If a pregnant employee wants to work in the 6 weeks before her due date her employer can ask for a medical certificate within 7 days that states she can continue to work and it’s safe for her to do her normal job.
If a woman receives a certificate that says she is fit for work but it is not safe for you to continue in your normal job then you will be entitled to a safe job or no safe job leave. If a medical certificate says you cannot continue work at all then the employer can direct you to start unpaid parental leave. This leave will then deduct as normal from your overall entitlement.