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Preterm labor

Last reviewed: 4 Sep 2023
Last updated: 31 May 2023



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
More key diagnostic factors

Other diagnostic factors

  • increased maternal or fetal heart rate
  • nonspecific lower abdominal or back pain
  • fever
  • vaginal bleeding
Other diagnostic factors

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
  • late-stage caesarean section
More risk factors

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
More 1st investigations to order

Investigations to consider

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

Treatment algorithm


threatened preterm labor (TPTL)

preterm premature rupture of membranes (PPROM)

high risk of imminent delivery without PPROM



Andrew H. Shennan, MD, FRCOG

Professor of Obstetrics

King's College London




AHS has received a grant from Hologic to evaluate fetal fibronectin. AHS is an author of several references cited in this topic.

Joanna C. Girling, MA, MRCP, FRCOG

Consultant in Obstetrics and Gynaecology

West Middlesex University Hospital




JCG declares that she has no competing interests.

Peer reviewers

Jo Trinder, MD

Consultant Obstetrician and Gynaecologist

St Michael's Maternity Wing

Bristol Royal Infirmary




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




KD declares that she has no competing interests.

Deidre Lyell, MD

Assistant Professor of Maternal-Fetal Medicine

Stanford University




DL declares that she has no competing interests.

  • Differentials

    • Placental abruption
    • Urinary tract infection (UTI)
    • Ovarian cyst
    More Differentials
  • Guidelines

    • Prediction and prevention of spontaneous preterm birth
    • Practice bulletin no. 217: prelabor rupture of membranes
    More Guidelines
  • Patient leaflets


    Premature labor

    More Patient leaflets
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