Yes, all classes are suitable for beginners, most yoga poses can be adapted to suit each individuals varying levels of strength and flexibility. You also don't need to be flexible to start!
Please check with your GP prior to attending the class that yoga would be suitable for you. Having said that yoga can be beneficial to many various illnesses and injury as it promotes body awareness and working within the limits of the body.
Although yoga can be very beneficial during pregnancy I currently do not teach pregnancy specific classes. Please take a look at the British Wheel of yoga to find suitable teachers near you.