Background: Transient tachypnea of the newborn (TTN) is a benign, self-limited condition that can present in full‐term or late preterm infants. TTN is caused by delay in clearance of fetal lung fluid after birth.
Objective: To evaluate the role of platelet mass index (PMI) in predicting the severity of transient tachypnea of newborn (TTN).
Patient and methods: This was a case control study followed by follow up of cases till remission of TTN. It was carried out on 100 term and near-term neonates with TTN. Platelet mass index (PMI) test was done by CBC which included platelet count, as well as platelets indices such as mean platelets (MPV) in neonatal intensive care unit at Damietta, Al-Azhar University Hospital. PMI was calculated using the following formula: PMI = platelet count x mean platelet volume /103 (fl/nl).
Results: Decreased platelet count and PMI were significantly associated with TTN when compared to control group. Increased duration of oxygen therapy was significantly associated with decreasing platelet count and PMI.  MPV did not differ significantly between cases and controls as well as according to duration of oxygen therapy. Platelet count and PMI showed significant increase after remission. PMI showed significant positive correlations with platelet count, and significant negative correlations with duration of oxygen therapy. No significant correlations were found regarding of PMI with other parameters among studied TTN cases.
Conclusion: Lower PMI and platelet count were associated with longer duration of oxygen therapy in patient with TTN, which could be used in prediction of severity of TTN.