Having trouble getting pregnant? These 10 common obstacles -- from vitamin A to personal lubricants  -- may be to blame. Plus, find out how to boost your fertility. Getting pregnant is a snap, right? You've got the partner, it's the right time of life (and month)  -- so let the baby-making begin! Not so fast. Experts say fertility problems  --  such as advancing age, a history of sexually transmitted diseases, weight issues and a low sperm count  --  can put the brakes on reproduction. So while conception is a slam-dunk for some, many others struggle to get pregnant. "A healthy 20-year-old has only a 20%-25% chance of getting pregnant each cycle," says John Norian, M.D., a fertility specialist at Loma Linda University's Center for Fertility in California. In fact, among married women ages 15-44, 2.1 million (or 7.4%) were infertile in 2002, the latest period for which the Centers for Disease Control and Prevention (CDC) has statistics. And an impressive 9% of U.S. women ages 18-44 received fertility services, such as drugs, artificial insemination, embryo freezing and in vitro fertilization, that same year. Here are the top 10 fertility missteps: 1. Waiting too long You're approaching 40 and still holding off on motherhood, wanting to climb one more rung on the career ladder. Besides, even women at age 55 bear children (with someone else's eggs, in most cases). So what difference does a few more years make? A lot. Although you may be as fit as a teenager  --  exercising