It's unique to every woman who experiences it, but some things about pregnancy never change. It still takes 40 weeks from conception to birth, give or take a week or two; you can count on gaining an average of 30 pounds if you eat properly; and you're probably going to suffer the nausea and vomiting associated with morning sickness, especially if it's your first child. (Hint: Keep some saltines or rice cakes on your night stand.)

Yet as author Heidi Murkoff points out in the revised fourth edition of "What to Expect When You're Expecting" (Workman, $14.95), there are a couple of new trends, too, when it comes to having babies. For instance, a growing number of women are having children well into their 40s, and more moms than ever before are working right through to the delivery. What's more, the number of multiples is soaring, with twin births increasing more than 50 percent in recent years and higher-order multiple births (triplets and more) jumping a whopping 400 percent, partly due to an increase in fertility treatments.

But not to worry: Ms. Murkoff covers those topics, and many more, in her authoritative and often humorous voice. She even anticipates a few subjects you might feel silly broaching, such as how to accurately read a pregnancy test -- it can be harder than you might think -- and whether or not you can safely talk on a cell phone, use a microwave or sit in a hot tub while pregnant. (Yes, yes and no.)

Like the previous best-selling editions, this new book is heavy on the baby basics. For instance, it starts with recommendations on what to do or, perhaps more important, what not do before you get pregnant. It then guides the reader through what can be a scary first visit with a practitioner and discusses the various birthing options. There's also a comprehensive week-by-week guide on how your baby is developing that's paired with information on how the mom-to-be should be feeling.

Other topics that have helped launch this popular book almost to bible status (it was named one of the 25 most influential books of the past 25 years by USA Today) include what the care provider will do during each month's visit, how to manage pregnancy complications, and a detailed description of what you can expect during the labor and birthing process.

New material includes a chapter on carrying multiples, a chapter devoted to developing your "pregnancy profile" (a compilation of your gynecological, general medical and obstetrical histories), and a chapter on healthy eating. There's also expanded sections on complementary and alternative medicines, including acupuncture and biofeedback, and pregnancy sex. (Ms. Murkoff advises getting adventurous but keeping your expectations within reality's reach.) Readers also will get more information on beauty during pregnancy, including makeup tips and ways to safely pamper your changing body. (Highlights and waxing are OK, tanning beds and saunas are verboten.)

And because that big baby bump is being celebrated as never before on the red carpet and magazine covers, Ms. Murkoff wisely devotes several pages to maternity fashion. The book also provides tips on fitting pregnancy-friendly exercise into an expectant mom's busy (and often tiring) schedule.