A First Pregnancy May Be Difficult to Achieve After Long-Term Use of an IUD

From the Guttmacher Institute on IUDs (intrauterine devices--they're put in the uterine lining to "irritate" it to prevent implantation of an embryo):

A First Pregnancy May Be Difficult to Achieve After Long-Term Use of an IUD

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.

Read more here. One might want to consider the long-term effects of birth control before choosing. Hormones, uterine irritation...even spermicides like Nonoxyl-9 may have weird biological effects.