NB = number of women with a term cephalic singleton birth in Group B
and
\begin{equation} {\text{Proportion\ of\ the\ increase\ in\ the\ caesarean\ delivery\ rate\ attributed\ to\ maternal\ factors}\backslash n}{=\ \frac{RR_{\text{unadj}}-RR_{\text{adj}}}{RR_{\text{unadj}}-1}}\nonumber \\ \end{equation}\begin{equation} \nonumber \\ \end{equation}\begin{equation} {\text{\ R}R_{\text{unadj}}=unadjusted\ relative\ risk\ for\ group\ B\ compared\ to\ Group\ A;\ \backslash n}{RR_{\text{adj}}=relative\ risk\ for\ group\ B\ compared\ to\ Group\ A\ adjusted\ for\ maternal\ factors;}\nonumber \\ \end{equation}
We additionally assessed the impact of changes in each of the other three strata ([2] preterm singleton births; [3] multiple gestations; [4] term non-cephalic singleton births) using the following formula:
\begin{equation} {Increase\ in\ number\ of\ caesarean\ deliveries\ attributable\ to\ changes\ in\ management=\backslash n}{\text{Increase\ in\ number\ of\ caesarean\ deliveries\ among\ women\ in\ each\ stratum}\backslash n}{=\ \left(P_{B}-P_{A}\right)\times N_{B}}\nonumber \\ \end{equation}
where Pi = proportion of all women within the stratum in Group i who had a caesarean delivery, and