Alexander Butwick

Background The 10th revision of the International Classification of Diseases, Clinical Modification (ICD‐10) includes diagnosis codes for placenta accreta spectrum for the first time. These codes could enable valuable research and surveillance of placenta accreta spectrum, a life‐threatening pregnancy complication that is increasing in incidence. Objective We sought to evaluate the validity of placenta accreta spectrum diagnosis codes that were introduced in ICD‐10 and assess contributing factors to incorrect code assignments. Methods We calculated sensitivity, specificity, positive predictive value and negative predictive value of the ICD‐10 placenta accreta spectrum code assignments after reviewing medical records from October 2015 to March 2020 at a quaternary obstetric centre. Histopathologic diagnosis was considered the gold standard. Results Among 22,345 patients, 104 (0.46%) had an ICD‐10 code for placenta accreta spectrum and 51 (0.23%) had a histopathologic diagnosis. ICD‐10 codes had a sensitivity of 0.71 (95% CI 0.56, 0.83), specificity of 0.98 (95% CI 0.93, 1.00), positive predictive value of 0.61 (95% CI 0.48, 0.72) and negative predictive value of 1.00 (95% CI 0.96, 1.00). The sensitivities of the ICD‐10 codes for placenta accreta spectrum subtypes— accreta, increta and percreta—were 0.55 (95% CI 0.31, 0.78), 0.33 (95% CI 0.12, 0.62) and 0.56 (95% CI 0.31, 0.78), respectively. Cases with incorrect code assignment were less morbid than cases with correct code assignment, with a lower incidence of hysterectomy at delivery (17% vs 100%), blood transfusion (26% vs 75%) and admission to the intensive care unit (0% vs 53%). Primary reasons for code misassignment included code assigned to cases of occult placenta accreta (35%) or to cases with clinical evidence of placental adherence without histopatholic diagnostic (35%) features. Conclusion These findings from a quaternary obstetric centre suggest that ICD‐10 codes may be useful for research and surveillance of placenta accreta spectrum, but researchers should be aware of likely substantial false positive cases.