Several physicians' groups sued Thursday to try to block a new law that would let lay midwives deliver babies in Missouri, a practice currently punishable by prison time.

The lawsuit claims the midwifery language violates the Missouri Constitution by going beyond the title and original purpose of the health insurance legislation to which it was secretly attached in the final weeks of the legislative session.

It also argues that allowing unlicensed midwives to practice medicine could jeopardize patients and put doctors who cooperate with them at risk of professional discipline.

The lawsuit filed in Cole County Circuit Court seeks an injunction against enforcing the new midwifery law, which is scheduled to take effect Aug. 28, while allowing the rest of the health insurance legislation to stand.

The plaintiffs include the Missouri state Medical Association, The Missouri Association of Osteopathic Physicians and Surgeons, Missouri Academy of Family Physicians and St. Louis Metropolitan Medical Society.

Sen. John Loudon, who inserted the midwifery language into the health insurance bill, complained that doctors' groups have been unwilling to compromise with him and other midwifery supporters.

"They should be coming to the table and not rushing to court," Loudon, R-Chesterfield, said Thursday. "We're the only state in the country that makes it a felony, and I don't know why they're defending that."

Midwives typically provide prenatal care and help deliver babies in mothers' homes. But under existing Missouri law, midwifery is considered the illegal practice of medicine when done by anyone other than a physician or certain specially trained nurses. It's punishable by up to seven years in prison.

Missouri is one of 10 states and the District of Columbia that prohibit "direct-entry midwives" -- those who enter the profession directly without medical or nursing degrees -- according to the Lilburn, Ga.-based North American Registry of Midwives.

The recently passed legislation says that regardless of the current felony statute, anyone with a "tocological certification" -- meaning one in obstetrics -- from a privately accredited group can provide services related to pregnancy.

Loudon acknowledged what the obscure language meant only after lawmakers had given the bill final approval. The Senate's leader stripped Loudon of a committee chairmanship for his trickery, but Gov. Matt Blunt later signed the bill into law.

The lawsuit cites two constitutional provisions. One states that "no bill shall be so amended in its passage through either house as to change its original purpose." The other section states: "No bill shall contain more than one subject, which shall be clearly expressed in its title."

The title of the bill that passed described it as "relating to health insurance."

The bill's original title, when introduced in the House, was more specific, saying it related "to portability and accessibility of health insurance."

"The midwife provision does not relate to health insurance," the lawsuit says.

The underlying bill authorizes tax credits for those who buy their own health insurance and lets people keep their individual health insurance policies when they take a job with a small business that provides a group health plan.

Another prong of the legislation expands the eligibility and lowers the premiums for people to be covered by the Missouri Health Insurance Pool, which is tailored for those who cannot afford insurance, often because they have chronic health problems.