Longitudinal study of the association between thrombocytopenia and retinopathy of prematurity.

BACKGROUND:An association between thrombocytopenia and retinopathy of prematurity (ROP) has been suggested but not been studied longitudinally. We sought to identify the time period in postnatal development during which thrombocytopenia and the subsequent development of severe ROP are associated. METHODS:This was a retrospective case-control study of 100 subjects who received laser photocoagulation for type 1 ROP between 2005 and 2009 and 100 controls with no ROP or only stage 1 ROP. The proportions of infants with thrombocytopenia, defined as a serum platelet level of <150,000/μL, among cases versus controls were compared on a weekly basis from birth through the time of laser during early (postmenstrual age [PMA] weeks 24-28), middle (PMA weeks 29-34), and late (PMA weeks 35-38) time periods. Main outcome measures were odds ratios for the association between thrombocytopenia and type 1 ROP from multivariate logistic regression models adjusted for gestational age, birth weight, culture-proven sepsis, and necrotizing enterocolitis. RESULTS:Thrombocytopenia was significantly associated with severe ROP during PMA weeks 24-28 (adjusted OR, 4.7; 95% CI, 2.0-1.1; P = 0.001) and 29-34 (adjusted OR, 2.8; 95% CI, 1.4-5.6; P = 0.006), but not during weeks 35-38 (adjusted OR, 2.0; 95% CI, 0.9-4.3; P = 0.10). CONCLUSIONS:Thrombocytopenia from birth through 34 weeks' PMA was associated with subsequent severe ROP. This time period corresponds to a period of poor retinal vascular growth, suggesting a possible proangiogenic effect of platelets in normal retinal vascular development in infants at risk for ROP.