Identification of response bias on apparent pregnancy outcome after second trimester ultrasound.

Objectives: To investigate whether there is a response bias in outcome studies after prenatal ultrasound and to quantify this potential effect by information source.

Materials And Methods: All normal ultrasound scans between week 17 and week 24 and 6 days performed in the years 2004 and 2005 were investigated. A multinomial logistic regression model was applied to investigate the association between responders' outcome (questionnaire, phone interview and inquiry to birth clinic) and the following explanatory variables: maternal age, smoking status, body mass index, congenital anomaly status, low birthweight and preterm deliveries.