case ascertainment and detailed clinical information,
some outcome events may have represented
delayed sequelae of previous thrombotic events.
For example, an outpatient in whom venous
thromboembolism is diagnosed at 2 weeks after
delivery who is then hospitalized with symptoms
of venous thromboembolism 8 weeks later would
have incorrectly appeared to have had a first
thrombotic event at 10 weeks after delivery.