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Emergency and Acute Medicine – Labor
Basic description
Labor is the sequence of physiologic processes that results in transport of the fetus from the uterus through the birth canal. It is characterized by synchronous, coordinated uterine contractions that progressively increase in strength, duration, and frequency, leading to cervical effacement, dilation, and eventual delivery of the fetus and placenta.
Physiology and stages of labor
Labor produces cervical changes that allow passage of the fetus through the birth canal and is divided into three stages. Stage one extends from the onset of regular uterine contractions to complete cervical dilation and is subdivided into latent and active phases. During the latent phase, contractions are mild, irregular, and short, usually lasting less than 45 seconds, with minimal cervical change. The active phase typically begins at 3–4 cm dilation, with strong, regular contractions occurring every 2–3 minutes and lasting longer than 45 seconds. Stage two spans from complete cervical dilation to delivery of the infant. Stage three begins after delivery of the infant and ends with placental delivery.
The total duration of labor varies among patients. Nulliparous patients generally have longer labor, with an average first stage of 14.4 hours and a second stage of 1 hour. Parous patients have shorter labors, with an average first stage of 7.7 hours and a second stage of 0.2 hours. Progression of the second stage is influenced by the “three Ps”: passenger (fetal size and presentation), passageway (pelvic anatomy and soft tissues), and powers (uterine contractions). Abnormalities in any of these factors may lead to dysfunctional labor.
False labor, or Braxton Hicks contractions, consists of irregular, nonsynchronous uterine contractions occurring days to weeks before true labor and does not result in cervical dilation.
Etiology
Preterm labor occurs in approximately 8–10% of pregnancies. Uterine, cervical, or urinary tract infections account for 30–40% of cases. Premature rupture of membranes, defined as rupture of membranes at least two hours before labor onset in patients under 37 weeks’ gestation, occurs in about 3% of pregnancies but accounts for 30–40% of premature births.
Diagnosis: signs and symptoms
True labor presents with regular uterine contractions occurring at least every five minutes, lasting 30–60 seconds, and associated with progressive cervical dilation or effacement. Pain is typically intermittent, located in the lower abdomen, and may radiate to the lower back. Preterm labor produces these changes before 37 weeks’ gestation. Labor is not associated with vaginal bleeding, and bleeding in the third trimester should prompt concern for placental abruption or placenta previa. Sudden release of clear vaginal fluid or persistent perineal wetness suggests rupture of membranes, which may precede labor.
History and physical examination
Assessment should include gestational age, adequacy of prenatal care, prior obstetric history including cesarean delivery, and recent infections. Fundal height should be measured and correlated with gestational age, particularly when dates are uncertain. A sterile pelvic examination is required to assess cervical dilation and effacement, but digital examination is contraindicated in patients with vaginal bleeding until placental location is confirmed.
Essential workup
Patients with suspected labor require immediate sterile pelvic examination to evaluate cervical status and determine the likelihood of imminent delivery. Suspected rupture of membranes should be evaluated with sterile speculum examination for pooling, ferning, and nitrazine testing. Patients with preterm labor and cervical changes require urinalysis with culture and cervical cultures. Continuous fetal monitoring should be initiated when available. Digital or bimanual pelvic examination should be avoided in third-trimester bleeding until ultrasound excludes placenta previa or abruption.
Diagnostic tests and interpretation
If labor is confirmed, obtain a complete blood count and type and screen. Urinalysis should assess for proteinuria. Patients without prenatal care require Rh factor and antibody screening. Imaging is not routinely required, but emergent ultrasound is indicated in third-trimester patients with abdominal pain and vaginal bleeding to evaluate for placental pathology.
Differential diagnosis
False labor presents with irregular contractions without cervical change. Other considerations include round ligament pain, musculoskeletal back pain, appendicitis, ovarian cysts, diverticulitis, nephrolithiasis, and urinary tract infection.
Treatment and initial management
Prehospital management includes oxygen administration and left lateral positioning to optimize uteroplacental perfusion. Transport of high-risk obstetric patients prior to delivery improves outcomes compared with neonatal transfer after birth. If delivery is imminent, prepare for immediate vaginal delivery in the emergency department. Otherwise, patients should be transferred promptly to the labor and delivery unit.
If transfer is delayed or preterm labor is suspected, initiate maternal and fetal monitoring, provide intravenous hydration, and consider antibiotics for unknown group B Streptococcus status. Tocolysis with agents such as magnesium sulfate or terbutaline may be initiated for preterm labor when appropriate, with careful monitoring for toxicity.
Disposition
All patients in true labor should be admitted to labor and delivery. Preterm labor requires immediate obstetric consultation and admission. Patients with false labor may be discharged only after obstetric evaluation, confirmation of fetal well-being, and arrangement of close follow-up.
Pearls and pitfalls
Vaginal bleeding in labor requires urgent evaluation for placental abruption or previa, and digital pelvic examination must be avoided in these cases. Pelvic examinations in labor should always be sterile. False labor can progress to true labor and requires appropriate counseling and follow-up.
