Preterm labor and birth

Last updated: October 18, 2023

Summarytoggle arrow icon

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 rupture of membranes. 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 management of cervical insufficiency and short cervical length (e.g., with progesterone supplementation).

Definitiontoggle arrow icon

  • Preterm labor: regular uterine contractions with cervical effacement, dilation, or both before 37 weeks' gestation [1]
  • Preterm birth
    • Live birth between 20 0/7 weeks' and 36 6/7 weeks' gestation
    • WHO subcategories [2]
      • Extremely preterm (< 28 weeks)
      • Very preterm (28 to < 32 weeks)
      • Moderate to late preterm (32 to < 37 weeks)

Epidemiologytoggle arrow icon

Epidemiological data refers to the US, unless otherwise specified.

Etiologytoggle arrow icon

The exact mechanisms underlying premature labor are not well understood, but certain risk factors have been identified. [5][6]

Nonmodifiable risk factors

Modifiable risk factors

Clinical featurestoggle arrow icon

To decrease the risk of infection, avoid digital cervical examinations until PPROM has been ruled out. [5][11]

Diagnosticstoggle arrow icon

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 [1][5]

Laboratory studies [1][5]

Ultrasound [5][13]

As cervical length and fetal fibronectin levels each have a low positive predictive value, neither should be used in isolation to assess the risk of preterm delivery. [1]

Treatmenttoggle arrow icon

Approach [1][5]

Activity restriction, including bed rest, is not routinely recommended and may result in adverse outcomes. [1][14]

Tocolysis [1][5][15]


Do not delay labor by administering tocolytics if there is evidence of fetal demise, abruption, eclampsia, or intrauterine infection. [17]

Long-term use of tocolytics does not prevent preterm birth and does not improve neonatal outcomes. [1]


Tocolytics [1][18][19]
Medication Maternal adverse effects Fetal adverse effects
Nifedipine (calcium channel blocker)
  • No known adverse effects
Indomethacin (NSAID)
Terbutaline (beta-2 adrenergic agonist)
Magnesium sulfate
  • Possibly skeletal abnormalities with prolonged use [20]

There are no FDA-approved tocolytic drugs; all agents are used off-label.

Induction of fetal lung maturity [1][21]

Fetal neuroprotection

Antibiotics [1][22]

Acute management checklisttoggle arrow icon

Complicationstoggle arrow icon

Pulmonary and cardiovascular


Periventricular leukomalacia (PVL)

Intraventricular hemorrhage (IVH) [23]



  • Hypothermia of prematurity [26]
    • Definition: impaired ability to produce an adequate body temperature due to a high surface area: volume ratio
    • Clinical features: body temperature < 97.7°F (< 36.5°C), lethargy, cyanosis
    • Treatment: rewarming in an incubator or radiant warmer
  • Apnea, bradycardia
  • Hypoglycemia, hyperglycemia


Morbidity and mortality in preterm infants increase with decreasing birth weight and gestational age.

We list the most important complications. The selection is not exhaustive.

Preventiontoggle arrow icon

Primary prevention [7][27]


Evaluation for short cervical length can identify individuals at increased risk for preterm birth.

Screening for short cervical length [5][7][27]
Screening modality and interval Follow-up of abnormal results
Singleton pregnancy History of preterm birth
No history of preterm birth
Multiple pregnancy [27]

