The study's objective was to identify HPA 1a-negative women and to offer them an intervention program aimed to reduce morbidity and mortality of neonatal alloimmune thrombocytopenia (NAIT). HPA 1 typing was performed in 100 448 pregnant women. The HPA 1a-negative women were screened for anti-HPA 1a. In immunized women, delivery was performed by Cesarean section 2 to 4 weeks prior to term, with platelets from HPA 1a-negative donors reserved for immediate transfusion if petechiae were present and/or if platelet count was less than 35 x 10(9)/L. Of the women screened, 2.1% were HPA 1a negative, and anti-HPA 1a was detected in 10.6% of these. One hundred seventy pregnancies were managed according to the intervention program, resulting in 161 HPA 1a-positive children. Of these, 55 had severe thrombocytopenia (< 50 x 10(9)/L), including 2 with intracranial hemorrhage (ICH). One woman with a twin pregnancy missed the follow-up and had one stillborn and one severely thrombocytopenic live child. In 15 previous prospective studies (136 814 women) there were 51 cases of severe NAIT (3 intrauterine deaths and 7 with ICH). Acknowledging the limitation of comparing with historic controls, implementation of our screening and intervention program seemed to reduce the number of cases of severe NAIT-related complications from 10 of 51 to 3 of 57.