INTRODUCTION — Identifying patients with preterm contractions who will go on to give birth preterm is an inexact process, even though preterm labor is one of the most common reasons for hospitalization in pregnancy. Accurate identification of patients in true preterm labor allows appropriate application of interventions that can improve neonatal outcome: antenatal corticosteroid therapy, antibiotic prophylaxis against early-onset neonatal group B streptococcal infection, magnesium sulfate for neuroprotection, and maternal transfer to a facility with an appropriate level of newborn care (if necessary). Just as important, accurate identification of patients who are contracting but not in preterm labor avoids unnecessary and sometimes costly interventions in the approximately 50 percent of patients with suspected preterm labor who subsequently give birth at term without tocolytic therapy [1].
This topic will describe the clinical findings and diagnostic evaluation of patients who present with signs and symptoms of preterm labor, and initial treatment of those in whom a diagnosis of preterm labor is made. Risk factors, prevention, and tocolytic therapy for preterm labor are discussed separately. (See "Preterm birth: Risk factors, interventions for risk reduction, and maternal prognosis" and "Inhibition of acute preterm labor".)
PATHOGENESIS OF PRETERM LABOR — The pathophysiology of preterm labor involves at least four primary pathogenic processes that result in a final common pathway ending in spontaneous preterm labor and birth:
●Stress-induced premature activation of the maternal or fetal hypothalamic-pituitary-adrenal axis
●Exaggerated inflammatory response/infection and/or altered genital tract microbiome
●Decidual hemorrhage
●Pathological uterine distention
These processes and the pathophysiology of normal labor are discussed in detail separately. (See "Spontaneous preterm birth: Pathogenesis" and "Physiology of parturition at term".)
CLINICAL FINDINGS — The clinical findings that define true labor (ie, regular contractions resulting in cervical change) are the same whether labor occurs preterm or at term. The following prodromal signs and symptoms may be present for several hours before diagnostic criteria for labor are met:
●Menstrual-like cramping
●Mild, irregular contractions
●Low back ache
●Pressure sensation in the vagina or pelvis
●Vaginal discharge of mucus, which may be clear, pink, or slightly bloody (ie, mucus plug, bloody show)
●Spotting, light bleeding
Uterine contractions are the sine qua non of labor, but mild irregular contractions are a normal finding at all stages of pregnancy, thereby adding to the challenge of distinguishing true labor (contractions that result in cervical change) from false labor (contractions that do not result in cervical change [ie, Braxton Hicks contractions]). True labor is more likely when an increasing contraction frequency is accompanied by increasing intensity and duration since an increase in the frequency alone may occur transiently, especially at night and with advancing gestational age. Although many investigators have tried, no one has been able to identify a threshold contraction frequency that effectively identifies patients who will progress to true labor. Only 13 percent of patients presenting at <34 weeks of gestation who meet explicit contraction criteria for preterm labor give birth within one week [2].
Cervical changes on physical examination that precede or accompany true labor include dilation, effacement, softening, and movement to a more anterior position. The rate of cervical change distinguishes cervical ripening, which occurs over days to weeks, from true labor, in which cervical change occurs over minutes to hours. A short or a dilated cervix may be the first clinical manifestation of impending preterm labor triggered by subclinical inflammation [3].
COMPONENTS OF THE DIAGNOSTIC EVALUATION — In most patients, the diagnostic evaluation is performed on the labor unit or a labor triage unit. However, the clinician may elect to evaluate patients with very mild, nonspecific symptoms in the office.
History and initial examinations — For the initial evaluation of patients with suspected preterm labor, the clinician should:
●Review the patient's past and present obstetric and medical history, including risk factors for preterm birth (table 1). A standardized interview to screen for substance misuse is part of this review; some examples are shown in the table (table 2). (See "Substance use during pregnancy: Screening and prenatal care", section on 'Screening for substance use'.)
