advice on announcement

Dani
So I'm 4 weeks 2 days pregnant and my doctors appointment is tomorrow. I'm very excited and still feel in awe it's finally happened.
I planned to tell my parents next week and not tell friends or family until first scan.
Yesterday my mum sat me down and said my sister had a miscarriage  in December and had tests results back. Apparently she lost the baby after a couple of weeks and is devastated. 
I'm so sad for my sister and now very wary about saying anything to anyone but my husband about being pregnant. I've cried hard for my sister and have no idea how to be gentle about my announcement.
I want to share how happy I am, but don't think it's appropriate. 
Advice please?