Final answer:
The influence primarily comes from health maintenance organizations (HMOs) and private insurers who provide a fixed amount per person enrolled in the plan and set limits on coverage for maternity care.
Step-by-step explanation:
The postpartum hospital stays that are becoming shorter are primarily the result of the influence of health maintenance organizations (HMOs) and private insurers. HMOs provide healthcare that receives a fixed amount per person enrolled in the plan, regardless of how many services are provided. As a result, healthcare providers have an incentive to reduce the quantity of care provided. Private insurers also play a role in shortening postpartum hospital stays by setting limits on the length of coverage for maternity care.