Lea’s Shield, approved by the FDA in 2002, is another vaginal barrier device made of silicone rubber. It is intended for use with a spermicide. It is shaped like an elliptical bowl with a central air valve approximately the size of a diaphragm, featuring an anterior loop to assist its removal. The posterior end is thicker and therefore less likely to rotate when in place. It comes in one size; proper fitting requires only that it cover the cervix, sit behind the symphysis, and be comfortable. The shield needs to be inserted prior to each act of intercourse and should not be left in the vagina for longer than 48 hours (53). A prescription is required. Approximately 87% of those responding to a question about their use of the shield stated that they would recommend its use to a friend (51). Of 59 women who used the device with N-9 spermicide, the 6-month pregnancy rate was 15% (54).
The Sponge The Today sponge is a polyurethane dome-shaped device containing nonoxynol-9. It is moistened with water and then inserted high in the vagina to cover the cervix. It combines the advantages of a disposable barrier with spermicide and provides protection for 24 hours. The contraceptive efficacy appears to differ with parity. Nulliparous women are reported to have a perfect use pregnancy rate of 9% per year, whereas parous women have a pregnancy rate of 20% (Table 10.2). Rates with typical use are estimated as 16 per year in nullipara and 32% in multipara (55). A trial comparing the sponge with a vaginal spermicide preparation used alone without barrier showed the sponge had a slightly lower pregnancy rate (56).
Figure 10.4 Copper T380A (ParaGard) intrauterine device.
Worldwide over 15% of married women use intrauterine contraception (57). In the United States, usage is increasing, but the estimates are that only 3.4% of women and only 5.0% of married women use intrauterine contraception (4). Candidacy includes nulliparous women, adolescents, and immunocompromised women. Immediate use postpartum or after a first or second trimester abortion broadened usage. Two IUDs are in use in the United States: the copper T380A (ParaGard) and the levonorgestrel-releasing T (Mirena). The copper T380A has bands of copper on the cross arms of the T in addition to copper wire around the stem, providing a total surface area of 380 mm of copper, almost double the surface area of copper in earlier copper devices (Fig. 10.4). It is approved for up to 10 years of continuous use. The levonorgestrel T (Fig.
10.5) is approved in the United States for 5 years of use, although studies through 7 years of use show no loss of efficacy (58). Both provide safe, long-term contraception with effectiveness equivalent to tubal sterilization.
Mechanism of Action
Intrauterine devices cause the formation of “biologic foam” within the uterine cavity that contains strands of fibrin, phagocytic cells, and proteolytic enzymes. All IUDs stimulate the formation of prostaglandins within the uterus, consistent with both smooth muscle contraction and inﬂammation. Copper IUDs continuously release a small amount of the metal, producing an even greater inﬂammatory response. Scanning electron microscopy studies of the endometrium of women wearing nonmedicated IUDs show alterations in the surface morphology of cells, especially of the microvilli of ciliated cells (59). There are major alterations in the composition of proteins within the uterine cavity and new proteins and proteinase inhibitors are found in washings from the uterus (60). The altered intrauterine environment interferes with sperm passage through the uterus, preventing fertilization.