All women were white and of European background. Subsequent
pregnancy follow-up revealed that 63 (19.9%) of the
subjects had either an elective pregnancy termination or a complicating
pregnancy factor that placed them at risk for an adverse
outcome: placenta praevia, intrauterine growth restriction,
hypertension, cervical incompetence, or twin gestation.
The remaining 254 women had no known risk factor for adverse
pregnancy outcome.