Labor denotes the sequence of physiologic occurrences that result in a fetus being transported from the uterus through the birth canal.
DESCRIPTION 
- Labor brings about changes in the cervix to allow passage of fetus through birth canal
- Synchronous, coordinated contractions of the uterus
- Contractions progress in magnitude, duration, and frequency to produce dilation of the cervix and ultimate delivery
- Labor is divided into 3 stages:
- Stage 1 (cervical stage): From onset of uterine contractions to full dilation of cervix
- Stage 1 is further divided into latent and active phases:
- In the latent phase, uterine contraction with little change in cervical dilation or effacement; contractions are mild, short (< 45 sec), and irregular
- This is followed by the active phase, which begins around time of cervical dilation of 3–4 cm; contractions are strong, regular (every 2–3 min), and last longer (> 45 sec)
- Stage 2: From onset of complete cervical dilation to time of delivery of infant
- Stage 3: From time of delivery of baby to time of placental delivery
- Total duration of labor varies with each woman
- Generally, lengths of 1st and 2nd stages of labor are significantly longer for nulliparous woman:
- Nulliparous: Mean length for 1st stage of labor is 14.4 hr and for 2nd stage of labor is 1 hr
- Parous: Mean length of 1st stage of labor is 7.7 hr and for 2nd stage of labor is 0.2 hr
- Length of 2nd stage of labor is greatly influenced by "3 Ps":
- Passenger (infant size and presentation)
- Passageway (size of bony pelvis and soft tissues)
- Powers (uterine contractions)
- Problems with any of these 3 Ps can cause abnormal progression of labor:
- Fetal malposition, uterine dysfunction, cephalopelvic disproportion
- False labor (Braxton Hicks contractions):
- Irregular, nonsynchronous contractions of uterus several weeks to days before onset of true labor, and do not cause cervical dilation
ETIOLOGY
- Premature labor occurs in 8–10% of pregnancies.
- 30–40% of premature labor is caused by uterine, cervical, or urinary tract infections
- Premature rupture of membranes is defined as rupture of amniotic/chorionic membranes at least 2 hr before onset of labor in patient before 37 wk gestation:
- This occurs in only 3% of pregnancies but accounts for 30–40% of all premature births
[Outline]
SIGNS AND SYMPTOMS
- Symptoms of labor:
- Preterm labor is of sufficient frequency and intensity to bring about changes in dilation or effacement of cervix before 37 wk
- Labor is not associated with vaginal bleeding:
- Patients with 3rd-trimester abdominal pain or vaginal bleeding should raise suspicion of placenta previa or placental abruption
- Sudden release of clear fluid from vagina or feeling of constant perineal wetness can represent rupture of membranes:
- This is not always associated with labor but often leads to onset of labor
History
- Gestational age
- Prenatal care
- Previous pregnancies:
- Recent infections
Physical Exam
- Assess fundal height:
- Centimeters from pubic bone to top of uterus
- Correlates with number of weeks after 2nd trimester
- Can help determine gestational age if unknown
- Sterile pelvic exam to assess cervical dilation and effacement
ALERT
Do not perform a pelvic exam if vaginal bleeding is present.
ESSENTIAL WORKUP
- Patients presenting in possible labor should have immediate sterile pelvic exam to assess dilation, effacement of cervix, and possibility of imminent delivery.
- Bimanual pelvic exam should NOT be done in 3rd-trimester patient with vaginal bleeding until US can be done to assess for placenta previa or placental abruption.
- Patients with suspected rupture of membranes should have sterile speculum exam with visual exam of cervix and collection of fluid from vaginal area
- Suggestive of rupture of membranes:
- Presence of ferning when fluid is allowed to dry on a slide
- Presence of pooling of fluid in vagina
- Change of color of litmus paper from yellow to blue
- Patients with preterm labor and cervical changes should have urinalysis with culture and cervical cultures
- Fetal monitoring should be initiated
DIAGNOSIS TESTS & INTERPRETATION
Lab
- If patient is in labor, CBC, type, and screen should be sent.
- Urinalysis for proteinuria
- In patients with no prenatal care, obtain Rh factor and antibody screen.
- Cervical cultures and urine culture in patients with preterm labor
Imaging
- Not generally needed
- 3rd-trimester patients with abdominal pain and vaginal bleeding should have emergent US to evaluate for placenta previa or abruption.
DIFFERENTIAL DIAGNOSIS
- Braxton Hicks contractions (false labor) are irregular uterine contractions without associated cervical changes:
- Contractions can be every 10–20 min
- Round uterine ligament pain, musculoskeletal back pain
- Other common causes of abdominal pain, such as appendicitis, ovarian cyst, diverticulitis, nephrolithiasis, UTI
[Outline]
PRE-HOSPITAL
- Emergency medical services personnel should place patients in labor on oxygen and in left lateral recumbent position to maximize delivery of oxygen to uterus
- Maternal transport of high-risk obstetric patients before delivery results in improved outcomes instead of transfer of neonate after delivery
- Air transport of high-risk obstetric patients has been shown to be beneficial and cost effective
- Patients in labor who are transported by aircraft should have high-flow oxygen available in the event of cabin decompression at high altitudes
INITIAL STABILIZATION/THERAPY
If delivery is imminent (presenting part visible), prepare for immediate vaginal delivery in ED (see "Delivery, uncomplicated")
ED TREATMENT/PROCEDURES
- Unless delivery is imminent, patient should be sent directly to the labor and delivery (L&D) unit
- If transport to L&D will be delayed, or if transfer to another facility is necessary, these steps should be taken:
- Consider IV antibiotics for unknown group B Streptococcus status
- IV hydration with 1 L NS or 5% dextrose in lactated Ringer over 30–60 min
- Maternal monitoring
- Fetal monitoring
- If labor needs to be arrested (premature fetus), begin a tocolytic such as β-agonist terbutaline or magnesium sulfate:
- Magnesium toxicity is suggested by loss of deep tendon reflexes
- High doses of magnesium can cause cardiac dysrhythmias and respiratory depression.
MEDICATION
- Magnesium sulfate: 4–6 g IV over 30 min, followed by 2–6 g/hr
- Terbutaline: 0.25 mg SC; may repeat same dose in 30 min
ALERT
Consider antibiotic prophylaxis for patients with history of cardiac lesions.
[Outline]
DISPOSITION
Admission Criteria
- All patients in labor who are not at risk for imminent delivery should be admitted to L&D
- Preterm patients in labor demand immediate obstetric consultation and should be admitted to L&D for further treatment
Discharge Criteria
Patients with false labor may be discharged only after obstetric consultation, confirmation of fetal well-being, and close follow-up is arranged:
- False labor may progress to true labor
- Berghella V, Baxter JK, Chauhan SP. Evidence-based labor and delivery management. Am J Obstet Gynecol. 2008;199:445–454.
- DeCherney A, Nathan L, Goodwin TM, et al., eds. Current Diagnosis and Treatment, Obstetrics and Gynecology. 10th ed. New York, NY: McGraw-Hill; 2007.
- Liao JB, Buhimschi CS, Norwitz ER. Normal labor: Mechanism and duration. Obstet Gynecol Clin North Am. 2005;32:145–164.
- Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: Guidelines from the American Heart Association: A guideline from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group. Circulation. 2007;116:1736–1754.
- Wolfson AB, Hendey GW, Ling LJ, et al., eds. Harwood Nuss' Clinical Practice of Emergency Medicine. 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2010.
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