Objective To explore the change of Doppler velocity waveforms in the fetal main pulmonary artery in patients with early onset severe preeclampsia and to assess its value in fetal lung maturity.Methods A prospective study was conducted to analyze fetal main pulmonary artery velocity waveforms parameters including acceleration time(AT),ejection time(ET),acceleration time/ejection time (AT/ET),peak systolic velocity (PSV) in 30 cases of pregnant women with early onset severe preeclampsia.According to neonatal outcome,these cases were divided into respiratory distress syndrome (RDS) group (18 cases) and non-RDS group (12 cases).Each group was compared with 54 cases and 36 cases that were normal and had corresponding gestational age separately.Doppler parameters were compared between these two groups and their corresponding normal control groups.Results Gestational age at sonographic examination,gestational age at delivery and birth weight of neonates in RDS group were significantly lower than those in non-RDS group(all P ＜0.001).The value of AT,ET,AT/ET,PSV were lower in RDS group than those in gestational age-matched control group(all P ＜0.05),while there were no significant difference between non-RDS group and gestational age-matched control group(all P ＞ 0.05).Conclusions Doppler ultrasound monitoring fetal main pulmonary artery velocity waveforms to evaluate fetal lung maturity in patients with early onset severe preeclampsia has clinical application value.