Results
Health outcomes, resource use and costs are summarised in Table 1
by method of IOL. Most women in the balloon and PG group were
nulliparous (72.7% and 67.1%, respectively) and birthed vaginally
(67.8% and 73.6% respectively), with more women in the PG group
starting IOL with a more favourable cervix (MBS>3) compared
to the balloon group (56.2% vs 47.7%). Health utility index scores
showed lower health scores for nulliparous (0.726 balloon vs 0.694 PG
group) than for parous women (0.80 balloon vs 0.834 PG groups) and
higher health scores for vaginal birth (0.804 unassisted, 0.705
instrumental) compared to CS (0.643). Health utility scores were
marginally higher for women starting IOL with a less favourable (MBS≤3
compared to more favourable cervix (0.744 vs 0.738). Balloon catheters
cost $49 and the mean cost of PG cervical ripening was $105. Hourly
cost of care in the antenatal ward was $51, $259 in the birth suite,
$48 in the postnatal ward and $81-$125 in the neonatal nurseries.
Deterministic model analyses showed costs in the balloon group
(n=205) and PG group (n=243), were $9,765 versus $10,272 per QALY
gained, retrospectively (see Table 2). The balloon group absolutely
dominated the PG group with lower mean costs ($7,294 vs $7,585) and
higher mean effectiveness (0.75 vs 0.74 QALYs), resulting in a negative
ICER which indicates cost savings of $34,193 per quality-adjusted life
year gained if this method of induction was chosen. The net monetary
benefit (NMNB) of outpatient-balloon IOL was $30,054 compared to
$29,338 in the PG group.
In probabilistic sensitivity analyses (PSA) using Monte Carlo
simulation, the balloon group had a higher probability of being
cost-effective at each WTP threshold tested (see Figure 1). At a WTP of
$50,000 the likelihood of outpatient-balloon IOL being cost-effective
is 55.25% compared to inpatient-PG IOL (44.75%). Figure 2 shows the
scatter plot on the incremental cost-effectiveness plane for both
methods. The eclipse represents the 95% confidence interval of all
simulated pairs of incremental cost-effectiveness from the 10,000
simulations. A total of 34.2% of all simulations fell in the south-east
quadrant representing possible results in which outpatient-balloon IOL
was less costly and more effective than inpatient-PG IOL. A further
17.8% of simulations fell in the north-east quadrant below the $50,000
WTP threshold, indicating higher costs and higher benefits of
outpatient-balloon IOL that we would be willing-to-pay for each
additional QALY (below $50,000). Another 3.3% of simulations in the
south-west quadrant indicate lower costs and lower benefits of
outpatient-balloon IOL below the WTP threshold. Overall, the area to the
right of the WTP threshold line is the number of simulations (34.2% +
17.8% + 3.3% = 55.3%) in which outpatient-balloon IOL represents the
better value for money, and the area to the left represents simulations
in which inpatient-PG IOL is cost-effective (44.7%).
Extracts of results from 1-way sensitivity analyses are
illustrated in the Supplementary material, Table S1. When the mean
operating costs per CS with baseline value of $3,447 were varied from
$1,000-$15,000, outpatient-balloon IOL had a higher NMB for each
tested value and dominated inpatient-PG IOL up to a cost of $8,442.
Furthermore, varying the mean hourly cost in antenatal ward of $51 from
$0-$150 also showed consistently higher NMB for balloon induction
which had lower costs and higher effectiveness (absolute dominance) for
values between $28 to $150. One-way sensitivity analysis of mean
hourly costs in birth suite with baseline value of $259 was tested for
values between $100-$500 and resulted in higher NMB for each value
with lower costs and higher effectiveness in the balloon group for
values up to $450. The tested ranges of mean costs of stay in postnatal
ward (baseline value $48, range $0 - $100), ICN (baseline value
$125, range $50 - $200) and SCN (baseline value $81, range $0 -
$300) resulted in absolute dominance (lower cost, higher effectiveness)
of outpatient-balloon IOL with higher NMB ($27,399 - $32,505) compared
to inpatient-PG IOL (NMB from $26,757 - $31,721).
Subgroup analyses by parity also indicated a higher likelihood of
outpatient-balloon IOL being cost-effective for nulliparous women
(64.5%) and inpatient-PG IOL being cost-effective for parous women
(66.9%). The NMB for inpatient-PG IOL in parous women was the highest
out of all types of analyses (see Table 2) with $36,969 compared to
balloon induction in parous women with $34,210 and very low mean costs
for parous women in both groups with $4,903 for PG and $5,659 in the
balloon group. Subgroup analyses by cervix favourability showed higher
mean costs for both methods of IOL for women with a more favourable
cervix (MBS >3) compared to a less favourable cervix (MBS
≤3), and higher probability (59.1%) of outpatient-balloon IOL being
cost-effective for women with a more favourable cervix (NMB $30,599 vs
$27,904). Women with a less favourable cervix had lower mean costs by
$759 and higher utility scores by 0.026 in the inpatient-PG IOL with
56.3% of simulations indicating cost-effectiveness.