Basic description
Labor is the sequence of physiologic processes that results in transport of the fetus from the uterus through the birth canal. It is characterized by synchronous, coordinated uterine contractions that progressively increase in strength, duration, and frequency, leading to cervical effacement, dilation, and eventual delivery of the fetus and placenta.
Physiology and stages of labor
Labor produces cervical changes that allow passage of the fetus through the birth canal and is divided into three stages. Stage one extends from the onset of regular uterine contractions to complete cervical dilation and is subdivided into latent and active phases. During the latent phase, contractions are mild, irregular, and short, usually lasting less than 45 seconds, with minimal cervical change. The active phase typically begins at 3–4 cm dilation, with strong, regular contractions occurring every 2–3 minutes and lasting longer than 45 seconds. Stage two spans from complete cervical dilation to delivery of the infant. Stage three begins after delivery of the infant and ends with placental delivery.
The total duration of labor varies among patients. Nulliparous patients generally have longer labor, with an average first stage of 14.4 hours and a second stage of 1 hour. Parous patients have shorter labors, with an average first stage of 7.7 hours and a second stage of 0.2 hours. Progression of the second stage is influenced by the “three Ps”: passenger (fetal size and presentation), passageway (pelvic anatomy and soft tissues), and powers (uterine contractions). Abnormalities in any of these factors may lead to dysfunctional labor.
False labor, or Braxton Hicks contractions, consists of irregular, nonsynchronous uterine contractions occurring days to weeks before true labor and does not result in cervical dilation.
Etiology
Preterm labor occurs in approximately 8–10% of pregnancies. Uterine, cervical, or urinary tract infections account for 30–40% of cases. Premature rupture of membranes, defined as rupture of membranes at least two hours before labor onset in patients under 37 weeks’ gestation, occurs in about 3% of pregnancies but accounts for 30–40% of premature births.
Diagnosis: signs and symptoms
True labor presents with regular uterine contractions occurring at least every five minutes, lasting 30–60 seconds, and associated with progressive cervical dilation or effacement. Pain is typically intermittent, located in the lower abdomen, and may radiate to the lower back. Preterm labor produces these changes before 37 weeks’ gestation. Labor is not associated with vaginal bleeding, and bleeding in the third trimester should prompt concern for placental abruption or placenta previa. Sudden release of clear vaginal fluid or persistent perineal wetness suggests rupture of membranes, which may precede labor.
History and physical examination
Assessment should include gestational age, adequacy of prenatal care, prior obstetric history including cesarean delivery, and recent infections. Fundal height should be measured and correlated with gestational age, particularly when dates are uncertain. A sterile pelvic examination is required to assess cervical dilation and effacement, but digital examination is contraindicated in patients with vaginal bleeding until placental location is confirmed.
Essential workup
Patients with suspected labor require immediate sterile pelvic examination to evaluate cervical status and determine the likelihood of imminent delivery. Suspected rupture of membranes should be evaluated with sterile speculum examination for pooling, ferning, and nitrazine testing. Patients with preterm labor and cervical changes require urinalysis with culture and cervical cultures. Continuous fetal monitoring should be initiated when available. Digital or bimanual pelvic examination should be avoided in third-trimester bleeding until ultrasound excludes placenta previa or abruption.
Diagnostic tests and interpretation
If labor is confirmed, obtain a complete blood count and type and screen. Urinalysis should assess for proteinuria. Patients without prenatal care require Rh factor and antibody screening. Imaging is not routinely required, but emergent ultrasound is indicated in third-trimester patients with abdominal pain and vaginal bleeding to evaluate for placental pathology.
Differential diagnosis
False labor presents with irregular contractions without cervical change. Other considerations include round ligament pain, musculoskeletal back pain, appendicitis, ovarian cysts, diverticulitis, nephrolithiasis, and urinary tract infection.
Treatment and initial management
Prehospital management includes oxygen administration and left lateral positioning to optimize uteroplacental perfusion. Transport of high-risk obstetric patients prior to delivery improves outcomes compared with neonatal transfer after birth. If delivery is imminent, prepare for immediate vaginal delivery in the emergency department. Otherwise, patients should be transferred promptly to the labor and delivery unit.
If transfer is delayed or preterm labor is suspected, initiate maternal and fetal monitoring, provide intravenous hydration, and consider antibiotics for unknown group B Streptococcus status. Tocolysis with agents such as magnesium sulfate or terbutaline may be initiated for preterm labor when appropriate, with careful monitoring for toxicity.
Disposition
All patients in true labor should be admitted to labor and delivery. Preterm labor requires immediate obstetric consultation and admission. Patients with false labor may be discharged only after obstetric evaluation, confirmation of fetal well-being, and arrangement of close follow-up.
Pearls and pitfalls
Vaginal bleeding in labor requires urgent evaluation for placental abruption or previa, and digital pelvic examination must be avoided in these cases. Pelvic examinations in labor should always be sterile. False labor can progress to true labor and requires appropriate counseling and follow-up.
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