Although many cases appear to be idiopathic, clinicians should consider possible causes of the preterm contractions based on the history and physical examination. Preterm labor may be triggered by an underlying obstetric complication (eg, abruption) or medical/surgical disorder (eg, appendicitis, bowel obstruction or strangulation, pyelonephritis, acute cholecystitis, pneumonia, hyperthyroidism/thyroid storm) that requires specific intervention. These cases may present with additional symptoms and/or symptoms atypical for preterm labor. Sometimes, accurate diagnosis requires a high index of suspicion since laboring patients typically have abdominal pain and may have back pain, nausea, vomiting, or diarrhea.
●Estimate gestational age, based on the best estimate from the first ultrasound examination [4]. If prior ultrasound estimation of gestational age is not available, an ultrasound examination for fetal biometry should be performed. (See "Prenatal assessment of gestational age, date of delivery, and fetal weight".)
●Evaluate for signs and symptoms of preterm labor. (See 'Clinical findings' above.)
●Assess contraction frequency, duration, and intensity. (See "Labor and delivery: Management of the normal first stage", section on 'Uterine contraction monitoring'.)
●Examine the uterus to assess firmness, tenderness, fetal size, and fetal position.
●Review the fetal heart rate tracing. (See "Intrapartum fetal heart rate monitoring: Overview".)
Speculum examination — A speculum examination is performed using a wet non-lubricated speculum (lubricants may interfere with tests performed on vaginal specimens). The goals of this examination are to:
●Estimate cervical dilation. Cervical dilation ≥3 cm supports the diagnosis of preterm labor.
●Assess the presence and amount of uterine bleeding. Bleeding from placental abruption or placenta previa can trigger preterm labor. (See "Acute placental abruption: Pathophysiology, clinical features, diagnosis, and consequences" and "Placenta previa: Epidemiology, clinical features, diagnosis, morbidity and mortality".)
●Assess fetal membrane status (intact or ruptured) by standard methods. Preterm prelabor rupture of membranes (PPROM) often precedes or occurs during preterm labor. Diagnosis and management of PPROM are reviewed separately. (See "Preterm prelabor rupture of membranes: Clinical manifestations and diagnosis".)
●Use a swab to obtain a cervicovaginal fluid specimen in case fetal fibronectin (fFN) testing is subsequently desired. The swab is rotated in the posterior fornix for 10 seconds.
"Blind" sampling without a speculum is also acceptable. In one method, the posterior vaginal wall is depressed with an unlubricated, gloved finger and then the polyester swab is slowly passed along the finger toward the posterior fornix until resistance is felt [5]. In another method, the labia are held apart and then the swab is blindly inserted into the vagina and directed slowly toward the posterior fornix until meeting resistance [6]. In both methods, it is important to stop at the first sign of resistance to avoid rupturing exposed membranes, if present. (See 'Fetal fibronectin for selected patients' below.)
Digital cervical examination — In most patients, cervical dilation and effacement are assessed by digital examination after placenta previa and rupture of membranes have been excluded by history and physical, laboratory, and ultrasound examinations, as appropriate. A digital examination should be performed before speculum examination if the information is urgently needed to care for the patient (eg, abnormal fetal heart rate, probable advanced phase of active labor) and placenta previa is unlikely. As discussed above, cervical dilation >3 cm in the presence of uterine contractions at 20+0 to 36+6 weeks supports the diagnosis of preterm labor; inhibition of acute preterm labor is less likely to be successful as the cervix dilates beyond 3 cm.
When assessing cervical dilation and effacement in the second trimester, it is important to distinguish between patients whose membranes have hour-glassed (prolapsed) through a mildly dilated and effaced cervix (which is suggestive of cervical insufficiency) and those who are in active labor with advanced cervical dilation and effacement. Transvaginal ultrasound (TVUS) assessment of the cervix can help distinguish between the two entities when the diagnosis is uncertain. (See "Cervical insufficiency", section on 'Physical examination-based cervical insufficiency' and "Transvaginal cervical cerclage", section on 'Replace prolapsed membranes, if present'.)
