An announcement may come as soon as Monday, said one of the people, who declined to be identified because the deal isn’t yet public.

Quidsi, which expects to ship 500 million diapers this year, will help Amazon cater to new parents and gain expertise in warehouse management and low-cost shipping. Amazon Chief Executive Officer Jeff Bezos, 46, bought Zappos.com Inc. last year for $1.2 billion to expand sales of shoes and clothing.

The purchase also removes a competitor for Seattle-based Amazon, which began selling diapers in mid-2006, a year after Diapers.com debuted. The company began offering a free three- month trial of Amazon Prime to mothers ordering diapers and other baby items to counter Diapers.com’s free shipping.

Drew Herdener, a spokesman for Amazon, and Lindsey Scott, a spokeswoman for Quidsi, couldn’t be reached for comment.

Amazon rose $1.84, or about 1 percent, to $170.77 in Nasdaq Stock Market trading on Nov. 5. It has risen 27 percent this year.

Founded by Marc Lore and Vinit Bharara, Quidsi generated about $180 million in revenue last year and is expected to post revenue of about $300 million in 2010, Bloomberg Businessweek reported last month. Venture backers of Jersey City, New Jersey- based Quidsi include Accel Partners, Bessemer Venture Partners, BEV Capital, MentorTech Ventures and New Enterprise Associates.

The company makes no profit from selling diapers, but instead rather by retaining customers who buy higher-margin products such as brand-name baby shampoo, wipes and formula.

Fortune reported the purchase Saturday.