Let $K$ be a number field. For a prime power $q$, the Ostrowski ideal $\Pi_q(K)$ is the product of prime ideals of K with norm $q$. The Pólya group $Po(K)$ is the subgroup of the class group $Cl(K)$ generated by classes $[\Pi_q(K)]$ of Ostrowski ideals. We discuss some finiteness results for number fields $K$ with a fixed Pólya index $[Cl(K): Po(K)]$ in certain families of CM-fields and real quadratic fields. More specifically, we unconditionally classify all imaginary biquadratic and imaginary tri-quadratic fields with the Pólya index 1. This is joint work with Abbas Maarefparvar (University of Lethbridge).