忘備録
1984年の次の論文によれば、金属製（rigid type）の1つ穴タイプは他の3種（金属製2つ穴、プラスチック製（flexible）1つ穴、プラスチック製2つ穴）と比較して有意に中絶失敗率が高い。
Comparison of Rigid and Flexible Cannulae for Early Abortion without Cervical Dilatation
World Health Organization Task Force on Sequelae of Abortion, Special Programme of Research, Development and Research Training in Human Reproduction
Studies in Family Planning, Volume 15 Number 2 March/April 1984, pp.79-83
