The author of this paper presents own new generation of IUDs, named "Antigrav", patented, and used for 14 years. Proper construction of these IUDs prevents expulsion by the uterus, and protects the uterus against injuries. This report comprise 7 year od study performed in two periods. Four size of the antigravs were used during the study. In the first period od study when applied only two sizes of antigravs-size 2, and 3 in parous women, very great different of Pearl index was obtained. In the case of the bigger size 3 of the antigravs-0.5, and for smaller size 2 of the antigravs-2.5. On the base of such differences results, the author of this paper came to the conclusion that efficacy of an IUD depend on paper selection od IUD to the dimension of the uterine cavity. For fulfill such condition the author performed measurements of the uteri cavities in vivo with a uterometer, and revealed great differences in their dimensions. Consequently the uteri were divided into four groups depending on inner length (depth), and four sizes of antigravs were used. Owing to such action in the second period of study was applied 4 size of antigravs selected to the dimension of the uterine cavity, what decreased Pearl index to 0.8. During 7 years of study none of the antigravs fell out of the uterus. Excluding pregnancies, 4 personal, and two clinical reasons requiring removal of antigravs, no others complications were record.