Referencestoggle arrow icon

  1. American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins. Practice Bulletin No. 171: Management of Preterm Labor. Obstetrics & Gynecology. 2016; 128 (4): p.e155-e164.doi: 10.1097/aog.0000000000001711 . | Open in Read by QxMD
  2. Preterm Birth Fact Sheet. Updated: November 1, 2016. Accessed: May 10, 2017.
  3. Reproductive Health - Preterm Birth. Updated: November 10, 2016. Accessed: May 10, 2017.
  4. Carmen Giurgescu, Amelia Banks, Barbara L. Dancy, Kathleen Norr. African American Women's Views of Factors Impacting Preterm Birth. MCN: The American Journal of Maternal/Child Nursing. 2014; 38 (4): p.229-234.doi: 10.1097/nmc.0b013e318293bbbb . | Open in Read by QxMD
  5. Rundell K, Panchal B. Preterm Labor: Prevention and Management. Am Fam Physician. 2017; 95 (6): p.366-372.
  6. Goldenberg RL, Culhane JF, Iams JD, et al. Epidemiology and causes of preterm birth. Lancet. 2008; 371 (9606): p.75-84.doi: 10.1016/s0140-6736(08)60074-4 . | Open in Read by QxMD
  7. ACOG. Prediction and Prevention of Spontaneous Preterm Birth, Practice Bulletin 234. Obstet Gynecol. 2021; 138 (2): p.e65-e90.doi: 10.1097/aog.0000000000004479 . | Open in Read by QxMD
  8. Honein MA, Kirby RS, Meyer RE, et al. The Association Between Major Birth Defects and Preterm Birth. Matern Child Health J. 2008; 13 (2): p.164-175.doi: 10.1007/s10995-008-0348-y . | Open in Read by QxMD
  9. Jafari Kafiabadi M, Sabaghzadeh A, Khabiri SS, et al. Orthopedic Trauma During Pregnancy; a Narrative Review. Arch Acad Emerg Med. 2022; 10 (1): p.e39.doi: 10.22037/aaem.v10i1.1573 . | Open in Read by QxMD
  10. Cavazos-Rehg PA, Krauss MJ, Spitznagel EL, et al. Maternal Age and Risk of Labor and Delivery Complications. Matern Child Health J. 2014; 19 (6): p.1202-1211.doi: 10.1007/s10995-014-1624-7 . | Open in Read by QxMD
  11. Updated Clinical Guidance for the Use of Progesterone Supplementation for the Prevention of Recurrent Preterm Birth. Updated: April 1, 2023. Accessed: July 26, 2023.
  12. Owens DK, Davidson KW, et al. Screening for Bacterial Vaginosis in Pregnant Persons to Prevent Preterm Delivery. JAMA. 2020; 323 (13): p.1286.doi: 10.1001/jama.2020.2684 . | Open in Read by QxMD
  13. AIUM, ACR, ACOG, SMFM, and SRU. AIUM-ACR-ACOG-SMFM-SRU Practice Parameter for the Performance of Standard Diagnostic Obstetric Ultrasound Examinations. J Ultrasound Med. 2018; 37 (11): p.E13-E24.doi: 10.1002/jum.14831 . | Open in Read by QxMD
  14. Owens R. Intraventricular Hemorrhage in the Premature Neonate. Neonatal Network. 2005; 24 (3): p.55-71.doi: 10.1891/0730-0832.24.3.55 . | Open in Read by QxMD
  15. Bassan H. Ultrasonographic Features and Severity Scoring of Periventricular Hemorrhagic Infarction in Relation to Risk Factors and Outcome. Pediatrics. 2006; 117 (6): p.2111-2118.doi: 10.1542/peds.2005-1570 . | Open in Read by QxMD
  16. Hand IL, Shellhaas RA, Milla SS. Routine Neuroimaging of the Preterm Brain. Pediatrics. 2020; 146 (5): p.e2020029082.doi: 10.1542/peds.2020-029082 . | Open in Read by QxMD
  17. Demtse AG, Pfister RE, Nigussie AK, et al. Hypothermia in Preterm Newborns: Impact on Survival. Global Pediatric Health. 2020; 7: p.2333794X2095765.doi: 10.1177/2333794x20957655 . | Open in Read by QxMD
  18. Lauder J, Sciscione A, Biggio J, Osmundson S. Society for Maternal-Fetal Medicine Consult Series #50: The role of activity restriction in obstetric management. Am J Obstet Gynecol. 2020; 223 (2): p.B2-B10.doi: 10.1016/j.ajog.2020.04.031 . | Open in Read by QxMD
  19. Vogel JP, Ramson J, Darmstadt GL, et al. Updated WHO recommendations on antenatal corticosteroids and tocolytic therapy for improving preterm birth outcomes. The Lancet Global Health. 2022; 10 (12): p.e1707-e1708.doi: 10.1016/s2214-109x(22)00434-x . | Open in Read by QxMD
  20. Haas DM, Caldwell DM, Kirkpatrick P, McIntosh JJ, Welton NJ. Tocolytic therapy for preterm delivery: systematic review and network meta-analysis. BMJ. 2012; 345 (oct09 2): p.e6226-e6226.doi: 10.1136/bmj.e6226 . | Open in Read by QxMD
  21. Walls R, Hockberger R, Gausche-Hill M, Erickson TB, Wilcox SR. Rosen's Emergency Medicine 10th edition- Concepts and Clinical Practice E-Book. Elsevier Health Sciences ; 2022
  22. Caritis S. Adverse effects of tocolytic therapy. BJOG. 2005; 112: p.74-78.doi: 10.1111/j.1471-0528.2005.00590.x . | Open in Read by QxMD
  23. Lamont RF, Jørgensen JS. Safety and Efficacy of Tocolytics for the Treatment of Spontaneous Preterm Labour. Curr Pharm Des. 2019; 25 (5): p.577-592.doi: 10.2174/1381612825666190329124214 . | Open in Read by QxMD
  24. Yokoyama K, Takahashi N, Yada Y, et al. Prolonged maternal magnesium administration and bone metabolism in neonates. Early Hum Dev. 2010; 86 (3): p.187-191.doi: 10.1016/j.earlhumdev.2010.02.007 . | Open in Read by QxMD
  25. ACOG. Committee Opinion No. 713: Antenatal Corticosteroid Therapy for Fetal Maturation. Obstetrics & Gynecology. 2017; 130 (2): p.e102-e109.doi: 10.1097/aog.0000000000002237 . | Open in Read by QxMD
  26. Kenyon S, Boulvain M, Neilson JP. Antibiotics for preterm rupture of membranes. Cochrane Database Syst Rev. 2003.doi: 10.1002/14651858.cd001058 . | Open in Read by QxMD
  27. American College of Obstetricians and Gynecologists. Prelabor Rupture of Membranes: ACOG Practice Bulletin, Number 217.. Obstet Gynecol. 2020; 135 (3): p.e80-e97.doi: 10.1097/AOG.0000000000003700 . | Open in Read by QxMD
  28. van Baaren GJ, Vis JY, Wilms FF, et al. Predictive Value of Cervical Length Measurement and Fibronectin Testing in Threatened Preterm Labor. Obstet Gynecol. 2014; 123 (6): p.1185-1192.doi: 10.1097/aog.0000000000000229 . | Open in Read by QxMD
  29. Coutinho CM, Sotiriadis A, Odibo A, et al. ISUOG Practice Guidelines: role of ultrasound in the prediction of spontaneous preterm birth. Ultrasound Obstet Gynecol. 2022; 60 (3): p.435-456.doi: 10.1002/uog.26020 . | Open in Read by QxMD

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