Transvaginal ultrasound examination — TVUS measurement of cervical length is useful for supporting or excluding the diagnosis of preterm labor when the diagnosis is unclear. A short cervix (defined here as <30 mm) before 34 weeks of gestation is predictive of an increased risk for preterm birth in all populations, while a long cervix (defined here as ≥30 mm) has a high negative predictive value for preterm birth. Knowledge of cervical length in patients with threatened preterm labor may improve outcome, particularly avoidance of unnecessary hospitalization and interventions when the cervix is long, but data are limited [7].
The procedure for measurement of cervical length is described separately. (See "Short cervix before 24 weeks: Screening and management in singleton pregnancies".)
Obstetric ultrasound examination — Obstetric ultrasound examination provides useful information besides cervical length, including presence/absence of fetal, placental, and maternal anatomic abnormalities; confirmation of fetal presentation; assessment of amniotic fluid volume; and estimated fetal weight. This information may be used for counseling patients about the potential causes and outcomes of preterm birth and determining the best route of birth.
Laboratory evaluation
Overview — We order the following laboratory tests:
●Rectovaginal group B streptococcal (GBS) culture, if not done within the previous five weeks; antibiotic prophylaxis against GBS depends on the results. (See "Prevention of early-onset group B streptococcal disease in neonates", section on 'Special populations'.)
●Urine culture since asymptomatic bacteriuria and pyelonephritis are associated with an increased risk of preterm labor and birth. (See "Urinary tract infections and asymptomatic bacteriuria in pregnancy".)
●fFN in pregnancies <34 weeks of gestation with intact membranes, cervical dilation <3 cm, and cervical length 20 to 30 mm on TVUS examination. (See 'Cervical length 20 to <30 mm' below.)
●Testing for sexually transmitted infections (eg, chlamydia, gonorrhea, syphilis), depending on the patient's risk factors for these infections and, if indicated, whether antepartum testing for the infections was recently performed. (See "Prenatal care: Second and third trimesters", section on 'Screen for sexually transmitted infections'.)
Fetal fibronectin for selected patients — fFN is an extracellular matrix protein present at the decidual-chorionic interface. Disruption of this interface due to subclinical infection or inflammation, abruption, or uterine contractions releases fFN into cervicovaginal secretions, which is the basis for its use as a marker for predicting spontaneous preterm birth [8].
Measurement of fFN is performed to distinguish true preterm labor from false labor. Theoretically, accurate identification of true preterm labor provides an opportunity for interventions that can improve neonatal outcome (eg, antenatal corticosteroid therapy, antibiotic prophylaxis against group B streptococcal infection, magnesium sulfate for neuroprotection, transfer to a facility with an appropriate level nursery, if necessary). The ability to rule out true preterm labor should avoid unnecessary and sometimes costly intervention for the approximately 50 percent of patients who will subsequently give birth at term despite not receiving tocolytic therapy [1].
However, fFN results alone are not useful [9,10]. In a systematic review of six randomized trials in which a total of 546 patients with threatened preterm labor were randomly assigned to management with reported or concealed fFN results, clinician knowledge of fFN results did not reduce rates of maternal hospitalization (risk ratio [RR] 1.06, 95% CI 0.79-1.43) or preterm birth <34 weeks (RR 1.09, 95% CI 0.54-2.18) [11]. Use of tocolytics and betamethasone, gestational age at birth, rate of respiratory distress syndrome, and number of days in a neonatal intensive care unit were similar for both groups [9]. An unexpected finding was that costs were higher in the reported group, suggesting that physicians placed greater significance on positive test results than on negative results, resulting in an overall increase in health care utilization [12]. The review excluded trials in which management involved use of both fFN and sonographic cervical length, which is our approach. We obtain fFN selectively, limiting its use to patients with cervical length 20 to 30 mm. (See 'Cervical length 20 to <30 mm' below.)
