Maternal thrombocytopenia at term: a population-based study

Thrombocytopenia is a common problem during pregnancy and often inappropriately managed. This study aimed to assess the prevalence and causes of maternal thrombocytopenia at term with special attention to immune mechanisms of thrombocytopenia and the need for assessing fetal risks.

We conducted a 1-year population-based surveillance study involving 4,382 fullterm (at least 37 weeks' gestation) women (83.8% of the study population) and their infants from the city of Helsinki. Maternal and cord platelet counts were performed at delivery. Immune studies were performed if maternal platelet counts were less than 100 x 10(9)/l; 95% confidence intervals (CIs) were calculated from the binomial distribution.

A total of 317 women (7.3%; 95% CI 6.5, 8.1) had platelet counts of less than 150 x 10(9)/l. Most cases (81%) of maternal thrombocytopenia at term were due to gestational thrombocytopenia, which had no impact on either the mother or the fetus unless associated with some other medical or obstetric disorder. Other causes of thrombocytopenia were preeclampsia (16%) and idiopathic thrombocytopenic purpura (ITP) (3%). There was no association between maternal and fetal platelet counts: of the infants born to thrombocytopenic mothers, 2.1%, had thrombocytopenia in the cord blood, which did not differ significantly from the 2.0% of thrombocytopenic infants born to non-thrombocytopenic mothers.

Women with gestational thrombocytopenia do not require alteration of their treatment. Fetal blood sampling is not considered necessary when thrombocytopenia is discovered unexpectedly at term.