OBJECTIVES Chronic co-morbid conditions during pregnancy have been associated with poor maternal and infant health. Although studies have shown that women with anemia, diabetes or thyroid dysfunction during pregnancy are at high risk of complications in delivery, little is known about their impact on the length of hospitalization. The objective of this study was to identify the increased Length of Stay (LOS) of pregnant women with these high-risk comorbidities compared with other comorbidities, hospitalized for delivery and labor in the US. METHODS The 2006 National Hospital Discharge Survey (NHDS) was used as data source for the study. ICD-9-CM codes were reviewed to extract records of women with comorbid complications during labor and delivery (660.0 – 669.9) and to further identify women with high-risk comorbidity of anemia (648.0), diabetes (648.2) or thyroid dysfunction (648.1) complicating pregnancy, childbirth, and the puerperium. Survival analysis alongwith log rank test was used to evaluate the differences of LOS between patients with high risk comorbidities and low risk comorbidities. RESULTS The 2006 NHDS recorded data for a total of 23,941 women with complications in delivery and labor. Among these, 2,490 women had high risk comorbidities while 21,451 women had other comorbidities complicating their delivery and labor. The median LOS for women with high risk comorbidities (3 days) was 1 day higher compared to pregnant women with other co-morbidities (2 days; p = 0.001). CONCLUSIONS This study provides empirical data on LOS for women with high risk comorbidities in the course of labor and delivery. This result can be used as a basis by hospitals to assess their precautionary guidelines in pregnant women with high risk comorbidities to avoid additional LOS. Further research can be performed to investigate the impact of demographic characteristics and source of payment on the LOS of pregnant women with high risk comorbidities.