a theorem of Fontaine states that there are no curves of genus $\geq 1$ over $\mathbb Q$ with everywhere good reduction.
For curves of genus one over number fields, this is not true. There are number fields where one can construct elliptic curves with everywhere good reduction (e.g. http://arxiv.org/abs/1410.0651).
But what if we go over to genus $\geq 2$ ? Is there a statement like
There is no curve of genus $\geq 2$ over a number field with everywhere good reduction.
?
Kind regards,
reinbot