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Contraception. 1989 Jan;39(1):73-84.

Acceptability of an experimental intracervical device: results of a study controlling for selection bias.

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Department of Obstetrics and Gynecology, University of Texas Health Science Center, San Antonio 78284.


We analyzed baseline and 12-month follow-up interview data from 98 women who had volunteered to use an experimental intracervical device (ICD) and from 155 women who had been randomly assigned to two control groups, the levonorgestrel-releasing intrauterine device (LNG-IUD; N = 86) and the copper Nova-T IUD (N = 69). All participants were clinic patients in Helsinki, Finland. Initial analysis of 12-month discontinuation data indicated that a significantly higher percent of ICD users (22.4) discontinued their device than did either LNG-IUD (7.0) or Nova-T (8.7) users. However, we were no longer able to detect significant differences in discontinuation after controlling for baseline variables that assessed predisposition to be dissatisfied with contraception in general. Adjusted probabilities of discontinuing the ICD, LNG-IUD, and Nova-T were 11.8%, 6.2% and 7.9%, respectively. These data indicate that the ICD is likely to be acceptable to Helsinki clinic patients; moreover, they suggest a definite place for hormonal intrauterine devices in the contraceptive armamentarium. Most importantly, the methodology used here can be generalized to acceptability studies of other contraceptive devices and drugs undergoing Phase I and early Phase II clinical trials (in situations where randomization may not be feasible) in order to identify and control for the bias introduced by nonrandom assignment procedures.


253 women aged 18-38 participated in comparative and clinical studies of 3 contraceptive devices in Helsinki during 1983 and 1985. The newest and most experimental device was the intracervical device. (ICD), currently in Phase II clinical trials. The ICD is placed in the cervical canal with its horizontal arm resting in the lower part of the uterus. On its vertical arm is a Silastic rod containing 50% levonorgestrel covered by Silastic tubing. The device releases 20mcg levonorgestrel/day. The advantages of the ICD are that it is independent of the size of the uterus, and its insertion does not require trained medical personnel. The levonorgestrel improves contraceptive efficacy, reduces pain and bleeding, and minimizes risk of infection. The control devices were the Nova-T copper IUD and the levonorgestrel-releasing IUD. The Nova-T is a plastic device with its vertical arm bound with copper wire with a silver Nova-T containing 50% levonorgestrel, released at 20mcg /day. It is currently completing Phase III clinical trials. The final study sample consisted of 98 volunteers using the ICD, 86 randomly selected women using the levonorgestrel IUD, and 69 randomly selected women using the Nova-T. All of the women were previous users of some form of effective contraception; 70-80% had used nonhormonal IUDs, and 1-8% had used hormonal IUDs. The dependent variable was the discontinuation rate during the 12-month test period. At 1st analysis, it appeared that a significantly higher proportion of ICD users (22.4%) discontinued than levonorgestrel IUD users (8.7%). However, these results reflect severe selection bias,since the 98 volunteer were self-selected and predisposed to be dissatisfied with contraceptive methods in general and IUDs in particular. 9 specific variables associated with discontinuation were identified and used to construct and IUD attitude index representing negative attitudes toward prior methods. After adjustment for these group differences through logistic regression analysis, the estimated probability of discontinuing became 11.8% for the ICD, 6.2% for the levonorgestrel IUD, and 7.9% for the Nova-T. These low probabilities of discontinuation indicate that the ICD is likely to be accepted by women and that hormonal IUDs in general are more acceptable than nonhormonal IUDs. The study also showed the importance of attitude, and therefore of counseling, in contraceptive decision-making. The most important implication of the study, however, is meaningful data can be extracted from an experimental study participants were not selected randomly.

[Indexed for MEDLINE]

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