Preterm labor is defined as regular uterine contractions and cervical changes before 37 weeks' gestation. Preterm birth is defined as live birth between 20 0/7 weeks and 36 6/7 weeks' gestation. Risk factors for preterm labor include a previous preterm birth, a short cervical length during pregnancy, and multiple gestations. Diagnosis is usually based on the presence of regular contractions, cervical effacement, and/or . The risk of impending delivery may be assessed by cervical length ultrasonography and fetal fibronectin test. Management depends on gestational age and can include tocolysis, antenatal steroids to improve fetal lung maturity, and magnesium sulfate for fetal neuroprotection. Tocolytics may be used for short-term prolongation of pregnancy to allow time for steroids and magnesium sulfate to take effect and for transportation to an appropriate hospital. Fetal complications of preterm birth include intraventricular hemorrhage, neonatal respiratory distress syndrome, and necrotizing enterocolitis. Strategies for prevention of preterm birth include reduction in modifiable risk factors, screening for short cervical length, and and short cervical length (e.g., with progesterone supplementation).
- Preterm labor: regular uterine contractions with cervical effacement, dilation, or both before 37 weeks' gestation 
- Preterm birth
- Complications of preterm birth are the leading cause of death in children < 5 years of age worldwide. 
- About half of patients who deliver prematurely are diagnosed with preterm labor. 
- Preterm birth rate in the US: ∼ 12% of all live births 
- African-American women are 50% more likely to give birth prematurely compared to white women.
Epidemiological data refers to the US, unless otherwise specified.
- History of preterm birth (greatest risk factor)
- History of cervical surgery (e.g., conization)
- Short cervical length
- Preterm premature rupture of membranes (PPROM)
Antepartum hemorrhage caused by:
- Uterine anomalies (e.g., anomalies of Mullerian duct fusion, uterine fibroids)
- Black individuals of non-Hispanic origin 
- Congenital abnormalities of the fetus 
- Maternal and fetal conditions
- Lifestyle and environmental factors
The diagnosis of preterm labor is made clinically based on preterm contractions and cervical changes. The presence of risk factors for preterm labor can help establish the diagnosis. Fetal fibronectin levels and cervical length measurements can help assess the risk of impending delivery.
Initial evaluation 
- Evaluate for .
- Determine gestational age.
- Perform sterile speculum examination.
- Perform .
Laboratory studies 
- Cervicovaginal fetal fibronectin (fFN) test
- To rule out infections:
- Transvaginal ultrasound: Cervical length > 3 cm indicates a low likelihood of delivery within 14 days. 
- Obstetric ultrasound
- All patients < 37 weeks' gestation
- 34 0/7 to 36 6/7 weeks' gestation: Proceed with .
- < 34 weeks' gestation
- < 32 weeks' gestation: : Consider magnesium sulfate for fetal neuroprotection.
Activity restriction, including bed rest, is not routinely recommended and may result in adverse outcomes. 
- Definition: administration of tocolytics to inhibit uterine contractions 
- Goal: prolonging pregnancy to allow for induction of fetal lung maturity and/or transfer to another medical center, if necessary
- Duration: up to 48 hours
|Medication||Maternal adverse effects||Fetal adverse effects|
|Nifedipine (calcium channel blocker)|| |
|Indomethacin (NSAID)|| |
|Terbutaline (beta-2 adrenergic agonist)|
|Magnesium sulfate|| |
Induction of fetal lung maturity 
- Definition: administration of antenatal steroids to promote the production of surfactant and thereby improve neonatal survival and fetal lung maturity
- Options (off-label use)
- Definition: administration of antenatal magnesium sulfate to reduce the risk and severity of neurological disorders (e.g., cerebral palsy) 
- Indication: preterm labor at < 32 weeks' gestation 
- Dosing: Follow local protocols. 
- Determine gestational age.
