Unless you're taking the micky and 'milking it' over your recent accident (which I doubt, because you're asking us for advice on it), you cannot be disciplined for taking sick leave.
However, your employer can insist that you attend an interview with HR or Occupational Health, with a possible view to dismissal, suspension or redeployment on the grounds that you're medically unfit to do your job and will be so for the foreseeable future. Where I work (a local council), this kicks in automatically after a set period, but people are generally sensible enough to be able to tell genuine sickness from plain skiving.
You cannot be dismissed for being pregnant. In fact, you have certain rights, such as paid time off for attending ante-natal appointments etc. Maternity leave and pay rights used to depend on how long you'd worked for the company, but it's twenty-odd years since I had my kids, so that may have changed.
You may get some advice from your trade union, if you're a member of one. If not, I suggest you speak to your company's HR department, or perhaps CAB.