Qualitative fFN — Qualitative fFN results are reported as positive or negative. A positive fFN test refers to a fFN concentration ≥50 ng/mL in cervicovaginal fluid between 22+0 and 34+6 weeks of gestation in patients with intact membranes, cervical dilation <3 cm, and no gross vaginal bleeding. A positive fFN result correlates with an increased risk of preterm birth within seven days.
In patients with signs and symptoms of preterm labor, a systematic review of five randomized trials and 15 diagnostic test accuracy studies evaluating cervicovaginal fFN for predicting preterm birth reported the following pooled estimates [13]:
●Birth within 7 to 10 days of testing – Sensitivity and specificity 76.7 and 82.7 percent, respectively
●Birth <34 weeks of gestation – Sensitivity and specificity 69.1 and 84.4 percent, respectively
●Birth <37 weeks of gestation – Sensitivity and specificity 60.8 and 82.3 percent, respectively
Positive and negative predictive values depend on the prevalence of preterm birth in the population. In a systematic review in which the prevalence of preterm birth within seven days of sampling varied from 2 to 30 percent among the included studies, the overall pretest probability of birth within seven days of testing was 7.7 percent, and based on positive or negative fFN results, the posttest probabilities were 25.9 and 2.4 percent, respectively [14].
False-positive results can occur due to ejaculate from coitus within the previous 24 hours, a grossly bloody specimen, or digital cervical examination [15-17]. Theoretically, TVUS examination may cause a false positive result, but in one study all 25 patients with a negative baseline fFN test had a second negative fFN test post-ultrasound [18]. Administration of intravaginal substances, such as lubricants, medications, or douching may interfere with the assay [19].
Quantitative fFN — Quantitative measurement of fFN appears to improve predictive value compared with use of the qualitative test using a 50 ng/mL threshold [20-22]. In symptomatic patients, the positive predictive values of fFN thresholds of 10, 50, 200, and 500 ng/mL for preterm birth within 14 days were 11, 20, 37, and 46 percent, respectively, in a prospective blinded study [20]. For preterm birth <34 weeks of gestation, positive predictive values for the same thresholds were 19, 32, 61, and 75 percent, respectively. Instrumentation for quantitative measurement of fFN is not commercially available in the United States.
The combination of quantitative fFN testing and cervical length measurement in symptomatic patients increases predictive value [23]. An algorithm combining quantitative fFN and cervical length, demographic information, and obstetric history (previous spontaneous preterm birth/preterm prelabor rupture of membranes or suspected preterm labor) has been incorporated into the Quantitative Instrument for the Prediction of Preterm birth App (QUiPP) for prediction of spontaneous preterm birth in Europe [24-27].
Other laboratory tests — Like fFN, placental alpha-microglobulin-1 (PAMG-1) [28-30] or insulin-like growth factor binding protein-1 (IGFBP-1) [31] in vaginal or cervical secretions suggests disruption of the fetal membranes (prelabor rupture of membranes [PROM] or labor) and are potential markers of an increased risk of preterm birth. These tests are typically used for diagnosis of PROM, whereas their utility for prediction of preterm birth has not been validated in either large or randomized clinical trials.
In the largest study, which included 796 patients with signs and symptoms of preterm labor, the sensitivities of PAMG-1 and fFN for spontaneous preterm birth within seven days were 50 percent (3/6) and 67 percent (4/6), respectively, and specificities were 98.4 percent (619/629) and 85.7 percent (539/629), respectively [30]. In a prospective study that compared PAMG-1 with pIGFBP-1 among patients in preterm labor with intact membranes, dilation ≤3 cm, and cervical length 15 to 30 mm, both tests had similar sensitivity (75 to 85 percent) for birth within seven days, but PAMG-1 was more specific (95 versus 77 percent) [32].
