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Severe Pyelonephritis in pregnancy

Key points

  • Pyelonephritis is an infection in one or both kidneys.
  • Urinary tract infection (UTI) has been associated with preterm birth, pyelonephritis and sepsis which are leading causes of maternal and perinatal morbidity and mortality.
  • In the UK, screening for asymptomatic bacteriuria at booking to prevent pyelonephritis is now not recommended by NICE owing to a lack of modern, high quality evidence of benefit.
  • This study will provide evidence to inform future guidance.

Surveillance period

1st October 2022 - 30th September 2023


Pyelonephritis refers to infection of one or both kidneys. UTI has been associated with preterm birth, pyelonephritis(1) and sepsis. Preterm birth is the greatest cause worldwide of perinatal mortality and morbidity, while maternal sepsis arising from UTI is an important cause of maternal morbidity(2). In the 1950s, pyelonephritis was the commonest complication of pregnancy, and work at that time to understand the relationship between asymptomatic bacteriuria and subsequent pyelonephritis led to the development of the urine culture diagnostic thresholds that are still widely in use today(3). These diagnostic thresholds have recently been challenged by a broader understanding of urinary pathology(4), although they remain in common use. In the UK, screening for asymptomatic bacteriuria at booking to prevent pyelonephritis was recommended by NICE until August 2021 when the recommendation was removed owing to poor quality evidence about the benefit. The UK National Screening Committee is now exploring evidence regarding the benefits and harms of such screening. It is imperative to understand more about the modern epidemiology of severe pyelonephritis in pregnancy in the UK in order to inform this decision, and potentially to redirect resources to alternative ways to prevent pyelonephritis and reduce harm. This study will enable us to determine the incidence of severe pyelonephritis in pregnancy in the UK and examine the risk factors, management and outcomes for women and their babies. It is hoped that the study findings will inform future guidance.


To use the UK Obstetric Surveillance System (UKOSS) to describe the incidence of severe pyelonephritis in pregnancy in the UK and examine the risk factors, management and perinatal outcomes following this.

Research questions

  • What is the incidence of severe pyelonephritis requiring admission and IV antibiotics in pregnancy in the UK?
  • How does severe pyelonephritis present in clinical practice?
  • What are the risk factors for severe pyelonephritis in pregnancy (including asymptomatic bacteriuria at the first booking visit, diabetes, immunocompromised, recurrent or chronic UTI, renal tract abnormalities as well as standard demographic and medical risk facotrs)?
  • How is severe pyelonephritis in pregnancy managed in the UK?
  • What are the pregnancy, maternal and neonatal outcomes associated with severe pyelonephritis in pregnancy?

Case definition

All pregnant women with severe pyelonephritis requiring hospital admission and IV antibiotics for at least 48 hours.

Pyelonephritis defined as at least 2 of the following: pyrexia / loin pain / positive urine culture


This study is funded by Chadburn Lectureship funds.

Ethics committee approval

This study has been approved by the London - Brent REC (Ref. Number: 10/H0717/20).

Lead investigator

Jane Currie, UCL EGA Institute for Women's Health.

Sample Data Collection Form

UKOSS Severe Pyelonephritis DCF


  1. Small FM, Vazquez JC. Antibiotics for asymptomatic bacteriuria in pregnancy. Cochrane Database Syst Rev. 2019;2019(11).
  2. Acosta CD, Kurinczuk JJ, Lucas DN, Tuffnell DJ, Sellers S, Knight M, et al. Severe maternal sepsis in the UK, 2011-2012: a national case-control study. PLoS Med. 2014;11(7):e1001672.
  3. Kass EH. Bacteriuria and pyelonephritis of pregnancy. Arch Intern Med. 1960;105:194-8.
  4. Sathiananthamoorthy S, Malone-Lee J, Gill K, Tymon A, Nguyen TK, Gurung S, et al. Reassessment of Routine Midstream Culture in Diagnosis of Urinary Tract Infection. J Clin Microbiol, 2019;57(3).

Updated: Tuesday, 24 October 2023 15:01 (v13)

Contact us

For more information about UKOSS, please view the contact details page