Correction to Hospital surgical volume–outcome relationship in caesarean hysterectomy for placenta accreta spectrum

Matsuo, K, Youssefzadeh, AC, Mandelbaum, RS, Sangara, RN, Matsuzaki, S, Matsushima, K, Klar, M, Ouzounian, JG, Wright, JD. Hospital surgical volume–outcome relationship in caesarean hysterectomy for placenta accreta spectrum. BJOG 2022; 129: 986–993. https://doi.org/10.1111/1471-0528.16993

The authors would like to correct the analytic approach in their investigation that assessed the association between hospital volume for caesarean hysterectomy and surgical morbidity in pregnant patients with placenta accreta spectrum. In the previous analysis, they calculated the relative hospital surgical volume as the summation of number of patients who had caesarean hysterectomy for placenta accreta spectrum over the 3-year study period by using the anonymized hospital classifiers. They would like to clarify that this analytic schema is to be corrected as the annualized number. In this annualized fashion, the relative hospital volume for caesarean hysterectomy was calculated in each year. The remaining patient-level analysis was unchanged.

The authors identified the following errors:

1. Prior Figure 1 was incorrect and the distribution of patients according to the revised relative caesarean hysterectomy hospital volume is shown in corrected Figure 1 below. Nearly two-thirds of patients in the study underwent caesarean hysterectomy where the relative hospital surgical volume was five cases a year. Nearly 10% of patients in the study population had caesarean hysterectomy at centers where the relative surgical volume was 15 or more cases a year.

FIGURE 1

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Distribution of relative cesarean hysterectomy hospital volume. Distribution of annualized relative hospital cesarean hysterectomy volume for placental accreta spectrum a year in the weighted model is shown. SV, annualized relative hospital surgical volume for cesarean hysterectomy.

2. Prior Figure 2 was incorrect and the results of revised relative surgical volume cutpoint analysis for the measured surgical morbidity, predefined as haemorrhage, coagulopathy, shock, urinary tract injury, and death are shown in corrected Figure 2 below. Relative hospital surgical volume of 25 cases or more was associated with a statistically significantly lower rate of surgical morbidity (56.7% vs. 63.6%, p = 0.002). Based on this, patients in the study population were grouped into the following three strata: 2705 (45.0%) patients who had caesarean hysterectomy at centers where the relative hospital surgical volume was five cases a year (low-volume group); 2820 (46.9%) patients who had caesarean hysterectomy at centers where the relative hospital surgical volume was more than five but less than 25 cases a year (mid-volume group); and 485 (8.1%) patients who had caesarean hysterectomy at centers where the relative hospital surgical volume 25 cases or more a year (high-volume group).

FIGURE 2

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Association between relative cesarean hysterectomy hospital volume and surgical morbidity. A total of 11 models were tested to examine the association between relative hospital cesarean hysterectomy volume and measured surgical outcomes (hemorrhage, shock, coagulopathy, urinary tract injury, and death): linear, logarithmic, inverse, quadratic, cubic, power, compound, S, logistic, growth, and exponential. Among the statistically significant models, the model exhibiting the minimum p-value was chosen for the analysis (cubic model, p = 6 × 10⁻⁵). In automated fashion, the reflection point was determined by the cubic curve modeling for the cutpoint (≥25 cases, p = 0.002). According the selected model, the surgical morbidity rates are shown per the cutpoint. Dots represent the observed value and bars represent standard error. All the analyses were based on weighted model for national estimates.

3. Prior Table 1 was incorrect and the patient-level characteristics according to the revised exposure grouping are shown in corrected Table 1 below. Compared to the patients in the low-volume group, patients in the mid-volume and high-volume groups were more likely to have medical comorbidity and more severe forms of placenta accreta spectrum. Patients in the mid-volume and high-volume groups were also more likely to have placenta accreta spectrum with placenta previa, a surrogate for antenatally suspected cases, compared to those in the low-volume group.

TABLE 1. Patient demographics per cesarean hysterectomy volume (multivariable analysis).

