Bayer was willing to pay $31 (23.7 euros) per share for all the stock in Conceptus, and would formally launch a public offer within the next ten days, the German pharmaceuticals and drugs company announced Monday.

The deal, which was already agreed by the boards of the two firms, was estimated to be worth $1.1 billion (852 million euros), Leverkusen-based Bayer said in a statement. The acquisition was part of Bayer's efforts to expand its contraceptive and birth control business.

The takeover was a strategic "bolt-on" acquisition and an "excellent fit" in the world's most important health care market, Bayer Chief Executive Marijn Dekkers said.

Conceptus produces Essure - a permanent birth control device which is inserted into a woman's fallopian tubes. The firm is based in Mountain View, California, and employs about 300 people.

Conceptus Chief Executive Keith Grossman said in the statement released by Bayer that Essure would benefit from Bayer's global presence.

Bayer and Conceptus hope to complete the merger by the middle of 2013, stressing that the deal was still subject to approval by anti-trust authorities.

uhe/kms (AP, dpa)