Get legal advice. They can not sack you for pregnancy related illness, but they can sack you after 6 weeks absence if your absence is having a significant detrimental impact on the business - it's quite hard to prove they're lying on this one. I took legal advice (was verbally told it's impossible to provide a reliable service when I keep taking a year or more off in a go to have babies) and was told because it was maternity and gender discrimination it meant court, and I needed to be able to fund the fees upfront as in this kind of case neither side can reclaim fees from the other, and at the end of the day I could only get 3x my annual salary if I was found to have been unfairly dismissed, but usually it was closer to 1x-1.2x. Solicitors fees and court fees would have come to £8-£12k in their estimation. I let it go but I was livid that employers basically have carte blanche on employment equality now.