Is there a critical gestational age in neutrophil superoxide production activity?

We studied superoxide (O2-) production in neutrophils from 78 normal pregnant women at 7 to 39 weeks' gestation to determine whether there is a critical gestational age in O2- production activity of maternal neutrophils. The O2- production was measured by determining the rate of superoxide dismutase-inhibitable reduction of ferricytochrome c at 550 to 540 nm. A scattergram of neutrophil O2- production value versus gestational age was analyzed using the least median of squares regression, leading to a statistical stratification in which the median values of O2- production for outlying and nonoutlying points were 6.60 nmol/10(6) cells and 2.72 nmol/10(6) cells, respectively. All of the outlying points were concentrated at 19 to 22 gestational weeks. There was the significant difference in FMLP-induced O2- production in neutrophils of nonpregnant subjects when incubated with the sera from 10 cases (selected among 60 cases with nonoutlying points) (3.86 +/- 0.77 nmol/10(6) cells) compared with 5 cases with outlying points (5.62 +/- 1.19 nmol/10(6) cells) (P < .05) These results suggest that during the normal course of pregnancy, the production of O2- from the function of circulating neutrophils can be dissociated from such neutrophil functions as adherence, chemotaxis, and phagocytosis.