I was going to say this too- depends on your work. I know for me it was from about week 30 that any sick leave counted as maternity leave. Before then not. Could you maybe go off with stress rather than pregnancy induced illness? Might give you some extra security re maternity pay.
If you’re off sick during your qualifying weeks then it might affect your maternity pay if you don’t earn enough. If you’re off sick in the last 4 weeks of pregnancy with a pregnancy related illness your work *can* enforce your maternity leave to start, doesn’t mean they will though.
It can only affect if it’s 4 weeks until your due date I believe. I would check your policy at work around maternity and sickness as it should cover it there too