Characteristic	Low	Mid	High	Mid vs. low	High vs. low
	(%)	(%)	(%)	aOR (95%CI)	aOR (95%CI)
Age (years)	34†	34†	33†	1.01 (1.00–1.02)	0.97 (0.95–0.99)*
Year
2016	32.0	31.4	25.8	1.00 (reference)	1.00 (reference)
2017	31.1	32.8	34.0	1.11 (0.97–1.28)	0.80 (0.62–1.03)
2018	37.0	35.8	40.2	1.15 (1.00–1.32)	0.79 (0.61–1.03)
Race/ethnicity
White	43.1	39.2	33.0	1.00 (reference)	1.00 (reference)
Black	15.5	19.7	22.7	1.33 (1.13–1.58)*	1.73 (1.28–2.35)*
Hispanic	24.4	25.5	27.8	1.37 (1.17–1.60)*	1.47 (1.09–1.98)*
Asian	6.7	5.0	5.2	0.82 (0.63–1.07)	0.84 (0.51–1.37)
Others	5.9	7.1	a	1.46 (1.14–1.88)*	0.46 (0.23–0.92)*
Unknown	4.4	3.5	9.3	1.12 (0.83–1.52)	4.33 (2.71–6.91)*
Primary expected payer
Medicaid	49.9	50.0	53.6	1.00 (reference)	1.00 (reference)
Private including HMO	44.2	43.8	35.1	1.14 (0.84–1.54)	0.96 (0.74–1.24)
Self-pay	2.2	2.3	a	1.41 (0.94–2.11)	0.54 (0.19–1.54)
Others**	3.7	3.9	10.3	1.05 (0.92–1.21)	4.59 (2.95–7.12)*
Median household income
1st QT (lowest)	29.4	29.8	32.0	1.00 (reference)	1.00 (reference)
2nd QT	26.1	24.1	26.8	0.91 (0.78–1.07)	0.84 (0.63–1.11)
3rd QT	22.0	22.9	17.5	1.19 (1.01–1.41)	0.86 (0.62–1.19)
4th QT (highest)	20.3	22.0	23.7	1.13 (0.94–1.36)	1.18 (0.85–1.65)
Unknown	2.2	1.2	0	0.62 (0.39–1.01)	n/a
Obesity
No	83.2	79.8	73.2	1.00 (reference)	1.00 (reference)
Yes	16.8	20.2	26.8	1.17 (1.01–1.37)*	1.61 (1.24–2.09)*
Diabetes mellitus
No	84.1	84.9	73.2	1.00 (reference)	1.00 (reference)
Yes	15.9	15.1	26.8	0.84 (0.71–0.99)*	1.78 (1.37–2.31)*
Hypertensive disease
No	83.2	83.7	73.2	1.00 (reference)	1.00 (reference)
Yes	16.8	16.3	26.8	0.91 (0.78–1.07)	1.59 (1.22–2.07)*
Prior cesarean delivery
No	27.2	23.9	19.6	1.00 (reference)	1.00 (reference)
Yes	72.8	76.1	80.4	1.11 (0.97–1.27)	1.31 (1.01–1.71)*
Placenta previa
No	52.1	43.3	40.2	1.00 (reference)	1.00 (reference)
Yes	47.9	56.7	59.8	1.37 (1.22–1.54)*	1.58 (1.26–1.97)*
PAS type
Accreta	78.6	74.1	70.1	1.00 (reference)	1.00 (reference)
Increta	10.7	12.6	13.4	1.21 (1.01–1.44)*	1.14 (0.83–1.58)
Percreta	10.7	13.3	16.5	1.24 (1.03–1.49)*	1.56 (1.15–2.12)*
Hospital bed capacity
Small	12.8	5.5	0	1.00 (reference)	1.00 (reference)
Medium	30.7	14.4	7.2	1.03 (0.82–1.30)	n/a
Large	56.6	80.1	92.8	3.79 (3.07–4.68)*	n/a
Hospital teaching status
Non-urban teaching	21.3	6.4	0	1.00 (reference)	1.00 (reference)
Urban teaching	78.7	93.6	100	2.11 (1.92–2.32)*	n/a
Hospital region
Northeast	17.6	20.4	25.8	0.81 (0.69–0.95)*	1.31 (0.98–1.77)
Midwest	21.3	18.3	5.2	0.56 (0.47–0.66)*	0.13 (0.08–0.20)*
South	34.9	40.4	28.9	1.00 (reference)	1.00 (reference)
West	26.2	20.9	40.2	0.58 (0.50–0.69)*	1.50 (1.13–1.99)*

• Note: Percentage values per group are shown except for age († median). Annualized relative hospital cesarean hysterectomy volume: low-volume (5 cases), mid-volume (>5 but <25 cases), and high-volume (≥25 cases). A multinomial regression model was used for analysis to examine the difference in characteristics across the 3 groups, and effect size with aOR and corresponding 95%CI is shown in comparison to the low-volume group. **included Medicare, no charge, other, and unknown.
• Abbreviations: aOR, adjusted odds ratio; CI, confidence interval; QT, quartile; and PAS, placenta accreta spectrum.
• ^a Suppressed per the HCUP guidelines.
• * p < 0.05.

