Prematurity is the leading
cause of perinatal morbidity and mortality. Infection
is thought to be the underlying cause in 30-40% of
cases. Evidence for this comes from the presence of
histologic chorioamnionitis associated with premature
and the identification of microorganisms from the placenta,
of babies delivering prematurely. One such infection, which has been implicated
with premature delivery in case control and cohort studies, is bacterial vaginosis
This is not a distinct microorganism but represents an imbalance in the bacterial
vaginal ecosystem resulting in a reduction in the naturally occurring lactobacilli
and a consequent overgrowth of anaerobes,
Gardnerella vaginalis and mycoplasma.
10-30% of pregnant women
Up to 75% may be asymptomatic (4)
Association with adverse pregnancy outcome
The most recent meta- analysis addressing this showed
the odds ratio for preterm birth in the presence of
maternal BV to be 1.85 (CI 1.62-2.11) (5)
In addition the OR for preterm prelabour rupture of
membranes was1.83 (CI 1.32-1.87) and for low birthweight
babies 1.57 (1.39-2.44).
There are 2 main methods.
Clinical: Amsels criteria requires at least
3 out of the following to be present:
- Homogenous vaginal discharge
- Amine odour on application of discharge to 10%
- vaginal pH>4.5
- Clue cells
This is usually scored using either Nugent or Spiegelís
All methods have fairly good agreement. The presence
of clue cells alone has good predictability but is
subject to intra observer variation. Nugentís criteria
has the best inter centre reliability (6),
although no one method is recommended for obstetric
practice above all others.
A longitudinal study found that BV is unlikely to
develop after 16 weeks gestation. It spontaneously
remits in 50% of positive women at term (7).
One study showed a link between BV and prematurity
if the BV was diagnosed at 16-20 weeks but not if diagnosed
at 24-28 weeks (8).
Metronidazole and clindamycin are both effective treatments.
The oral preparations are recommended in obstetric
practice because of a risk of increased premature deliveries
in two studies using clindamycin cream (9,10) and the
lack of improvement in pregnancy outcome using vaginal
metronidazole preparations (11).
There has been no evidence of teratogenicity in the
trials using either metronidazole or clindamycin.
Is there a benefit for screening and treating in
Both the Cochrane review (11) and a subsequent meta-
analysis (12) found no improvement in adverse pregnancy
outcome after screening and treating asymptomatic pregnant
women in the general population.
High risk women with a previous preterm delivery were
found to benefit from treatment in the Cochrane review.
One study published subsequently found no benefit of
treatment in terms of adverse pregnancy outcome in
this group (13)- however they were screened and treated
twice and were treated on the second time irrespective
of the swab result. They therefore may have been treated
when actually clear of BV. Treatment in the absence
of BV has been associated with adverse pregnancy outcome
(14) and this may be the confounding variable in this
Recommendations for practice
- Women with BV in pregnancy have an increased risk
of preterm birth, preterm prelabour rupture of membranes
and low birth weight
- The current evidence does not support screening
and treating all women for BV in pregnancy.
- There appears to be clinical benefit from screening
and treating those asymptomatic women who have had
a previous preterm birth.
- Treatment should not be given if BV status is negative.
- Treatment should be either oral metronidazole or
- Symptomatic women may also be tested and treated
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KK, Eschenbach DA. A case- control study of chorioamnionitis
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