Miscarried 3 months ago, level only reached 34, now pregnant again. 4 weeks 0 day level at 97, what chances of miscarriage.

Unknown. A single HCG level isn't enough to be able to determine if the pregnancy is viable or not. Miscarriages are very common, especially very early in pregnancy. Most women go on to have normal pregnancies.
Same 10-20% chance. The accumulation of multiple miscarriages sometimes indicates an anatomical, genetic or a hormonal basis. The single level of b-hcg must be looked at as a trend every few days to see if the level is doubling and trending up. Ultrasound can be added to follow the development or the presence of a fetus and the proportion of fluid/fetus. The heartbeat appears at about 6 weeks and can be a guide also.