To qualify for maternity leave and statutory maternity pay a woman must be an employee, ie. she must work under a contract of employment. In the same way that individuals who are self-employed are not bound by statutory legislation on, for example, sick leave or holidays, any period of leave to cover the birth of a baby will be a matter of personal decision.
As a self-employed person you may, however, be able to claim maternity allowance (as opposed to the statutory maternity pay due to employees) to fund the period that you will not be working, assuming you satisfy the criteria outlined in the claim form.
You should contact your local TaxAssist accountant or local jobcentre plus office for further details, or alternatively visit the website www.direct.gov.uk