A nanny is typically an employee of the family, and as such is entitled to all statutory rights, leave and payment through pregnancy and maternity, paternity or adoption leave.
As soon as your nanny informs you of her pregnancy you are obliged to carry out a risk assessment, and modify her duties if there are any which are incompatible with pregnancy. This may include things such as lifting or coming into contact with childhood illnesses. If it is too risky for your nanny's or her baby's health to continue working, whether on a short or long term basis, you will need to suspend her on full pay.
Nannies are entitled to time off, paid in full, to attend maternity related appointments such as scans and midwife appointments. You will need to make alternative provision for childcare and cannot ask her to make up the hours, but you can request that she attempts to minimise disruption when planning appointments.
Your nanny should give you a MATB1 form, detailing the expected date of confinement. She will inform you of the date she intends to leave for her maternity leave. You must assume that she will take the full 52 weeks of leave. She does not have to take the full 52 weeks but must take a minimum of 2 weeks and give you appropriate notice of her intention to return to work. Any holiday owed should be taken before the baby arrives. Maternity leave is triggered automatically by the birth of her baby (at any point after 24 weeks including stillbirth, or born alive at any point) or any sickness in the 4 weeks preceding the expected due date. She can choose to start her maternity leave at any point in the 11 weeks before the expected due date.
Statutory Maternity Pay is currently recoverable from the Government at 104.5%. Your payroll provider will advise you how to proceed. You will be liable for the holiday pay accrued while on maternity leave.
Nannies who are pregnant when they start a job
A nanny who starts a new job while pregnant is still entitled to maternity leave but will not be entitled to Statutory Maternity Pay. Instead she should claim Maternity Allowance. She is still entitled to all the other protection given to pregnant employees.
Nannies and redundancy while on maternity leave
A nanny can be made redundant while on maternity leave if the job genuinely no longer exists. Any rights to redundancy payments still apply. As with any redundancy situation a nanny should be offered any suitable alternative employment, e.g. as an after school nanny, before the vacancy is advertised elsewhere.
Nannies bringing their own child to work
Nannies have the right to return to their job under the same conditions. This does not include bringining their new baby with them. You may wish to modify the conditions of employment to allow a nanny to bring her baby. At this point you are entitled to also modify the working hours and/or pay.
There is detailed information on the Gov.uk site which covers rights for pregnant employees and Maternity Leave and Payment, all of which applies to nannies.