The clinical significance of blood-contaminated midtrimester amniocentesis

In 706 midtrimester amniocenteses, 180 (25.5%) samples yielded blood-stained amniotic fluid (macroscopically and microscopically), 152 (21.5%) contained maternal blood, 28 (3.9%) fetal blood and 8 samples contained both maternal and fetal blood. In the 180 cases of bloody midtrimester amniocentesis, the abortion rate was 6.6% when maternal blood was found and 14.3% when fetal blood was aspirated, compared with 1.7% in controls. The amount of blood drawn did not alter pregnancy outcome. The percentage of blood amniotic fluid in amniocenteses performed before the 16th week of pregnancy was much higher (36.7%) than during and after the 16th week of pregnancy (22%). Midtrimester amniocentesis should therefore be avoided before the 16th week of pregnancy.