I was on sick pay (employment and support allowance) off jobcentre for majority of my pregnancy due to stress and anxiety. Dont think you'd get it when you recieve maternity pay and not sure if it affects it. I get maternity allowance benefit because I made a couple pound less than the amount needed to quality.
Your doc would have to recommend it in writing and you could use pto or fmla if you been with your emoloyer at least one year. I believe it takes time away from your 12 weeks, but that part I'm.not certain.