4. Prior Table 2 was incorrect and the results of revised volume-outcome relationship are shown in corrected Table 2 below. Patients in the high-volume group were 23% less likely to have the measured surgical morbidity compared to those in the low-volume group (56.7% vs. 62.7%, adjusted-odds ratio 0.77, 95% confidence interval 0.62–0.96) in multivariable analysis. This association remained when patients in the high-volume group were compared to those in the mid-volume group (56.7% vs. 64.5%, adjusted-odds ratio 0.73, 95% confidence interval 0.60–0.91).

TABLE 2. Surgical morbidity per cesarean hysterectomy volume (multivariable analysis).

Characteristic	(%)	aOR (95%CI)
Hospital surgical volumea
Low-volume	62.7	1.00 (reference)
Mid-volume	64.5	1.05 (0.93–1.18)
High-volume	56.7	0.77 (0.62–0.96)*
Age (years)	—	0.99 (0.98–1.00)
Year
2016	66.4	1.00 (reference)
2017	63.5	0.89 (0.78–1.03)
2018	59.9	0.77 (0.67–0.88)*
Race/ethnicity
White	63.0	0.83 (0.71–0.96)*
Black	62.2	1.02 (0.85–1.22)
Hispanic	65.0	1.00 (reference)
Asian	68.1	1.04 (0.80–1.36)
Others	50.0	0.62 (0.48–0.78)*
Unknown	67.9	0.93 (0.70–1.25)
Primary expected payer
Medicaid	59.9	1.00 (reference)
Private including HMO	65.6	1.42 (1.24–1.62)*
Self-pay	76.9	2.37 (1.53–3.67)*
Others	67.3	1.61 (1.21–2.15)*
Median household income
1st QT (lowest)	59.2	1.00 (reference)
2nd QT	69.0	1.57 (1.35–1.82)*
3rd QT	58.9	0.85 (0.73–0.99)*
4th QT (highest)	64.6	1.11 (0.94–1.32)
Unknown	78.9	2.35 (1.39–3.98)
Obesity
No	63.6	1.00 (reference)
Yes	60.6	0.95 (0.82–1.10)
Diabetes mellitus
No	64.1	1.00 (reference)
Yes	57.9	0.82 (0.70–0.95)*
Hypertensive disease
No	64.9	1.00 (reference)
Yes	54.5	0.74 (0.64–0.85)*
Prior cesarean delivery
No	64.8	1.00 (reference)
Yes	62.5	0.83 (0.73–0.95)*
Placenta previa
No	53.1	1.00 (reference)
Yes	71.9	2.33 (2.08–2.60)*
PAS type
Accreta	63.3	1.00 (reference)
Increta	62.7	0.94 (0.79–1.12)
Percreta	61.7	0.98 (0.83–1.16)
Hospital bed capacity
Small	62.0	1.00 (reference)
Medium	62.2	0.98 (0.78–1.23)
Large	63.4	1.00 (0.82–1.23)
Hospital teaching status
Non-urban teaching	64.2	1.00 (reference)
Urban teaching	62.9	0.96 (0.81–1.15)
Hospital region
Northeast	59.1	1.00 (reference)
Midwest	66.8	1.42 (1.18–1.71)*
South	62.7	1.25 (1.07–1.45)*
West	63.9	1.20 (1.02–1.43)*

• Note: A binary logistic regression model for multivariable analysis to examine the association between surgical volume and predetermined surgical complications (hemorrhage, shock, coagulopathy, urinary tract injury, and death). High-volume group was also associated with 27% decreased risk of surgical complication compared to mid-volume group (aOR 0.73, 95% CI 0.60–0.91).
• Abbreviations: aOR, adjusted-odds ratio; and CI, confidence interval.
• ^a Annualized relative hospital cesarean hysterectomy volume: low-volume (5 cases), medium-volume (>5 but <25 cases), and high-volume (≥25 cases).
• * p < 0.05.