Astrika, Gemini, Ardi Panggayuh, & Tri Mardiyanti. " The Effect Of Birthing Ball On The Duration Of Active Phase In Primigravida At Pmb Yulis Indriana, Malang." Jurnal Pendidikan Kesehatan (e-Journal) [Online], 8.2 (2019): 164 - 175. Web. 15 Aug. 2020