U.S. law considers viability to be between 22 and 24 weeks, but states mark the point when abortion can be banned.
The research on fetal pain is conflicting. Some research indicates that nerve endings that form early in development enable the fetus to feel pain.
Dr. Kanwaljeet, "Sunny" Anand, principal investigator at University of Tennessee Health Science Center, who testified in 2004 regarding the federal partial birth abortion ban, said that at 20 weeks gestation, a fetus would experience "severe and excruciating pain."
But other research suggests pain cannot be felt before the 29th week. A study published in October 2010 in the Journal of the American Medical Association concluded that evidence of fetal pain is limited. The study noted that neither withdrawal reflexes nor hormonal stress responses to invasive procedures proved the existence of fetal pain because those reflexes could be elicited by a non-painful stimulus.
The Royal College of Obstetrics and Gynecology in London has concurred with that position.
"We see new bills every day or so and they mirror Nebraska's and Oklahoma's type of language," said Elizabeth Nash, a public policy associate at the non-profit Guttmacher Institute. "We don't know when the fetus feels pain. ... Science knows a lot, but they don't know everything."
"This is not a place for legislators," said Nash. "This is a place for a woman and her family and her physicians. And for women in these situations -- these laws do them no good. ... These laws are not about public health, they are simply efforts to ban abortion."
Danielle and Robb Deaver argue that their daughter, who gasped for breath and died in her arms 10 days following the initial complications after a natural birth, likely was in great pain in utero as she waited her inevitable death.
Their ordeal began on Nov. 28, as they were putting their 2-year-old son Alex to bed and Danielle Deaver's water broke.
Robb Deaver, an emergency room admission staffer, raced his wife to the hospital, hopeful when doctors told them the pregnancy was not necessarily over. Sometimes, women make more amniotic fluid, they said.
But the next day, an ultrasound showed little amniotic fluid around the baby and Danielle was confined to 24 hours bed rest.
Two days later, she consulted a perinatologist who diagnosed anhydramnios, a premature rupture of the membranes before a fetus has achieved viability.
The baby likely would be born with contractures -- shortening of the muscle tissue. Because its skull still was soft, the uterine muscle would cause deformities. The couple desperately hoped for a miracle, talking to doctors about bed rest, fluid replacement or use of steroids to save the pregnancy.
Specialists from the University of Nebraska Medical Center estimated that the fetus had a 10 percent chance of having a heartbeat and being able to breathe independently and, if it survived, an even smaller chance of being able to perform basic functions such as eating.
So the couple asked doctors if they could put an end to their child's pain and induce the pregnancy, as they had with a previous miscarriage.
"We weighed the options and asked millions of questions and decided together that this was the best option for all of us," said Danielle Deaver.
However, the new law had gone into effect Oct. 15.