Can holding your pee while pregnant cause miscarriage? I held it in last night when I fell asleep. I'm 18 weeks

No. The only thing that can happen to you is an increased risk of a urinary tract infection. In addition, you might notice that while pregnant if you hold your pee too long.... You'll suffer from something that typically happens to women 40 years older than you are.... You'll lose urine when you cough or laugh or sneeze, i.e. Pee your pants! good luck and pee more often :-).