Estimating class numbers over metabelian extensions

Let $p$ be an odd prime and $L\mathrm{/}K$ a $p$-adic Lie extension whose Galois group is of the form ${\mathbb{Z}}_p^{d-1}⋊{\mathbb{Z}}_p$. Under certain assumptions on the ramification of $p$ and the structure of an Iwasawa module associated to $L$, we study the asymptotic behaviours of the size of the $p$-primary part of the ideal class groups over certain finite subextensions inside $L\mathrm{/}K$. This generalizes the classical result of Iwasawa and Cuoco-Monsky in the abelian case and gives a more precise formula than a recent result of Perbet in the non-commutative case when $d=2$.