If you are going to cut your hours don't forget this will affect your mat pay
Your employer cannot sack you for being off sick whilst pregnant, what they can do however, is if you are off sick after 29 weeks with a pregnancy related illness such as morning sickness, SPD etc they can enforce maternity leave to start
Have you had your risk assessment yet?
http://www.tuc.org.uk/h_and_s/tuc-9712-f0.cfm
Your employer should actually be providing you with a rest room where you can rest as often as need be
Best of luck for this afternoon
ojx