DIAGNOSIS — We make the diagnosis of preterm labor based upon clinical criteria of regular painful uterine contractions accompanied by cervical change (dilation and/or effacement). Vaginal bleeding and/or ruptured membranes in this setting increase diagnostic certainty [33]. Because the clinical findings of early labor are poorly predictive of the diagnosis, over-diagnosis is common until labor is well established.
We use the following specific criteria: Uterine contractions (≥4 every 20 minutes or ≥8 in 60 minutes) plus
●Cervical dilation ≥3 cm or
●Cervical length <20 mm on transvaginal ultrasound or
●Cervical length 20 to <30 mm on transvaginal ultrasound and positive fetal fibronectin
The contraction criteria are those used for selecting subjects in research settings. Before the use of ultrasound for measuring cervical length, research studies also required documented cervical change or cervical effacement ≥80 percent or cervical dilation >2 cm. These criteria were chosen because patients who did not meet them were often ultimately diagnosed with false labor and went on to have a late preterm or term birth [34].
APPROACH TO TRIAGE: SINGLETON GESTATIONS
≥34 weeks of gestation — Patients with suspected preterm labor at ≥34 weeks are admitted for observation.
After a period of four to six hours:
●Patients found not to be in labor – Patients without progressive cervical dilation and effacement are discharged, as long as fetal well-being is confirmed (eg, reactive nonstress test) and obstetric complications associated with preterm labor, such as abruption, chorioamnionitis, and rupture of membranes, have been excluded. They are given instruction for follow-up in one to two weeks and to call sooner if experiencing additional signs or symptoms of preterm labor or other pregnancy concerns (eg, bleeding, rupture of membranes, decreased fetal activity). (See "Patient education: Preterm labor (Beyond the Basics)".)
●Patients found to be in labor – Patients with progressive cervical dilation and effacement are in labor and managed accordingly. (See "Labor and delivery: Management of the normal first stage", section on 'Management of the first stage of labor'.)
The 34th week of gestation is the threshold at which perinatal morbidity and mortality are generally considered to be too low to justify the potential maternal and fetal complications and costs associated with inhibition of preterm labor, which only results in short term delay in birth (see "Inhibition of acute preterm labor", section on 'Lower and upper gestational age limits').
We typically do not administer antenatal corticosteroids after 34 weeks of gestation because of the low risk of severe respiratory morbidity at this gestational age and the potential for long-term harm following late exposure; however, this is controversial and others administer corticosteroids in this setting. The risks, benefits, and controversies regarding steroid use after 34 weeks are discussed in detail separately. (See "Antenatal corticosteroid therapy for reduction of neonatal respiratory morbidity and mortality from preterm delivery", section on '34+0 or more weeks'.)
<34 weeks of gestation — Patients with uterine contractions and intact membranes at <34 weeks of gestation are admitted for evaluation.
Cervical dilation ≥3 cm — Cervical dilation ≥3 cm supports the diagnosis of preterm labor. Further diagnostic evaluation with sonographic measurement of cervical length or laboratory assessment of fetal fibronectin (fFN) is not performed because these tests do not enhance diagnostic accuracy in this setting. Management is directed at reducing the morbidity and mortality of preterm birth. (See 'Initial treatment of preterm labor <34 weeks' below.)
Cervical dilation <3 cm — The diagnosis is less clear when cervical dilation is <3 cm. Our approach to diagnosis and treatment in these cases is shown in the algorithm and discussed in the sections below (algorithm 1). The use of cervical length measurement, with fFN in selected cases, is based upon clinical experience and accumulating data on risk of preterm birth according to cervical length on transvaginal ultrasound, in the absence of abruption [2,33,35-39].
