Maternity Insurance is an insurance that covers hospitalization expenses during pregnancy whether it is caesarean or normal delivery. It's a mandatory in 2014 under the affordable Care Act. Maternity covers include outpatient services such as prenatal and postnatal doctor visits, gestational diabetes screenings, lab studies, medications, etc. It also covers Inpatient service, new born baby care etc.
If you are a working professional, you should check whether your employer offers maternity in the group policy or not. In a majority of corporate group policies, maternity is an add-on benefit with a specific sub-limit.