Back in 2011 and 2012, major initiatives by pro-life groups concentrated on a series of "personhood" bills. These would have banned all abortions regardless of the gestational age. The bills were written with the assumption that human life -- in the form of one human ovum and one very lucky human spermatozoon -- become a human person during the process of conception. They have not been notably successful. When subjected to a public vote, they were rejected.
One backup plan for many pro-life bills is to promote "heartbeat" bills. These make abortions unavalable if a fetal heartbeat can be detected. This can happen as early as 6 weeks after conception -- a time when many women are unaware that they are pregnant.
The backup plan for many pro-life groups is to promote "fetal pain" bills. Few women would be willing to have an abortion if they knew that the fetus would feel agaonizing pain. These bills prohibit abortions typically after 20 weeks gestation and are based on the belief that a fetus becomes sentient at about 20 weeks, its higher brain functions first become activated, and it is able to feel pain. These are not nearly as effective as the "personhood" bills or "heartbeat" bills because only about 1.4% of all abortions are performed after 20 weeks.
The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.
L.T. Strauss, et al., "Abortion Surveillance --- United States, 2003, Centers for Disease Control, 2006-NOV-24, at: http://www.cdc.gov/