Obama opposed the language of this type bill(s) multiple times and his explanation was that the language in the bill(s) would have been a de facto overturning of Roe V Wade through the "Equal Protection" clause of the 14th Amendment. He has said that he supported the similar federal bill that Bush signed into law since the wording protected the right to abortion. When the IL bill added an amendment that precisely mimicked the federal wording in 2005 the bill passed the IL Senate by a 52-0 vote. Obama says he supported that bill as well.
He and others rightly point out that there were already laws on the IL books protecting viable fetuses and that all life is protected by Doctor's Hippocratic Oath requirements.