Let $\pi \colon \mathcal {X}\to B$ be a family whose general fibre $X_b$
 be a family whose general fibre $X_b$ is a $(d_1,\,\ldots,\,d_a)$
 is a $(d_1,\,\ldots,\,d_a)$ -polarization on a general abelian variety, where $1\leq d_i\leq 2$
-polarization on a general abelian variety, where $1\leq d_i\leq 2$ , $i=1,\,\ldots,\,a$
, $i=1,\,\ldots,\,a$ and $a\geq 4$
 and $a\geq 4$ . We show that the fibres are in the same birational class if all the $(m,\,0)$
. We show that the fibres are in the same birational class if all the $(m,\,0)$ -forms on $X_b$
-forms on $X_b$ are liftable to $(m,\,0)$
 are liftable to $(m,\,0)$ -forms on $\mathcal {X}$
-forms on $\mathcal {X}$ , where $m=1$
, where $m=1$ and $m=a-1$
 and $m=a-1$ . Actually, we show a general criteria to establish whether the fibres of certain families belong to the same birational class.
. Actually, we show a general criteria to establish whether the fibres of certain families belong to the same birational class.