CNN  — 

South Carolina Gov. Nikki Haley signed a bill into law on Wednesday that makes it illegal for a woman to obtain an abortion after her pregnancy reaches 20 weeks, press secretary Chaney Adams said.

The law takes effect immediately. Abortions may be performed after 20 weeks only if the mother’s life is in jeopardy, Adams said. The bill does not provide exceptions for rape or incest.

The Pain-Capable Unborn Child Protection Act says there is “substantial medical evidence” that fetuses can feel pain by 20 weeks.

“After twenty weeks, the unborn child reacts to stimuli that would be recognized as painful if applied to an adult human, for example, by recoiling,” the bill says.

A 2005 study in the Journal of the American Medical Association found that “fetal perception of pain is unlikely before the third trimester. Although ultrasound monitoring can show intrauterine fetal movement, no studies since 2005 demonstrate fetal recognition of pain,” a statement from the American Congress of Obstetricians and Gynecologists said (PDF).

The group cited the study in a 2013 position on fetal pain, arguing that “facts are very important, especially when discussing the health of women and the American public.”

The third trimester begins 28 weeks into pregnancy.

The Republican governor’s signature makes South Carolina the 13th state to enforce a ban, along with Alabama, Arkansas, Indiana, Kansas, Louisiana, Mississippi, Nebraska, North Dakota, Oklahoma, Texas, West Virginia and Wisconsin.

Any physician who violates the law is guilty of a misdemeanor offense and faces a maximum sentence of three years imprisonment plus a potential fine.

CNN’s Keith Allen contributed to this report.