Pengaruh asfiksia terhadap kualitas hidup anak usia 2-4 tahun ; studi kohort retrospektif bayi prematur periode tahun 2011-2013 di Yogyakarta = Effect of asphyxia on the quality of life of children aged 2-4 years retrospective cohort study of premature infants period of 2011- 2013 in Yogyakarta