Ito Isometry under conditional expectation

Question

Consider the process $X_t$, where: $$X_t \equiv X(t) - X(t-1) = \int_{t-1}^{t} \sigma(s) \, dW(s).$$ I want to obtain an expression for the conditional variance of $X_t$, i.e. $var(X_t|\mathcal{F}_{t-1})$. So far my attempt is: $$var(X_t|\mathcal{F}_{t-1}) = E\left[\left(\int_{t-1}^t \sigma(s)\,dW(s) \right)^2 | \mathcal{F}_{t-1} \right] = E\left[\int_{t-1}^t \sigma^2(s)\,ds | \mathcal{F}_{t-1} \right]$$ by the Ito Isometry. However, I am not sure that Ito Isometry can be exploited in the conditional expectation framwork.