Amniotic fluid analysis for antimicrobial factors.

The antimicrobial factors in amniotic fluid (AF) were analyzed in 81 women during various periods of gestation. The AF inhibited the growth of E. coli 026 when the phosphate/zinc ratio was less than 200 or iron less than or equal to 1.2 microgram/ml and unbound transferrin was greater than 40%. A heat-stable non-lysozymal phosphate insensitive cationic protein with molecular weight higher than transferrin was also found in inhibitory AF. The antimicrobial properties of AF did not correlate with absolute zinc or lysozyme levels. The AF was non-inhibitory when it contained greater than 60 +/- 5 micrograms/ml of phosphate with phosphate/zinc ratio greater than 200, iron greater than 1.2 microgram/ml and unbound transferrin was less than 40%. Amongst all criteria described, iron (P = 0.002) and unbound transferrin levels (P = 0.0005) were the most reliable and consistent all through pregnancy but others were highly reliable only during the 36th-40th week of gestation. The clinical application of these factors are being investigated.