President Obama spoke to nearly a thousand Planned Parenthood supporters Friday, telling them efforts to restrict abortion access across the country represented an effort to "turn back the clock" on women's progress.

"When you read about some of these laws, you want to check the calendar, you want to make sure you’re still living in 2013," Obama told the crowd.

In the past two months, four states — Alabama, Arkansas, Kansas and North Dakota — have adopted some of the most stringent restrictions on abortion in the nation, while Virginia has also imposed new rules on abortion providers by making them comply with hospital-style building standards. Lawmakers in 42 states have introduced legislation this year that would impose some kind of limits on access to abortions.

Obama -- the first sitting president to address the group in its nearly 100-year history -- took aim at North Dakota's law, which bans abortions as soon as a fetal heartbeat can be detected, at around six weeks.

"A woman may not even know that she’s pregnant at six weeks," he said. As long as Planned Parenthood and other groups have to fight to defend women's reproductive rights, he added later, "you’ve also got a president who will be right there with you, fighting every step of the way."

In his speech, the president highlighted the fact that women visit Planned Parenthood clinics for routine health exams as well as reproductive services. The group is guided by the idea "that women should be able to make their own decisions about their own health," he said. "It’s a simple principle."

Obama's remarks came as abortion providers face new challenges. For example, opponents are highlighting problems in abortion clinics in the mid-Atlantic region. Philadelphia abortion doctor Kermit Gosnell is currently facing trial on charges of killing one adult patient and multiple infants in his clinic.

In her introduction, Planned Parenthood President Cecile Richards praised Obama for his work to defend women's rights, including by preserving her group's federal funding during budget negotiations with Republicans and providing full coverage for birth control as part of the administration's health-care law.

"That is equity, that is justice, that’s what it means to have a president who cares about women," Richards said.

Obama was originally slated to address the group at its Thursday night gala, but he delayed his appearance a day so he could spend more time in West, Tex., at a memorial service for the 12 firefighters who died battling last week's fire and explosion at the town's fertilizer facility.

"I’m sorry I couldn’t be at the party yesterday," Obama said. "I understand it was a little wild. That’s what I heard."