A randomized study of 12-mm and 15.9 mm cannulas in midtrimester abortion by laminaria and vacuum curettage

We evaluated the adequacy of a new large-bore vacuum cannula system for midtrimester abortion by randomly allocating patients to be treated with a standard 12-mm vacuum system or the new 15.9-mm system. Cervical dilataion was accomplished by overnight placement of laminaria tents. Blood loss was similar for the two treatment groups and was significantly greater at gestational ages 17 to 18 weeks than for abortions at 16 weeks or less. Operating time was slightly less in the large-cannula group. When the 12-mm cannula was used beyond 13 weeks' gestation, forceps were usually needed to empty the uterus completely. The large-cannula system was able to empty the uterus through 16 weeks, but at 17 and 18 weeks it offered no advantage over the smaller system and forceps were always needed. Complications were minimal. We caution against forcible cervical dilatation to 16 mm and urge the use of laminaria instead. Our findings, together with published reports of the safety of late dilatations and evacuation, would appear to justify wider clinical trials by experienced investigators.