(FORTUNE Small Business) – Picture Cindy Crawford in a tent dress. Not a pretty picture? Lucky for Crawford, who gave birth last summer, she was able to spend the only months she has ever had a belly decked out in $200 flare pants from couture designer Liz Lange. Lange's philosophy: "Women don't want to wear clothes they would not wear when they aren't pregnant. Nine months is a long time."

Thus ends the long fashion exile for mothers-to-be. The successes of Lange's New York City shop and online store, in fact, are the second stage of the maternity mutiny that has made Prada and pregnancy bedmates. It's a revolution led almost entirely by small companies.

Modern maternity can be dated back to 17 years ago and the first pregnancy of engineer Rebecca Mathias, who came up empty when she tried to find a navy suit. She birthed a $300 million, publicly traded company called Motherswork, which today has more than 600 stores under names such as Mimi Maternity, Motherhood, and Pea in the Pod.

Mathias' feat helped inspire boutique lines L'attesa and Japanese Weekend Wear, and niche companies such as Belly Basics and Mothers in Motion.

The pregnancy market has always been hospitable to the small player, because big-label manufacturers and department store chains have virtually ignored the $600 million audience. It may have to do with the still durable view that rotundity in women means fashion death. Small companies preceded the big guys in recognizing the large-size market, according to Wendy Leibmann of WSL Strategic Retail. (That market is 25% of the women's apparel industry, at $23.7 billion.)

Now, as the market expands, even the big retailers are bellying up to the bar. Department stores such as Bloomingdale's have found a corner for new offerings from companies such as Belly Basics. Created five years ago by Cherie Serota and Jody Kozlow Gardner in New York City, Belly Basics sells the top-selling Pregnancy Survival Kit, a wardrobe in a box made of four key pieces: a dress, a skirt, a tunic, and leggings.

The next frontier: mothers who wear in-line skates to the delivery room. Marathoner Bess Hilpert recognized that pregnant women don't stop exercising, but they don't have anything "supportive" to wear. Her Mothers in Motion line has yoga suits, extra-support bras, bikinis, and even hot pants.

The latest destination is the Web, which has special appeal for pregnant women. "They are more likely than ever to have serious professional jobs and less likely to have the time to drive to the mall," says Forrester analyst Evie Black Dykema. Laurie McCartney founded Babystyle.com as a one-stop maternity shop. She just raised $14 million in a second round of financing.

But the real insight might come from companies such as Maternitycloset.com. Why sell an outfit for nine months when the customer's shape changes every week? Enter the tuxedo rental model. Go to a site, rent something for a trimester, and return it soiled with pickles and ice cream. No problem. They do the dry cleaning.