- Sterile speculum examination to evaluate cervix and exclude PPROM
- Rule out infections: urinalysis and culture, , (if indicated)
- Consider and cervical length measurement.
- Consult OB/GYN and/or consider transfer to an appropriate facility.
- , if indicated
- 34 0/7 to 36 6/7 weeks' gestation: Proceed with normal labor and delivery.
- < 34 weeks' gestation
- < 32 weeks' gestation: Consider .
Pulmonary and cardiovascular
Periventricular leukomalacia (PVL)
- Definition: symmetrical, periventricular injury of cerebral white matter (necrosis and cystic formation) caused by ischemia and/or infection
- Epidemiology: mainly affects premature infants
- Clinical features: features of spastic cerebral palsy, intellectual impairment, and visual disturbances
- Diagnostics: brain imaging using ultrasound, cranial CT, or MRI
Intraventricular hemorrhage (IVH) 
- Definition: Bleeding into the ventricles from the germinal matrix, a highly vascularized region within the subventricular zone of the brain from which cells migrate out during brain development.
- Etiology: associated with a number of risk factors
- Immaturity of the basal lamina and lack of astrocytic glial fibrillary acidic protein within the germinal matrix leads to abnormal cerebral autoregulation.
- Alterations in an infant's blood pressure (e.g., during birth, intubation) → failure of cerebral autoregulation to compensate for the change in blood pressure → rupture of and bleeding from vessels in the germinal matrix → rupture of ependyma → blood flows into the ventricles
- Usually occurs within the first days of life (up to day 5)
- Most infants are asymptomatic, but saltatory (for several days) or, more rarely, catastrophic (over minutes to hours) courses are also possible.
- Lethargy, hypotonia, irregular respirations, seizures, bulging anterior fontanelle
- Cranial nerve abnormalities (e.g., pupils react sluggishly to light) and changes in eye movement (e.g., roving eye movements)
- Signs of acute blood loss (e.g., anemia, tachycardia)
Cranial ultrasound: allows grading of IVH based upon the location and extent to assess severity 
- Grade I: bleeding confined to germinal matrix and ≤ 10% of the ventricular area
- Grade II: 10–50% of the lateral ventricle volume occupied by germinal matrix and IVH
- Grade III: > 50% of the lateral ventricle volume occupied by germinal matrix and IVH, ventricular distortion
- Periventricular hemorrhagic infarction: hemorrhagic infarction in periventricular white matter ipsilateral to IVH
- Since most patients are asymptomatic, screening ultrasounds are routinely performed in infants with a birth weight < 1500 g and delivery before 30 weeks' gestation. 
- Cranial ultrasound: allows grading of IVH based upon the location and extent to assess severity 
- Hypothermia of prematurity 
- Apnea, bradycardia
- Hypoglycemia, hyperglycemia
Anemia of prematurity
- Definition: impaired ability to produce adequate erythropoietin (EPO)
- Clinical features: usually asymptomatic, possible symptoms include tachycardia, poor weight gain, increased episodes of apnea
- Pathophysiology: onset of breathing and closure of ductus arteriosus → ↑ tissue oxygenation → ↓ erythropoiesis
- Diagnostics: should be suspected in premature infants with low hemoglobin, hematocrit, and reticulocyte count
- Treatment: iron supplementation, blood transfusions (severe cases)
- ROP) (
- NEC) (
- Infection and sepsis (e.g., neonatal sepsis, neonatal pneumonia)
We list the most important complications. The selection is not exhaustive.
Primary prevention 
for all patients, including:
- Screening for infections (see “ ”)
- For singleton pregnancies: , e.g., vaginal progesterone and/or cervical cerclage. 
- The following measures are not recommended due to a lack of efficacy: 
Evaluation for preterm birth.can identify individuals at increased risk for
|Screening for short cervical length |
|Screening modality and interval||Follow-up of abnormal results|
|Singleton pregnancy||History of preterm birth|| |
|No history of preterm birth|| |
|Multiple pregnancy |