Preterm labor

Last reviewed: May 2019

Last updated: April 2018

Summary

Can be caused by various factors and occurs between 24 and 37 weeks' gestation. Spontaneous preterm labor is often associated with infection and inflammation, particularly at early gestations. Only a minority of women who present with preterm contractions progress to actual labor and delivery.

Risk factors include previous preterm labor, cervical surgery, urinary tract infections, and multiple (multifetal) pregnancies. Bleeding and premature rupture of membranes at any gestation is associated with higher rates of preterm delivery.

Early spontaneous birth can be predicted using serial digital examination or transvaginal ultrasound of the cervix. Fetal fibronectin detected in cervico-vaginal secretions can also be used after 22 weeks' gestation. Combining cervical ultrasound and fetal fibronectin gives the best prediction of progression to preterm birth.

Effective prophylactic interventions have not been identified. Cervical cerclage has a limited role in high-risk women, and progesterone therapy may be of benefit. Few lifestyle interventions improve outcome, but cessation of smoking is recommended.

In utero transfer to appropriate neonatal facilities and prenatal corticosteroids reduce perinatal mortality and morbidity. Tocolytic agents are used in some patients to prevent birth in the short term, in order to achieve in utero transfer and allow corticosteroid administration. Longer-term use of tocolysis is not established as an effective intervention.

Definition

There is no internationally recognized definition of preterm labor. Preterm birth occurs between 24 and 37 weeks' gestation. In two-thirds of cases, it occurs following spontaneous onset of labor. Only a minority of women who present with preterm contractions known as threatened preterm labor (TPTL) progress to actual labor and delivery. The remainder of preterm birth is due to iatrogenic delivery, most commonly because of preeclampsia and intrauterine growth restriction. Preterm premature rupture of membranes (PPROM) is defined as the rupture of membranes at <37 weeks' gestation and prior to the onset of labor. This topic will focus on the management of spontaneous preterm labor that may follow TPTL or PPROM.

History and exam

Key diagnostic factors

history of preterm labor, cervical trauma, or induced abortion
multifetal pregnancy and presence of maternal infection
uterine contractions
preterm premature rupture of membranes (PPROM)
advanced cervical dilation
cervical length <2 cm

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Other diagnostic factors

increased maternal or fetal heart rate
nonspecific lower abdominal or back pain
fever
vaginal bleeding

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Risk factors

previous preterm labor
previous cervical trauma
previous induced abortion
maternal infections
multifetal pregnancies
short cervical length
positive fetal fibronectin test
preterm premature rupture of membranes (PPROM)
fetal abnormalities
smoking
body mass index (BMI) <19 kg/m^2
social factors and ethnicity
polyhydramnios
domestic violence
poor dental hygiene

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Diagnostic investigations

1st investigations to order

nonstress cardiotocogram
tocography
transvaginal ultrasound of the cervix
cervico-vaginal swab for fetal fibronectin
CBC
CRP
urine dipstick
urine microscopy, culture, and sensitivity
high vaginal/rectal culture

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Investigations to consider

nitrazine test
microscopy of vaginal fluid
Kleihauer blood test
urine toxicology screen
IGFBP-1 (insulin-like growth factor binding protein-1) test
placental alpha microglobulin-1 (PAMG-1)

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Treatment algorithm

ACUTE

threatened preterm labor (TPTL)

preterm premature rupture of membranes (PPROM)

high risk of imminent delivery without PPROM

Contributors

Authors VIEW ALL 

Andrew H. Shennan, MD, FRCOG

Professor of Obstetrics

King's College London

London

Disclosures

AHS gives educational talks financially supported by Hologic and is UK chief investigator for a tocolysis trial sponsored by GlaxoSmithKline. AHS is an author of a number of references cited in this monograph.

Joanna C. Girling, MA, MRCP, FRCOG

Consultant in Obstetrics and Gynaecology

West Middlesex University Hospital

London

Disclosures

JCG declares that she has no competing interests.

Peer reviewers VIEW ALL 

Jo Trinder, MD

Consultant Obstetrician and Gynaecologist

St Michael's Maternity Wing

Bristol Royal Infirmary

Bristol

Disclosures

JT is the primary author of one randomized controlled trial cited in this topic. This trial was funded by an NHS Research and Development Grant and a donation from Exelgyn, the manufacturer of misoprostol. JT has accepted honoraria for speaking to groups of midwives and doctors about miscarriage management.

Kirsty Dundas, MBChB, DCH, FRCOG

Consultant Obstetrician and Gynaecologist

Royal Infirmary of Edinburgh

Honorary Senior Lecturer

University of Edinburgh

Edinburgh

Disclosures

KD declares that she has no competing interests.

Deidre Lyell, MD

Assistant Professor of Maternal-Fetal Medicine

Stanford University

Stanford

Disclosures

DL declares that she has no competing interests.

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Preterm labor

Summary

Definition

History and exam

Key diagnostic factors

Other diagnostic factors

Risk factors

Diagnostic investigations

1st investigations to order

Investigations to consider

Treatment algorithm

threatened preterm labor (TPTL)

preterm premature rupture of membranes (PPROM)

high risk of imminent delivery without PPROM

Contributors

Authors VIEW ALL 

Andrew H. Shennan, MD, FRCOG

Disclosures

Joanna C. Girling, MA, MRCP, FRCOG

Disclosures

Peer reviewers VIEW ALL 

Jo Trinder, MD

Disclosures

Kirsty Dundas, MBChB, DCH, FRCOG

Disclosures

Deidre Lyell, MD

Disclosures

Differentials

Guidelines

Patient leaflets

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