3. Hematocrit level under 30% accompanied by clinical signs of severe anemic. Auditory Evoked Potential All newborns involved in the study will undergo a non-invasive hearing test, at the occasion of hospital discharge or at the first time they go to the ambulatory for follow-up. The application of the hearing evoked potential is indicated to all isoimmunized newborns and is routinely performed at the local where the study is taking place.