An intra-uterine contraceptive device of the inflatable type provided with a plurality of protrusions for providing an unimpeded passage of the menstrual flow, such protrusions in one embodiment are wave-like configurations and in other embodiments they are arm-like extensions for providing also a plurality...http://www.google.com.hk/patents/US3933153?utm_source=gb-gplus-share專利 US3933153 - Intra-uterine contraceptive device
