Objective: Our purpose was to evaluate the incidence of asymptomatic amniotic fluid infection.

Study design: One hundred fifty-four amniotic fluid samples obtained at the second trimester between 14 and 27 weeks gestation were studied by Gram stain with bacteriological cultures and detection of mycoplasm species and Chlamydiae trachomatis. Transabdominal amniocentesis for caryotyping were carried out in 151 health patients with intact membranes and without preterm labor or signs of infectious (3 dizygotic twin pregnancies).

Results: One hundred forty-seven complete microbiologic examinations were performed (Gram stain examination white-cell count, quantitative aerobic and anaerobic cultures). Commercial texts for Mycoplasma hominis, Ureaplasma urealyticum and Chlamydiae trachomatis were negative. Three patients had rare microorganisms, coagulase negative staphylococcus (30 and 50 bacteria per ml) and alpha-hemolytic streptococcus (5 x 10(2) bacteria per ml). White cell count on amniotic fluids in 50 cases (32%) was less than 30 per ml.

Conclusion: These findings appear to be in contradiction with recent data, suggesting the existence of intraamniotic infection in the early phase of the second trimester. Our data confirm the need for a cut-off level for white cell count to improve test sensibility.