Estimations of attributable risk
Fifty-six percent of the increase in caesarean deliveries (from 19% to
30%) could be attributed to changes in the distribution of maternal
factors including maternal age, BMI, parity and history of previous
caesarean delivery (Table 4). Over the time-period, the caesarean
delivery rate would have increased from 19% to 25.3% based on
differences in maternal parity, age, and BMI alone. Sixty-six percent of
the increase in caesarean deliveries (from 19% to 30%) was accounted
for when changes in caesarean deliveries for malpresentation, multiple
gestation, and preterm birth were considered, and 78% was accounted for
when planned (pre-labour) caesarean deliveries for maternal choice,
suspected fetal compromise, a previous pregnancy issue or a suspected
large fetus were excluded from the analysis. This left 22% of the
increase in caesarean deliveries unexplained.
Expressed as a proportion of all births, the prevalence of planned
caesarean deliveries for: maternal choice increased from 0.20% to
0.64% of all births; suspected fetal compromise increased from 0.33 to
1.36%; a previous pregnancy issue (such as anal sphincter injury,
pelvic floor trauma, or difficult birth) increased from 0.0% to 0.66%;
suspected large fetus increased from 0.24% to 0.55%.