Cervical length 20 to <30 mm — Symptomatic patients with cervical dilation <3 cm and cervical length 20 to <30 mm are at increased risk of preterm birth compared with those with longer cervical lengths, but most of these patients do not give birth preterm. Therefore, for this subgroup of patients, we send a cervicovaginal sample for fFN testing (see 'Fetal fibronectin for selected patients' above). We believe that selective testing helps reduce diagnostic uncertainty and, in turn, unnecessary intervention, by identifying the significant proportion of patients in this group who are at low (<5 percent) risk of giving birth within seven days [40]. Since the test is expensive, reducing the number of patients tested by one-third is advantageous [41-43].
●If the fFN test is positive, we begin interventions to reduce morbidity associated with preterm birth (see 'Initial treatment of preterm labor <34 weeks' below).
●If the fFN test is negative, we discharge the patient after 6 to 12 hours of observation, given its high negative predictive value (98 to 100 percent for birth within 7 or 14 days [44]) [13].
Use of sonographic cervical length and fFN determinations to differentiate true labor from false labor in preterm symptomatic patients is supported by the Society for Maternal-Fetal Medicine [45], although high quality evidence of efficacy is not available.
Cervical length <20 mm — Symptomatic patients with cervical length <20 mm are at high risk (>25 percent) of giving birth within seven days; the addition of fFN testing does not significantly improve the predictive value of cervical length measurement alone [40-42,46,47]. Therefore, we do not send their cervicovaginal samples to the laboratory for fFN testing and we begin interventions to reduce morbidity associated with preterm birth. (See 'Initial treatment of preterm labor <34 weeks' below.)
Cervical length ≥30 mm — Approximately 50 percent of patients with symptoms of preterm labor have a transvaginal ultrasound cervical length ≥30 mm [36]. These patients are at low risk (<5 percent) of giving birth within seven days, regardless of fFN result; the addition of fFN testing does not significantly improve the predictive value of cervical length measurement alone [40,41,46,47]. Therefore, we do not send their cervicovaginal samples to the laboratory for fFN testing.
After an observation period of four to six hours, patients without progressive cervical dilation and effacement are discharged, as long as fetal well-being is confirmed (eg, reactive nonstress test) and obstetric complications associated with preterm labor, such as abruption, chorioamnionitis, and rupture of membranes, have been excluded. We arrange follow-up in one to two weeks and give the patient instructions to call if they experience additional signs or symptoms of preterm labor or have other pregnancy concerns (eg, bleeding, rupture of membranes, decreased fetal activity). (See "Patient education: Preterm labor (Beyond the Basics)".)
APPROACH TO TRIAGE: TWIN GESTATIONS — The prediction of preterm birth based on cervical length measurement is somewhat different for twin pregnancies, which necessitates some changes in triage criteria. The optimal cervical length threshold appears to be higher due to the higher baseline risk for preterm birth in twins compared with singletons; however, less data are available for establishing appropriate thresholds [48,49].
≥34 weeks of gestation — Triage is the same as for singletons. (See '≥34 weeks of gestation' above.)
<34 weeks of gestation — For twin pregnancies <34 weeks with uterine contractions and intact membranes:
●Cervical dilation ≥3 cm – Cervical dilation ≥3 cm supports the diagnosis of preterm labor; further diagnostic evaluation with sonographic measurement of cervical length or laboratory assessment of fetal fibronectin (fFN) does not enhance diagnostic accuracy. Treatment of preterm labor is initiated. (See 'Initial treatment of preterm labor <34 weeks' below.)
●Cervical dilation <3 cm – The diagnosis of preterm labor is less clear with cervical dilation <3 cm, so a transvaginal ultrasound measurement of cervical length is obtained.
•Cervical length >35 mm – Patients with cervical length >35 mm and no cervical change on digital examination after a four- to six-hour period of observation are at low risk for preterm birth, and can be discharged home, as long as fetal well-being is confirmed, maternal status is stable, and there are no additional maternal concerns.
•Cervical length <25 mm – Patients with cervical length <25 mm are at high risk of preterm birth; therefore, we begin interventions to reduce morbidity associated with preterm birth. (See 'Initial treatment of preterm labor <34 weeks' below.)
