Thrombocytopenia in term infants: a population-based study.

Objective: To assess the prevalence and causes of thrombocytopenia among full-term infants.

Methods: We conducted a 1-year, population-based surveillance study involving all full-term infants (at least 37 weeks' gestation) born to native Finnish women in Helsinki. In cases of thrombocytopenia (cord platelet count less than 150 x 10(9)/L) clinical risk factors were evaluated and immunologic studies were performed on both parents and on the infant; 95% confidence intervals (CIs) were calculated on the basis of binomial distribution.

Results: Platelet counts were done in cord blood from 4,489 infants, 84.9% of the study population. Eighty-nine infants had platelet counts below 150 x 10(9)/L (2.0%; 95% CI 1.5, 2.3) in cord blood and 11 were less than 50 x 10(9)/L (0.24%; 95% CI 0.10, 0.38). All causes of clinically important thrombocytopenia, those presenting with bleeding and requiring treatment, were related to fetomaternal alloimmune thrombocytopenia. The incidence of severe alloimmune thrombocytopenia was one in 1500 live births and one in 900 of all thrombocytopenia. An immunologic mechanism was involved in ten of 65 (15.4%; 95% CI 6.6, 24.2) infants studied and in four of 15 (26.7%; 95% CI 4.3, 49.1) cases of severe thrombocytopenia.

Conclusion: Immunologic studies should be considered in all cases of severe neonatal thrombocytopenia for careful monitoring and prevention of potentially severe complications in subsequent pregnancies.