Your iPhone may now be a form of birth control, economists warn.

New research is linking America’s plummeting birth rate to the rise of the iPhone, providing evidence that smartphone use is causing people to have fewer children. A working paper published this month in the National Bureau of Economist Research (NBER) found that in the first four years of the iPhone’s release, geographies with access to the device saw reduced births from 4.5% to 8% for ages 15 to 19, and a 3.2% to 6.6% reduction in births for ages 20 to 24. These birth rates decreased the most among teenagers, but were reduced in every age group.

From June 2007 to Feb. 2011, AT&T was the only provider distributing the iPhone, which pioneered smartphone technology, meaning the researchers were able to create a natural experiment by looking at the areas of the country in which AT&T was selling the device and then compare them to parts of the country where the phone was not yet being sold. The study looked only at the period of time when AT&T had a monopoly over iPhone sales.

Even after controlling variables relating to home prices across the country or regions that were more or less urban, researchers still found a relationship showing greater iPhone sales meant less fertility.