Everyone should get a risk assessment- even for "desk" jobs. Sitting for prolonged periods, your commute to work, staring at a screen all comes into it! Think it's quite early it should be done so you might want to prod your employer!
Yep you should have one. Lots of risks just being at a desk, including high risk of RSI. Should also have a personal evacuation plan and buddy in case of fire. Your HR or health & safety rep should be dealing with it so do chase them up
I think a lot of employers are crap at getting on and doing them, so you may need to prod. My last employer was a bit clueless as they'd never (in their 170year history) employed a pregnant woman before! It was particularly relevant as part of my job involved potentially dangerous situations. We worked through it together though and actually once prodded were great. A lot of it can be common sense but reviewing it means that everyone is aware and can take necessary steps to avoid problems.
Meant to say it's normal to need to review as pregnancy / work arrangements change so more than one risk assessment is common. It doesn't have to be a big thing and should be tailored to the situation.
Definitely push for a risk assessment. My manager at work couldn't have cared any less about doing one, and I pestered her continuously to do one. When it had been done, my job had to be adapted for a safer working environment, especially with me being high risk. I had to change my job role, and I decided to drop the part time too.
I didn't work in an office, so not 100% sure about what your risk assessment would look like. I'm sure it would include sitting down for too long though. In the mean time whilst you're waiting for your risk assessment to be done, make sure you stand up often and do some light leg exercises to prevent blood clots.