse, SaltAire, Sea Soft, Trichotine, Wound Wash, XYNASE, ZARBEE'S Soothing Saline Nasal Mist|
|Marcaine, Marcaine Spinal, POSIMIR, Sensorcaine, Sensorcaine MPF , Xaracoll|
|ABSTRAL, Actiq, Duragesic, Fentora, IONSYS, Lazanda, Onsolis, Sublimaze, SUBSYS|
|ARYMO ER, Astramorph PF, Avinza, DepoDur, Duramorph PF, Infumorph, Kadian, MITIGO, MORPHABOND, MS Contin, MSIR, Opium Tincture, Oramorph SR, RMS, Roxanol, Roxanol-T|
|EVZIO, Kloxxado, Narcan, ZIMHI|
|Anergan-50, Pentazine , Phenadoz , Phenergan, Phenergan Fortis, Prometh Plain, Promethegan|