BlogHer, a site that aims to popularize blogs by women, has raised its first round of capital from Silicon Valley firm, Venrock.

We’ve heard that the amount is $3.5 million, but this number has not been confirmed. The company has declined comment, but Venrock is acknowledging that an investment did take place.

BlogHer functions as an index of women’s blogs, a series of forums, and a destination for editorial content from more than 60 contributors on a wide range of topics. These include astrology, fashion and shopping, feminism and gender, and mommy and family.

The investment comes as content sites for women are seeing extremely rapid growth. Glam Media, another network for womens content, is one of the fastest growing sites on the Web right now. Presumably, BlogHer’s model is the same: Match advertisers with content that they can easily target, for branding purposes.

BlogHer lists blogs of all stripes, from race, ethnicity and culture, sex and relationships, to food and entertainment. The index is over 9,000 deep, and woman-friendly male bloggers are welcome to participate, even if none of them get to be editors.

Bloggers can register and add their blogs, which then get vetted by a managing editor to filter out spam.

BlogHer’s reach expands beyond the blogosphere. Since 2005, it’s hosted an annual conference, and in July of this year will hold another in Chicago. The event is sponsored by the likes of GM, Google, Yahoo and Dove.

We’re tracking and will update as necessary. We’ll add, though, that this deal has the markings of Venrock’s David Siminoff all over it. The early investor in Yahoo recently joined Venrock to invest in media related companies. We interviewed Siminoff a couple of weeks ago and he expressed interest in blog networks with potential to draw significant traffic.

Update: David Siminoff lead the investment