Study objective: To study secular trends of placental abruption (PA), the effects of demographic variables and the use of cesarean section (CS) associated with PA.
Design: A population based cohort study.
Setting: The Medical Birth Registry of Norway.
Patients: 9,592 cases of PA of a total of 1,446,154 births notified, i.e. all births in Norway 1967-1991.
Main results: The PA proportion was 6.6 per 1000 births of a gestational age of 16 weeks or more, ranging from 5.3 in 1971 to 9.1 in 1990. Birth order two had the lowest proportion and it increased by maternal age. The PA proportion decreased by gestational age from 86.4 per 1000 below 28 weeks to 3.4 in term pregnancies. The PA proportion per 10,000 pregnancies at risk increased from 1.3 in the 28th week to 14.1 in the 42nd week. A secular trend of a decreasing but still high relative risk of PA in SGA-births at any gestational age increased from 1967 through 1991. The relative risk of PA of Apgar score <7 after five minutes, adjusted for gestational age, was 7.8.
Conclusions: Inspite of an increasing CS rate, an increasing proportion of PA was noted from 1967 through 1991. The proportion was lowest for birth order two and increased by maternal age. To an increasing extent, PA births were centralized. SGA, prematurity and asphyxia were major problems associated with PA. A tendency towards larger infants and a decreasing relative risk of PA in SGA-births might be attributable to improvements in antenatal care.