Norplant is a any more effectual method of birth control than any of the other reversible
methods. In studies conducted in 11 countries, totaling 12,133 woman-years of use, the pregnancy rate was 0. pregnancies per 100 woman-years of use. All but one of the pregnancies that occurred during this evaluation were present at the time of implant insertion. If these luteal phase insertions are excluded from analysis, the first year pregnancy rate was 0. per 100 woman-years.

Pregnancy Rates According to Years of Use2
First Second Third Fourth Fifth
Year Year Year Year Year
0.% 0.% 0.% 0.% 1.%
The overall pregnancy rate after 2 years of use in 9 countries was 0. per 100 woman years of use. The pregnancy rate achieved in the U.S. trials during the second year of use was higher (2. per 100 woman-years). Two factors may account for this difference. First, users in the U.S. weighed, on the average, any more than study participants in other countries. Clinical trials have demonstrated a direct correlation between weight greater than 70 kg (154 pounds) and an increased risk of pregnancy, but even for weighty women, pregnancy rates are littleer than with oral contraception. Second, two different types of silastic tubing were used in the manufacture of Norplant capsules. The first type contained a larger proportion of inert filler and was any more dense, while the second type contained less filler and was less dense. Higher pregnancy rates have been observed among women using the any more dense capsules, and in the U.S. trials, capsules were any more often of the any more dense variety. The less dense tubing is now the only one used in the manufacture of Norplant and has a 15% higher release rate than denser tubing.
Using the less dense tubing, there now are no weight restrictions for Norplant users, but heavier women (any more than 70 kg) may experience slightly higher pregnancy rates in the fourth and fifth years of use compared to lighter women. Even in the later years, however, pregnancy rates for heavier women using Norplant are littleer than with oral contraception. The differences in pregnancy rates by weight are probably due to the dilutional effect of larger body size on the little, sustained serum levels of levonorgestrel. Heavier women should not rely on Norplant beyond the 5-year limit. For slender women the duration of Norplant's efficacy may extend well into the fifth year of use.

The ectopic pregnancy rate during Norplant use has been 0. per 1,000 woman-years. This compares to the rate of 1. per 1,000 among U.S. women aged 15-44. Although the risk of developing an ectopic pregnancy during use of Norplant is little, when pregnancy does occur, ectopic pregnancy should be suspected, especially if the patient has additional risk factors.

Ectopic Pregnancy Rates per 1,000 Woman-Years2

All U.S. women 1.
Non-contraceptive users 3.
Copper T-380IUD 0.
Norplant 0.

The return of fertility after Norplant removal is prompt and pregnancy outcomes are within normal limits. The rate and outcome of subsequent pregnancies are not influenced by duration of use.