Watch a live feed of the proceedings, courtesy of The Texas Tribune, below:
Before Davis began speaking, her chair was removed. Rules stipulate she remain standing, not lean on her desk or take any breaks -- even for meals or to use the bathroom.
When combined in a state 773 miles wide and 790 miles long and with 26 million people, the measures would become the most stringent set of laws to impact the largest number of people in the nation.
In her opening remarks, Davis said she was "rising on the floor today to humbly give voice to thousands of Texans" and called Republican efforts to pass the bill a "raw abuse of power."
If the filibuster succeeds, it could also take down other measures. A proposal to fund major transportation projects as well as a bill to have Texas more closely conform with a recent U.S. Supreme Court decision banning mandatory sentences of life in prison without parole for offenders younger than 18 might not get votes. Current state law only allows a life sentence without parole for 17-year-olds convicted of capital murder.
Davis was greeted by loud applause and cheers of "Go Wendy!" from hundreds of abortion-rights activists who packed the Senate. Davis motioned for them to be quiet and Republican Lt. Gov. David Dewhurst, who presides over the chamber, warned the spectators against making loud outbursts.
The sound of small children crying could occasionally be heard from the gallery.
Davis said she would use up large chunks of time reading into the record testimony from women and doctors who would be impacted by the changes.
Democrats set up the filibuster after thwarting two attempts Monday by majority Republicans to bring the abortion bill to a floor vote ahead of its scheduled time.
"We want to do whatever we can for women in this state," said Sen. Kirk Watson of Austin, leader of the Senate Democrats.
The bill would ban abortion after 20 weeks of pregnancy and force many clinics that perform the procedure to upgrade their facilities and be classified as ambulatory surgical centers. Also, doctors would be required to have admitting privileges at a hospital within 30 miles -- a tall order in rural communities.
"If this passes, abortion would be virtually banned in the state of Texas, and many women could be forced to resort to dangerous and unsafe measures," said Cecile Richards, president of Planned Parenthood Action Fund and daughter of the late former Texas governor Ann Richards.
Democrats had warned the filibuster was coming. They chose Davis to lead the effort because of her background as a woman who had her first child when she was still a teenager.
"Democrats chose not to negotiate, and we could not get the block undone," said Lt. Gov. David Dewhurst, a Republican who controls the flow of Senate legislation. He refused to declare the issue dead -- but others were less optimistic.
Sen. Dan Patrick, R-Houston, said the Democrats never should have been allowed to put Republicans "in a box" and complained that many in the Senate GOP were "flying by the seat of their pants."
But the bill's bogging down began with Republican Gov. Rick Perry, who summoned lawmakers back to work immediately after the regular legislative session ended May 27 but didn't add abortion to the special session to-do list until late in the process. The Legislature can only take up issues at the governor's direction during the extra session.
Then, House Democrats succeeded in stalling nearly all night Sunday, keeping the bill from reaching the Senate until 11 a.m. Monday.
Debate in that chamber ranged from lawmakers waving coat-hangers on the floor and claiming the new rules are so draconian that women are going to be forced to head to drug war-torn Mexico to have abortions.
At one point, the bill's sponsor, Republican Rep. Jodie Laubenberg of Spring, errantly suggested that emergency room rape kits could be used to terminate pregnancies.
Copyright 2013 The Associated Press.