Irregular shaped sac

Hi there

I had an early scan this morning and the good news was that the baby could be seen and the heartbeat was visible. I'm around 6 weeks pregnant. I was told, however, that the sac looks 'slightly' irregular and that caution should be taken over what might happen. I've had two miscarriages since Christmas and am now worried that I need to prepare myself for another. Has anyone else been told something similar and what does it actually mean?

Thanks
KT