15-year evaluation of changes in the HBsAg positivity rate in pregnant women in Turkey: the prominent effect of national vaccinationSelma Tosun, Ayşegül Erdoğan, Ayşe Torun, Selma Sever, Sibel Altuntas, İlknur Yildiz, Hüseyin Kutlu, Mehmet Ceylan, Pembe Yesilbag, Bayhan Bektore, Nefise Oztoprak, Buket Gungor, Sezen Koparan, Gülnur Kul, Ali Olut, Bülent Altuntaş and Multicenter Study G