The provision is similar to “heartbeat” laws put on the books in Mississippi, Kentucky, Ohio and Georgia that ban abortion once a fetal heartbeat is detected. That can occur in about the sixth week of pregnancy.

Kentucky’s six-week ban was challenged after it was signed in March, and a federal judge temporarily blocked it. Similar versions of the law have been struck down in North Dakota and Iowa.

If the heartbeat provision is struck down, the bill calls for abortions at the “pain capable gestational age,” or about 20 weeks after fertilization, to be prohibited.

The Missouri proposal also includes a requirement that both parents be notified if a minor seeks an abortion. And, Republicans tacked on a provision barring abortions from being performed solely because the fetus has Down syndrome.