How does an employer determine an employee's right to statutory maternity pay?

If a woman is an employee, and is pregnant or has given birth, she is entitled to statutory maternity pay provided that her average weekly earnings are at least the lower earnings limit for national insurance purposes. She must also have been continuously employed for a minimum of 26 weeks into the qualifying week (which is the 15th week before the expected week of childbirth). Statutory maternity pay is payable for up to 39 weeks.