Background: It is common to admit to hospital or start intensive ambulatory antenatal care of pregnant women with a previous placental abruption using the gestational age of the previous placental abruption as a starting point. In some instances, close surveillance may be commenced much earlier. There is no consensus when in a subsequent pregnancy such measures should be initiated.
Objective: The analyses aimed at the prevention of complicated (preterm, small for gestational age, or perinatal death) recurrent placental abruptions, assessing at which time in a subsequent pregnancy special surveillance should start in order to anticipate and prevent a recurrence.
Design: A cohort study based on the Medical Birth Registry of Norway. Calculation of gestational age specific risks of placental abruption in a second pregnancy and estimation of when to initiate surveillance in order to reduce an increased risk of recurrent placental abruption to the initial level of initial abruption in the second pregnancy.
Results: In women with a complicated (preterm, small for gestational age, or perinatal death) first delivery, the risks of an initial and recurrent complicated placental abruption in the second pregnancy were 7/1000 and 33/1000, respectively (relative risk 4.9). To reduce the recurrence risk in a second pregnancy to 7/1000, special surveillance six weeks prior to the gestational age of the initial abruption would be necessary. In women with an uncomplicated first delivery, the risks in the second pregnancy of an initial and recurrent complicated abruption were 3 and 19/1000, respectively (relative risk 7.1). To reduce the recurrence risk to 3/1000, surveillance at least 12 weeks prior would be necessary.
Conclusion: The increased recurrence rate would necessitate increased awareness in terms of special surveillance in the second pregnancy. In pregnancies at risk of a recurrent placental abruption, monitoring up to three months before the gestational age of the initial abruption is necessary.