•Cervical length 25 to 35 mm – Patients with cervical length 25 to 35 mm on transvaginal ultrasound examination undergo fFN testing. If the test is positive, we begin interventions to reduce morbidity associated with preterm birth (see 'Initial treatment of preterm labor <34 weeks' below). If the test is negative, we discharge the patient after a 6- to 12-hour period of observation.
INITIAL TREATMENT OF PRETERM LABOR <34 WEEKS — We hospitalize patients diagnosed with preterm labor <34 weeks of gestation and initiate the following treatments, in general agreement with recommendations from the American College of Obstetricians and Gynecologists [50]:
●Antenatal corticosteroids – A course of betamethasone or dexamethasone to reduce neonatal morbidity and mortality associated with preterm birth. A single rescue course of antenatal steroids is indicated for pregnancies <34+0 weeks of gestation that are at high risk of preterm delivery within the next seven days and in which the prior course of ACS was administered more than 14 days previously [51]. (See "Antenatal corticosteroid therapy for reduction of neonatal respiratory morbidity and mortality from preterm delivery".)
●Tocolytics – Tocolytic drugs for up to 48 hours to delay birth so that betamethasone or dexamethasone given to the mother can achieve its maximum fetal effect. Inhibition of acute preterm labor and management of pregnancies after successful inhibition are reviewed separately. (See "Inhibition of acute preterm labor" and "Management of pregnancy after resolution of an episode of acute idiopathic preterm labor".)
●GBS prophylaxis – Antibiotics for prophylaxis against early-onset neonatal group B streptococcal (GBS) infection. (See "Prevention of early-onset group B streptococcal disease in neonates", section on 'Special populations'.)
●Neuroprotection – Magnesium sulfate for pregnancies <32 weeks of gestation. In utero exposure to magnesium sulfate provides neuroprotection against cerebral palsy and other types of severe motor dysfunction in offspring born preterm. (See "Neuroprotective effects of in utero exposure to magnesium sulfate".)
Antibiotic therapy has no role in the treatment of acute preterm labor in the absence of a documented infection or GBS prophylaxis [52]. (See "Inhibition of acute preterm labor", section on 'Antibiotic therapy'.)
Progesterone supplementation has no role in the treatment of acute preterm labor. (See "Progesterone supplementation to reduce the risk of spontaneous preterm labor and birth", section on 'Threatened or established preterm labor'.)
OUTCOME
●Overall frequency of preterm birth among patients with suspected preterm labor – Tocolytic therapy is more effective than placebo for delaying birth for 48 hours in randomized trials; however, even when tocolytics are not administered, approximately 50 percent of patients diagnosed with preterm labor give birth at term [53]. (See "Inhibition of acute preterm labor", section on 'Efficacy'.)
●Long-term maternal outcome after giving birth preterm – Mothers who give birth preterm are at risk for recurrent preterm birth. (See "Preterm birth: Risk factors, interventions for risk reduction, and maternal prognosis", section on 'History of spontaneous preterm birth'.)
They also appear to be at increased risk for cardiovascular morbidity and mortality years after the birth. (See "Preterm birth: Risk factors, interventions for risk reduction, and maternal prognosis", section on 'Long-term maternal consequences'.)
●Pediatric outcome after preterm birth – Newborn outcomes of preterm birth are reviewed in the following topics.
•(See "Short-term complications of the preterm infant".)
•(See "Preterm birth: Definitions of prematurity, epidemiology, and risk factors for infant mortality".)
•(See "Late preterm infants".)
•(See "Long-term outcome of the preterm infant".)
•(See "Long-term neurodevelopmental impairment in infants born preterm: Epidemiology and risk factors".)
