Bacterial growth inhibition by amniotic fluid. III. Demonstration of the variability of bacterial growth inhibition by amniotic fluid with a new plate-count technique.

The ability of 50 human amniotic fluid samples to inhibit the growth of Escherichia coli was measured with a new semimicro plate-count technique. A range from bacterial growth-sustaining fluid to bactericidal fluid was observed. When the inhibitory capacities of the fluid samples were correlated with gestational age, a progressive increase was obtained with maximum inhibitory capacity at 36 to 40 weeks. All fluid samples obtained before 20 weeks' gestation were capable of supporting bacterial growth. Fluid samples of 36 to 40 weeks' gestation were all bactericidal or bacteriostatic. More variability in inhibitory capacity was seen after 40 weeks, with an over-all loss of inhibition observed.