DID ABRAHAM REQUIRE DIVINE INTERVENTION IN ORDER TO HAVE CHILDREN?

Genesis 17:17  Then Abraham fell upon his face, and laughed, and said in his heart, Shall a child be born unto him that is an hundred years old? and shall Sarah, that is ninety years old, bear? (KJV)

Genesis 25:1-2   Then again Abraham took a wife, and her name was Keturah.  And she bare him Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah.

Note: The assumption of contradiction is in the fact that Abraham and Sarah are unable to concieve children until God intervenes, but Abraham seems to have no problem conceiving children with Keturah (with whom he had six children). However, the difficulties in conceiving with Sarah have to do with Sarah's age, not Abraham's.