Between 2010 and 2013, the number of abortions in Iowa decreased from 5,399 to 4,423, according to data compiled by The Associated Press. That represents an 18.1 percent drop.According to Penny Dickey of Planned Parenthood of the Heartland, this decline is attributable to improved access to birth control (such as IUDs and hormonal implants) and other forms of family planning services.
According to Jennifer Bowen of Iowa Right to Life, this decline is attributable more pregnancy centers (which offer counseling services for women), as well as tech devices like ultrasounds. They also believe that people who protest outside of clinics are also attributing to this decrease in abortions.
My guess is that it's actually a combination of the two explanations.