Supplementary Table 1.

International Classification of Diseases, Ninth Edition, Clinical Modification (ICD-9-CM) codes for identifying pregnancy-related hospitalization (where only 3 or 4-digit codes are listed, all associated subcodes are included).

Category	ICD-9-CM codes
Pregnancy with abortive outcome	630–639.9
Complications mainly related to pregnancy	640–648.9
Normal delivery and other indications for care in pregnancy labor and delivery	650–659.9
Complications occurring during mainly the course of labor and delivery	660–666.9
Complications of the puerperium	670–676.9
Outcome of delivery	V27.0–V27.9