Objective To determine whether oral bacteria are found in the amniotic cavity.

Design Laboratory based analysis of clinical samples.

Setting Royal London Hospital, Whitechapel.

Population Forty-eight women attending for elective caesarean section.

Methods Dental plaque, a high vaginal swab, amniotic fluid and chorioamnion tissue were taken from women with intact membranes.

Main outcome measures Samples were investigated using culture and microscopy for the presence of micro-organisms. Amniotic fluid was analysed by polymerase chain reaction (PCR) for the presence of the ubiquitous 16S rRNA gene specific to most eubacteria. Samples were analysed using PCR genus and species specific primers directed to bacterial taxa found as part of the normal oral microflora (Streptococcus spp. and Fusobacterium nucleatum). Levels of prostaglandin E2 and cytokines were measured in amniotic fluid.

Results Amniotic fluid was positive for universal bacteria PCR, Streptococcus spp. PCR and F. nucleatum PCR in 34/48, 20/48 and 7/48 of cases, respectively. Streptococcus spp. and F. nucleatum were cultured from the dental plaque, vagina and amniotic fluid of 48/48, 14/48, 0/48 and 29/48, 6/48, 0/48 subjects, respectively. A significant association was found between detection of microbial DNA (universal and F. nucletum) and complications in previous pregnancies including miscarriage, intrauterine death, neonatal death, preterm delivery and premature rupture of membranes (P < 0.05 and P < 0.01, respectively). Prostaglandin E2 and cytokine levels, with the exception of IL-1α, were not significantly different between women with and without evidence of infection.

Conclusions The results indicate that Streptococcus spp. and F. nucleatum in the amniotic fluid may have an oral origin.