Jane Bendix, Hanne Kristine Hegaard, Jens Langhoff-Roos, Thomas Bergholt

Population-based studies evaluating the use and extent of antenatal obstetric hospitalizations (AOH) are sparse. The objective of the present study was to describe the prevalence, time trend, and risk factors for AOH in Denmark. A retrospective national register-based cohort study was conducted that included all pregnancies with delivery after 22 gestational weeks in Denmark from 2003 to 2012. The outcomes were AOH and the diagnoses leading to these hospitalizations. AOH was defined as an antenatal hospitalization for at least 1 day with at least one obstetric International Classification of Diseases-10 diagnosis and admission date more than 3 days before delivery. The study included 617,906 pregnancies; 48,366 (7.8%) pregnancies were associated with 64,072 AOH before delivery. The percentage of pregnancies with AOH decreased from 8.6% to 7.1%. The median length of stay decreased from 3 to 2 days, and admission for at least 7 days was almost halved. Threatened preterm delivery was the most frequent diagnostic category for AOH. A decline was seen in all diagnostic categories except maternal diseases. Significant risk factors for AOH were multiple pregnancies, low or high maternal age and body mass index, nulliparity, lower educational levels, unemployment or being outside the workforce, single partner status, and smoking. The relative risk of very preterm delivery before gestational age of 34 weeks was higher in pregnancies with AOH compared with pregnancies without AOH (relative risk 15.2; 95% confidence interval: 14.6-15.8). This study shows a shift toward less use and shorter duration of antenatal hospitalization in Denmark. The most common indication used in pregnancies with AOH was threatened preterm delivery, and more than one-third resulted in very preterm deliveries.