Women who have never given birth and have used an IUD for an extended period of time face decreased fertility when they try to conceive, according to a prospective study conducted in England and Scotland.1 Thirty-nine percent of nulliparous women who discontinued IUD use to become pregnant gave birth within 12 months, compared with 54% of those who stopped using a barrier method; the proportion was significantly lower among women who had used an IUD for 78 months or more (28%) than for those who had used one for a shorter period (45%). The association between extended IUD use and decreased fertility remained after other factors that affect fertility were taken into account.
To investigate the relationship between IUD use and subsequent fertility among nulliparous women, the researchers analyzed data from 558 women who had stopped using an oral contraceptive, IUD or barrier method in order to conceive. These women had been recruited between 1982 and 1985 as part of a larger prospective study at 17 family planning clinics, and were followed up on an annual basis through 1994. Study participation was restricted to white British citizens who had never given birth, were either married or in a stable living situation with a male partner, and were using an oral contraceptive or IUD at the time of enrollment. The researchers assessed return to fertility by calculating the length of time between a woman's first discontinuation of contraceptive use in order to conceive and a term birth; they excluded from their analyses women who were lost to follow-up, did not have a term birth or resumed contraceptive use.
At the time that the women discontinued contraceptive use in order to conceive, 29% had been using an IUD, 28% oral contraceptives and 43% a barrier method. (A small number of women using the rhythm method were included in the barrier category.) Some women had recently switched methods, however: Three months prior to stopping contraceptive use, 43% had been using oral contraceptives, 33% an IUD and 24% a barrier method.
Women who had been using an IUD at the time they discontinued practicing contraception were slightly older (mean age, 27.7 years) than women using oral contraceptives or barrier methods (26.0 years for each). In addition, they were more likely to be current or former smokers (54%) than were users of other methods (41-48%), and were more likely to have a history of miscarriage, abortion or ectopic pregnancy (25% vs. 13-17%). Women using barrier contraceptives were the most likely to have a history of two or more gynecologic or other selected illnesses (9%, compared with 3-4% of pill or IUD users). Social class, as measured by the husband's occupation, was lower for women using oral contraceptives (47% had husbands working in manual occupations) than for women using other methods (33-34%); however, social class based on the woman's occupation was similar across groups.
Overall, women who had been using a barrier method achieved conception most quickly. Twelve months after stopping use, 54% of these women had given birth, compared with 39% of IUD users and 32% of those who had been taking oral contraceptives. However, 18 months after discontinuation of use, fertility was more similar among the three groups: Seventy-six percent of barrier method users, 70% of pill users and 67% of IUD users had given birth.
Duration of oral contraceptive use had no impact on fertility. However, women who had switched from oral contraceptives to a barrier method within three months before attempting to conceive were more likely to become pregnant within 12 months (54%) than were those who attempted to conceive immediately after discontinuing oral contraceptives (32%). Among women who had had an IUD, those who had used it for 78 months or longer were significantly less likely to give birth within 12 months (28%) than were those who had used it for a shorter period (46%). Too few women had switched from an IUD to a barrier method shortly before conceiving to permit analysis of the effect of such a change.
When women were classified on the basis of the contraceptive method they had used three months before attempting to conceive, fertility did not differ significantly across groups. Again, duration of use was not related to the rapidity with which pregnancy occurred among women who had taken oral contraceptives, but longer use of an IUD was associated with delayed conception. When women were classified according to whether they had ever or never used an IUD, duration of use was linked to fertility decline in a similar fashion. (Only 28 women had never used oral contraceptives; therefore, meaningful comparisons could not be made between ever- and never-users.)
In initial log-rank and proportional hazards analyses of individual factors, a number of factors were associated with delayed fertility at a significance level (p-value) of .10 or less: contraceptive method used; duration of IUD use; maternal age; social class, based on the husband's occupation; smoking history; and history of gynecologic and other illnesses. The researchers conducted a multivariate proportional hazards analysis to assess the independent effects of each of these factors on fertility.
According to the multivariate results, women who had taken oral contraceptives and those who had used an IUD for 42-78 months were less likely to give birth during follow-up than were those who had used a barrier method (relative hazard of 0.7 for each group). There was an even more dramatic decline in fertility among women who had used an IUD for 78 months or more: These women were only half as likely as barrier method users to bear a child (0.5). Older maternal age, lower social class, and a history of multiple gynecologic and other diseases were also associated with decreased fertility (0.2-0.5).
Because the types of commonly used IUDs have changed and infection screening has improved since the time that these women were recruited into the study, the researchers warn that their results "should be extrapolated to present day practice with extreme caution." Nevertheless, they conclude that "long-term use of an intrauterine device by a nulliparous woman increases the risk of impairment of fertility to a clinically important extent," and cite the well-established link between IUD use and pelvic inflammatory disease, a known cause of infertility. They conclude that "intrauterine devices should be used sparingly in nulliparous women and, in particular, that use for many years should be avoided."--A. Hirozawa
REFERENCE
1. Doll H, Vessey M and Painter R, Return of fertility in nulliparous women after discontinuation of the IUD: comparison with women discontinuing other methods of contraception, British Journal of Obstetrics and Gynaecology, 2001, 108(3):304-314.