Dear Prashant,
A small but important correction to the first part of your answer. Confirmation of a probationer can not be automatic unless there is a specific provision for "deemed confirmation" in the contract of employment or the standing orders. As long as there is no orders in writing by the employer, the employee remains a probationer only.
Once the Maternity Act,1961 becomes applicable to the establishment, the employment status of the women employee whether she is a confirmed one or probationer or temporary does not matter. As rightly observed by other members above, what is required is that she ought to have worked for 80 days in the preceding 12 months period.