Investigators called 1,800 providers listed by more than 200 health plans under contract with Medicaid in 32 states. In all cases, insurers confirmed that the doctors were supposed to be taking Medicaid patients.

Among the providers who offered appointments, the median wait time was two weeks. (The number of providers above the median is the same as the number below it.)

“Over a quarter of providers had wait times of more than one month, and 10 percent had wait times longer than two months,” the report said.

The delays can have significant implications for patients.

“For example,” the report said, “a number of obstetricians had wait times of more than one month, and one had wait times of more than two months for an enrollee who was eight weeks pregnant. Such lengthy wait times could result in a pregnant enrollee receiving no prenatal care in the first trimester of pregnancy.”

Primary care providers, such as family doctors, internists and gynecologists, were less likely to offer appointments than specialists, the report said. But specialists tended to have longer wait times, with a median wait of 20 days, compared with 10 days for a primary care provider.

Marilyn B. Tavenner, the administrator of the Centers for Medicare and Medicaid Services, agreed with recommendations in the report to ensure access to care for Medicaid beneficiaries and to correct errors in provider directories. “Inaccurate provider directory data may unnecessarily delay an enrollee from selecting a provider,” she said.

Dr. Rachel Z. Chatters, a pediatrician in Lake Charles, La., who cares for hundreds of Medicaid patients, said it was difficult to find doctors for them when they became adults. In addition, Dr. Chatters said in an interview on Monday, “It’s nearly impossible to find specialty care for Medicaid patients of any age with diabetes, asthma, sickle cell anemia and certain other chronic illnesses.”