Author:
Adam Z.Barkin
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 s), 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 s)
- 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
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
Diagnostic Tests & Interpretation
Lab
- If patient is in labor:
- 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
- Fetal fibronectin
- Used to evaluate for preterm labor
- Protein that helps keep amniotic sac “glued” to lining of the uterus
- If a positive test, suggests disruption of this adherence and increased risk of preterm labor
- Sent only between weeks 22 and 34 as a swab of cervix
- Usually sent by OB/GYN
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
Prehospital
- Emergency medical services personnel should place patients in labor on oxygen and in left lateral recumbent position to maximize delivery of oxygen to uterus
- May also manually displace uterus to the left
- 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's 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
- In case of hemorrhage, tranexamic acid at 10-15 mg/kg IV over 10 min
ALERT |
| Consider antibiotic prophylaxis for patients with history of cardiac lesions. |
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
- BerghellaV, BaxterJK, ChauhanSP. Evidence-based labor and delivery management . Am J Obstet Gynecol. 2008;199:445-454.
- CaugheyAB. Evidence based management of labor and delivery: What do we still need to know ? Obstet Gynecol Clin North Am. 2017;44(4):xiii-xiv.
- CohenW, FriedmanE. Perils of the new labor management guideline . Am J Obstet Gynecol. 2015;212:420-427.
- MaconesG. Management of Labor and Delivery. 2nd ed.Oxford, UK: John Wiley; 2016.
- MendolaP, LaughonS, MannistoTI, et al. Obstetric complications among US women with asthma . Am J Obstet and Gynecol. 2013;208:127.e1-127.e8.
See Also (Topic, Algorithm, Electronic Media Element)
The authors gratefully acknowledge Jonathan B. Walker for his contribution to the previous edition of this chapter.