●Pediatric outcome after suspected preterm labor – Whether a history of suspected preterm labor is associated with adverse neonatal outcome in patients who go on to have term births is controversial. These patients may have underlying pathology, such as subclinical intra-amniotic inflammation, that may adversely affect fetal growth or development even though they go on to have a term birth [54-58].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Preterm labor and birth".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Preterm labor (The Basics)" and "Patient education: How to tell when labor starts (The Basics)")
●Beyond the Basics topics (see "Patient education: Preterm labor (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Signs and symptoms of preterm labor – Early signs and symptoms of both preterm and term labor are nonspecific and include: menstrual-like cramping; mild, irregular contractions; low back ache; pressure sensation in the vagina; vaginal discharge of mucus, which may be clear, pink, or slightly bloody (ie, mucus plug, bloody show). (See 'Clinical findings' above.)
●Diagnosis of preterm labor in singleton pregnancies – The diagnosis of preterm labor is based on presence of regular painful uterine contractions accompanied by cervical dilation and/or effacement. We use the following specific criteria for diagnosis: Uterine contractions (≥4 every 20 minutes or ≥8 in 60 minutes) and (see 'Diagnosis' above):
•Cervical dilation ≥3 cm or
•Cervical length <20 mm on transvaginal ultrasound or
•Cervical length 20 to <30 mm on transvaginal ultrasound and positive fetal fibronectin (fFN)
●Management of suspected preterm labor in singleton pregnancies – The 34th week of gestation is the threshold at which perinatal morbidity and mortality are too low to justify the potential maternal and fetal complications and costs associated with inhibition of preterm labor, which only results in short-term delay in birth. (See '≥34 weeks of gestation' above.)
•For pregnancies ≥34 weeks of gestation, patients without progressive cervical dilation and effacement after an observation period of four to six hours can be discharged to home, as long as fetal well-being is confirmed and obstetric complications associated with preterm labor, such as abruption, chorioamnionitis, and membrane rupture, have been excluded. Patients in preterm labor are admitted to give birth. (See '≥34 weeks of gestation' above.)
•For pregnancies <34 weeks and cervical dilation ≥3 cm, we administer tocolytic drugs for up to 48 hours, antibiotics for group B streptococcal chemoprophylaxis (when appropriate), and antenatal betamethasone. Magnesium sulfate is administered for neuroprotection to pregnancies <32 weeks of gestation. (See 'Initial treatment of preterm labor <34 weeks' above.)
•For pregnancies <34 weeks of gestation and cervical dilation <3 cm, transvaginal ultrasound measurement of cervical length and laboratory analysis of cervicovaginal fFN level help to support or exclude the diagnosis of preterm labor, as described in the algorithm (algorithm 1). For patients diagnosed with preterm labor, we administer tocolytic drugs for up to 48 hours, antibiotics for group B streptococcal chemoprophylaxis (when appropriate), and antenatal betamethasone. Magnesium sulfate is administered for neuroprotection to pregnancies <32 weeks of gestation. (See '<34 weeks of gestation' above.)
●Diagnosis and management in twin pregnancies –The diagnosis of preterm labor in twin pregnancies is based on the same uterine contraction criteria as for singleton pregnancies, and management of preterm labor in twin gestations ≥34 weeks of gestation or <34 weeks with cervical dilation ≥3 cm is also similar to that for singletons, but cervical length criteria for triage of twin pregnancies <34 weeks with cervical dilation <3 cm is different. (See 'Approach to triage: Twin gestations' above.)
•For twin pregnancies <34 weeks and cervical dilation <3 cm, transvaginal ultrasound measurement of cervical length and laboratory analysis of cervicovaginal fFN level help to support or exclude the diagnosis of preterm labor:
-Cervical length >35 mm and no cervical change on digital examination after a four- to six-hour period of observation – Low risk for preterm birth: discharge.
-Cervical length <25 mm – High risk of preterm birth: initiate interventions to reduce morbidity associated with preterm birth.
-Cervical length 25 to 35 mm – fFN testing. If positive, initiate interventions to reduce morbidity associated with preterm birth. If negative, discharge after a 6- to 12-hour period of observation.
