KANSAS CITY, Mo. — The case of a Kansas sperm donor being sued by the state for child support underscores a confusing patchwork of aging laws that govern assisted reproduction in the United States and often lead to litigation and frustration among would-be parents.

Complex questions about parental responsibility resurfaced late last year, as Kansas officials went after a Topeka man who answered a Craigslist ad from a lesbian couple seeking a sperm donor. Because no doctor was involved in the artificial insemination, the state sought to hold William Marotta financially responsible for the child when the women split up and one of them sought public assistance. A hearing is set for April.

Many states haven’t updated their laws to address the evolution of family structures — such as same-sex families, single women conceiving with donated sperm or artificial inseminations performed without a doctor’s involvement. At-home insemination kits are inexpensive, and obtaining sperm from a friend, or even a donor met over the Internet, allows women to avoid medical costs that generally aren’t covered by insurance.

But experts say that as case law changes, families put themselves at risk by failing to seek legal advice.

The first wave of assisted reproduction laws were based on model legislation from 1973. These statutes typically call for, among other things, the involvement of a medical provider in order for a sperm donor to be freed of parental responsibility.

“They put a whole bunch of what they thought were reasonable restrictions on the process to encourage people to do it responsibly,” said Steve Snyder, a Minnesota family law attorney and chairman of an assisted reproduction committee for the American Bar Association. But, he said, the problem is that if people “don’t fall under the strict terms of the law, then the law doesn’t protect you.”

As a result, the doctor involvement requirement and other stipulations were dropped in 2000 when the model legislation, the Uniform Parentage Act, was updated. The new language has been enacted in nine states, including Alabama, Oklahoma and Texas. But Kansas’ law, enacted in 1994, was based on the earlier model.

Kansas isn’t alone in grappling with assisted reproduction issues. In Indiana, an appeals court ruled last week that a man who divorced his wife must pay child support for their son and daughter, even though the children were conceived by artificial insemination using sperm donated by another man. Still another case in Indiana involved a man who was ordered in 2010 to pay child support for only one of the two children resulting from his sperm donations.

“The only way to avoid these situations is to change the law to catch up with the technology and what people are actually doing in assisted reproduction,” Snyder said.

Sperm donation and parental rights may sound like a relatively niche sector in the legal arena, but updating laws has been a challenge, and some like the rules just the way they are.

Kansas’ state Senate Majority Leader Terry Bruce, a conservative Republican, said he doubts legislators will or should consider making changes.

“It tells everybody don’t do stupid things on Craigslist. It’s kind of common sense,” he said.” If you’re going to create another life, even if it’s a good intention, that’s a heck of a responsibility, and it’s one that precedes any sort of state action.”

In the 2010 Indiana case, a woman who used a friend’s sperm to conceive two children sought public assistance after she and her lesbian partner separated. County officials wanted to collect child support from the donor.

A state appeals court ultimately ruled that an agreement entered into before the first child’s birth freed the donor from financial responsibility for that child. But the donor was found to be financially responsible for the second child, because the agreement didn’t cover subsequent children.

“It is definitely evolving and these kinds of cases are really cutting edge,” said Sean Lemieux, an Indianapolis attorney who also represented the sperm donor. “It is a risky thing and this is not the place to save your money upfront and get an office form off the Internet.”

A high-profile California case, meanwhile, shows the consequences of going without a contract. Texas bodybuilder Ronnie Coleman, who donated sperm for his ex-girlfriend’s artificial insemination, paid thousands of dollars in child support each month for nearly four years for two children until an appeals court ruled in March that he could stop.

Peter A. Lauzon, the Los Angeles attorney who represented the eight-time Mr. Olympia, said the legal issues surrounding artificial insemination create a “chilling effect.”

“Who is going to want to donate sperm?” he asked. “No one.”

Mikki Morrissette, a mother of two who didn’t use a doctor for her artificial inseminations, once found herself asked to identify her sperm donor while seeking state-subsidized health insurance in Minnesota after moving there from New York City. She refused and was denied.

“I know a lot of other woman around the country who have used a known donor who have run into similar problems,” said Morrissette, who was written five books, including “Choosing Single Motherhood: The Thinking Woman’s Guide.”

She said the same request isn’t made of adoptive parents or when an anonymous donor is used: “It’s not fair.”