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Influence of bacterial vaginosis on conception and miscarriage in the first trimester: cohort study

BMJ 1999; 319 doi: https://doi.org/10.1136/bmj.319.7204.220 (Published 24 July 1999) Cite this as: BMJ 1999;319:220
  1. S G Ralph, specialist registrara,
  2. A J Rutherford, clinical directorb,
  3. J D Wilson, consultant physician (jdwilson{at}dunham.freeuk.com)a
  1. a Department of Genitourinary Medicine, General Infirmary at Leeds, Leeds LS1 3EX
  2. b Reproductive Medicine Unit, General Infirmary at Leeds
  1. Correspondence to: J D Wilson
  • Accepted 12 May 1999

Abstract

Objectives: To assess whether bacterial vaginosis affects the rates of conception and miscarriage in the first trimester.

Design: Cohort study.

Setting: Assisted conception unit of a teaching hospital in Leeds.

Participants: 867 consecutive women undergoing in vitro fertilisation.

Interventions: Screening for bacterial vaginosis with a Gram stained vaginal smear before egg collection.

Main outcome measures: The presence of bacterial vaginosis or normal vaginal flora, and the rate of conception and miscarriage in the first trimester.

Results: 190 of 771 (24.6%) women had bacterial vaginosis. No difference in conception rate was found between those women with bacterial vaginosis and those with normal vaginal flora: 61 women (32.1%) and 146 of 493 women (29.6%) respectively (relative risk 1.08, 95% confidence interval 0.85 to 1.39; odds ratio 1.12, 0.77 to 1.64). However, 22 women (31.6%) with bacterial vaginosis who conceived had a significantly increased risk of miscarriage in the first trimester compared with 27 women (18.5%) with normal vaginal flora (crude relative risk 1.95, 1.11 to 3.42; crude odds ratio 2.49, 1.21 to 5.12). This increased risk remained significant after adjustment for factors known to increase the rate of miscarriage: increasing maternal age, smoking, history of three or more miscarriages, no previous live birth, and polycystic ovaries (adjusted relative risk 2.03, 1.09 to 3.78; adjusted odds ratio 2.67, 1.26 to 5.63).

Conclusions: Bacterial vaginosis does not affect conception but is associated with an increased risk of miscarriage in the first trimester in women undergoing in vitro fertilisation, independent of other risk factors.

Key messages

  • Bacterial vaginosis does not affect conception rate

  • Bacterial vaginosis is associated with a two-fold risk of miscarriage in the first trimester

  • The increased miscarriage rate is equivalent to one extra miscarriage for every six pregnant women with bacterial vaginosis

  • The most likely cause of the miscarriages is due to pre-existing endometritis affecting implantation or early embryonic development, which could also affect naturally conceived pregnancies

Footnotes

  • Funding None.

  • Competing interests None declared.

  • Accepted 12 May 1999
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