“Early approaches to restricting abortion access were directed largely at patients — the demand side of the market,” Theodore Joyce, a professor at Baruch College, writes in a new article. Thirty-six states, for example, require parental involvement in a minor’s abortion, according to the Guttmacher Institute. Twenty-five mandate a waiting period, usually 24 hours.

Increasingly though, laws have targeted the supply-side of abortion: the doctors. Both Kansas and Virginia this passed stringent new licensing standards for abortion clinics. The Kansas regulation requires procedure rooms of at least 150 square feet and janitorial space of 50 square feet. Dressing rooms for patients must have a toilet, washing station and storage for clothing. Virginia has required abortion clinics to comply to hospital standards, which often means widening hallways and expanding procedure rooms. Other states, like Missouri, have also passed similar, supply-side restrictions in recent years.

Supply side restrictions on abortion seem to have a big impact. Joyce’s paper looks at a recent Texas law, which had both a demand side component (a 24-hour waiting period) and a supply-side one (all abortions after 16 weeks had to be performed at a surgical center). He finds that abortions after 16 weeks saw a much more dramatic drop, indicating that the latter restriction had a more powerful effect than an across-the-board waiting period.