Chołubek, Gustaw, Krzysztof Wiktor, Dorota Robak-Chołubek, Lechosław Putowski, and Henryk Wiktor. 2012. “Ultrasound in Obstetrics – More Safe?”. Polish Journal of Public Health 122 (1): 100-103. https://czasopisma.umlub.pl/pjph/article/view/1545.