* Identification of response bias on apparent pregnancy outcome after second trimester ultrasound. Kozlowski P, Stressig R, Hammer R, Siegmann HJ, Froehlich S, Verde PE, Knippel AJ. Prenat Diagn. 2011 Aug;31(8):750-4
* Individual risk of fetal loss following routine second trimester amniocentesis: a controlled study of 20,460 cases. Kozlowski P, Knippel A, Stressig R. Ultraschall Med. 2008 Apr;29(2):165-72.