Identifying spontaneous PTB risk
For women without a GA code in their records, the distinction of sPTB was made by codes for preterm labor with preterm delivery (ICD-9 code 644.21; ICD-10 codes O60.1*X0, O42.012). For women with a GA code, sPTB was identified by a GA code <37 weeks accompanied by a code for the following diagnoses:
1. premature rupture of membranes (ICD-9 codes 658.1; ICD-10 codes O42.012, O42.013, O42.019, O42.112, O42.113, O42.119, O42.9 except O42.911);
2. early or threatened preterm labor (ICD-9 codes 644.*; ICD-10 codes O60.1*X0, O60.0).