Increased Release of Cervical Nitric Oxide in Spontaneous Abortion before Clinical Symptoms: A Possible Mechanism for Preabortal Cervical Ripening

Abstract

Nitric oxide (NO) affects cervical ripening. We studied cervical NO release in women with nonviable pregnancy before signs of abortion. Women with missed abortion (n = 56), blighted ovum (n = 36), or tubal pregnancy (n = 7) were selected by means of vaginal ultrasonographic examination from a population seeking early pregnancy termination; 140 women with amenorrhea-matched normal gestation were studied as controls. Cervical fluid samples were assessed for NO metabolites (Nox) by means of Griess reaction. Cervical fluid Nox was more often detectable in women with missed abortion (90%) and blighted ovum (87%) than in the control women (55%; P = 0.01), and Nox levels in women with missed abortion [median, 59.4 mumol/liter; 95% confidence interval (CI), 30.3-81.8] and blighted ovum (25.6 mumol/liter; 95% CI, 14.1-53.0) were 14 and 6 times higher (P < 0.001 and P = 0.002, respectively) than in the control group (4.3 mumol/liter; 95% CI, <3.8 to 6.4). Nox levels in women with tubal pregnancy were normal. In women with nonviable pregnancy, the lower the level of progesterone, expressed as a percentage of that in the control women, the higher (r = -0.69; P < 0.001) the level of cervical fluid Nox, and those with low pretreatment Nox levels failed to abort completely after mifepristone-misoprostol or expectant management more often (P = 0.04) than women with high Nox levels (28% vs. 4%); no such relationship was seen in the control group. Increased preabortal cervical NO release may contribute to cervical ripening and the onset of clinical abortion.