Labor consists of a series of rhythmic, involuntary, progressive contractions of the uterus that cause effacement (thinning and shortening) and dilation of the uterine cervix. 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 wk (before or after) the estimated delivery date. In a first pregnancy, labor usually lasts 12 to 18 h on average; subsequent labors are often shorter, averaging 6 to 8 h. Management of complications during labor requires additional measures (see Abnormalities and Complications of Labor and Delivery: Alternatives to Spontaneous Labor and Delivery).
Beginning 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 h. Bloody show can be differentiated from abnormal 3rd-trimester vaginal bleeding because the amount is small, bloody show is typically mixed with mucus, and the pain due to abruptio placentae (premature separation) is absent. In most pregnant women, previous ultrasonography has been done and ruled out placenta previa. 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. Digital vaginal examination is contraindicated, and ultrasonography is done as soon as possible.
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 better 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 h in nulliparas and 5 h in multiparas; duration is considered abnormal if it lasts > 20 h in nulliparas or > 12 h 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 h in nulliparas and 2 to 4 h in multiparas. The cervix should dilate 1.2 cm/h in nulliparas and 1.5 cm/h in multiparas. Pelvic examinations are done every 2 to 3 h to evaluate labor progress. Lack of progress in dilation and descent of the presenting part may indicate dystocia (fetopelvic disproportion). If the membranes have not spontaneously ruptured, some clinicians routinely use amniotomy (artificial rupture of membranes) 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.
Maternal heart rate and BP and fetal heart rate should be checked continuously by electronic monitoring or intermittently by auscultation during the 1st stage of labor (see Normal Pregnancy, Labor, and Delivery: Fetal Monitoring). 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 h in nulliparas (median 50 min) and 1 h in multiparas (median 20 min). 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.
The 3rd stage of labor begins after delivery of the infant and ends with delivery of the placenta.
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 (PROM—see Abnormalities and Complications of Labor and Delivery: Premature Rupture of Membranes (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 NaCl 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 and about 50% of women with PROM preterm go into labor spontaneously within 24 h; > 90% of women with PROM go into labor within 2 wk. The earlier the membranes rupture before 37 wk, 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 (eg, laceration, postpartum hemorrhage). Other complications include abruptio placentae, nonreassuring fetal heart rate pattern, shoulder dystocia, need for emergency cesarean delivery, 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 father 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 sec and occurring regularly at intervals of about ≤ 6 min. Within an hour after presentation at a hospital, whether a woman is in labor can usually be determined based on occurrence of regular and sustained painful uterine contractions, bloody show, membrane rupture, and 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 BP, 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 CBC and blood typing. A physical examination is done. While examining the abdomen, the clinician estimates size, position, and presentation of the fetus, using Leopold's maneuvers (see Fig. 1: Normal Pregnancy, Labor, and Delivery: 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), and passenger (eg, fetal size, position, heart rate pattern).
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 wk) 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 0 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); presentation describes the part of the fetus at the cervical opening (eg, breech, vertex, shoulder). 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).
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. Enemas and shaving or clipping of vulvar hair are no longer indicated. 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 h, 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.
Analgesics may be given during labor as needed, but as little as possible should be given because they 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, markedly decreasing the need for analgesics.
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; both effects can slow labor.
If epidural injection is inadequate or if IV administration is preferred, fentanyl (100 ug), meperidine (up to 25 mg), or morphine sulfate (up to 10 mg) given IV q 60 to 90 min is commonly used. These opioids provide good analgesia with only a small total dose. If toxicity results, respiration is supported, and naloxone 0.01 mg/kg can be given IM, IV, sc, or endotracheally to the neonate as a specific antagonist. Naloxone may be repeated in 1 to 2 min as needed based on the neonate's response. Clinicians should check the neonate 1 to 2 h after the initial dosing with naloxone because the effects of the earlier dose abate. If fentanyl, meperidine, 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.
Fetal status must be monitored during labor. The main parameters are fetal heart rate (HR) and fetal HR variability, particularly as it relates to uterine contractions and maternal movement. Several patterns are recognized. One is considered normal and reassuring; the others are considered abnormal and nonreassuring. A normal pattern is a baseline HR with the following characteristics:
Patterns that indicate possible nonreassuring fetal heart status include the following:
Nonreassuring patterns require more intensive monitoring.
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. Although this practice has been lifesaving, its value is debated, partly because many apparent abnormalities are false positives, leading to unnecessary cesarean deliveries. Rate of cesarean delivery is higher among women monitored electronically than among those monitored by auscultation. Fetal pulse oximetry is being studied as a way to confirm abnormal or equivocal results of electronic monitoring; fetal oxygenation may help determine whether a cesarean delivery is needed. For oximetry, an internal sensor must be placed inside the uterus and against the fetal skin to ensure an accurate reading of fetal oxygenation. However, fetal pulse oximetry does not appear to change the rate of cesarean delivery from that based on results of fetal HR monitoring alone.
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 min during the 1st stage of labor and every 15 min during the 2nd stage. For high-risk pregnancies, fetal HR must be checked every 15 min during the 1st stage and every 3 to 5 min during the 2nd stage. Listening for at least 1 to 2 min 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.
For external electronic fetal HR monitoring, devices are applied to the maternal abdomen to record fetal heart sounds and uterine contractions. For internal monitoring, 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 sensor is not functioning correctly).
External electronic fetal monitoring can be used during labor or electively to continuously record fetal HR and correlate it with fetal movements (called a nonstress test). A nonstress test is interpreted as nonreassuring if no accelerations occur during a 40-min period. External monitoring can be used similarly with a contraction stress test; fetal movements and HR are monitored during contractions induced by oxytocin (oxytocin challenge test) or breast stimulation or during spontaneous contractions. Nonstress and contraction stress tests are frequently used to monitor complicated or high-risk pregnancies (eg, complicated by maternal diabetes or hypertension or by prior stillbirth or fetal growth restriction).
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 O2 via a tight non-rebreather 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 cesarean delivery is needed.
Last full review/revision June 2007 by Haywood L. Brown, MD