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Elevated vaginal pH
and vaginal neutrophils are associated with early preterm birth.
Elevated vaginal pH and neutrophils
are associated strongly with early spontaneous preterm birth.
Simhan HN, Caritis SN, Krohn MA, Hillier SL.
American
Journal of Obstetrics and Gynecology 2003;189:1150-1154.
Summary:
Question
What is the association between vaginal pH >5.0 and vaginal
neutrophils >5 per oil-field with preterm birth?
Design
Gram-stained vaginal smears, examined for the detection of neutrophils and
vaginal pH levels were determined for a prematurity cohort of women at 23
and 26 weeks gestation to establish the relationship between these markers
and early spontaneous preterm birth.
Participants
Subjects from the Vaginal Infections and Prematurity study, a seven-center
cohort comprised of 13,917 women enrolled between 23 and 26 weeks
gestation and followed-up until delivery, were studied. Women were
excluded if they were less than 16 years old, had medical conditions that
were related to prematurity, or taking selected medications. The cohort
included roughly equal numbers of white, African American, and Hispanic
women.
Description of Tests and Diagnostic
Standard
At all study visits, a pelvic examination with a speculum was performed.
Vaginal swabs were obtained for measurement of pH and for preparation of
Gram-stained smears. Neutrophils were counted in five nonconsecutive
fields of the smear that did not have cervical mucus and averaged. Only
areas that had a single layer of epithelial cells were evaluated.
Main Outcome Measures
The association between elevated vaginal pH (>5.0) and
neutrophils (>5 per oil-field) with spontaneous preterm birth was
determined.
Main Results
Vaginal pH >5.0 was present in 2500 (18.0%) and vaginal
neutrophils >5 per oil-field was present in 5751 (41.3%) of the 13,917
women. Both markers were present in 1149 (8.3%) women. The association of
either vaginal pH >5.0, vaginal neutrophils >5 per oil-field,
or both markers with spontaneous preterm birth at various gestational ages
are shown in the table. The strength of the association increased with
earlier gestational age for both markers. The proportion of deliveries
<32 weeks of gestation increased among women with either marker and was
highest among women with both an elevated pH and vaginal neutrophils.
Increased vaginal neutrophils were present in 50.3% of the women with a
sexually transmitted infection (STI) and in 39.1% of women without an STI
(P<0.001). The association between vaginal neutrophils and early
preterm birth before 32 weeks gestation among women without STI was
significant (P=0.002). The mean vaginal pH significantly decreased
with increasing numbers of Lactobacillus morphotypes, which were scored
from zero to 4+ on the Gram-stained smears, suggesting that vaginal pH
reflected the presence of lactobacilli. The combination of elevated
vaginal pH and the presence of vaginal neutrophils had a sensitivity,
specificity, positive predictive value, and negative predictive value of
17.5%, 91.8%, 3.6%, and 91.8%, respectively, for preterm birth at <32
weeks gestation.
Authors' Conclusions
The presence of both microbiologic and
inflammatory changes in the lower genital tract of women at 23 to 26
weeks' gestation identifies women at increased risk of subsequent
spontaneous early preterm birth. The use of either or both vaginal pH and
vaginal neutrophils to predict preterm birth in a clinical setting is not
recommended.
Source of
funding: National Institutes
of Health grant
For correspondence: Hyagriv N. Simhan,
300 Halket St., Pittsburgh, PA 15213. E-mail address: hsimhan@mail.magee.edu.
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