Blood flow velocity waveforms from fetal peripheral pulmonary arteries in pregnancies with preterm premature rupture of the membranes: relationship with pulmonary hypoplasia

Abstract

Objectives: To measure fetal peripheral pulmonary artery velocity waveforms by Doppler ultrasonography in pregnancies complicated by premature rupture of membranes under 24 weeks' gestation and to relate the Doppler indices to the development of fetal pulmonary hypoplasia.

Design: A prospective longitudinal study of fetal peripheral pulmonary artery velocity waveforms from premature rupture of membranes to delivery.

Subjects: Twenty pregnancies complicated by premature rupture of membranes before 24 weeks of gestation and delivering after 26 weeks.

Methods: Peripheral pulmonary artery velocity waveforms were recorded by Doppler technique at weekly intervals until delivery and Pulsatility Index (PI) calculated. Pregnancies were managed conservatively according to an institutional management protocol. Pulmonary hypoplasia was defined at autopsy by lung/body weight ratios and radial alveolar counts. Pulsatility Indices of fetuses developing pulmonary hypoplasia were compared with those with a normal lung development.

Results: After premature rupture of membranes PI values were higher than normal reference limits for gestation, but no differences were found between the six fetuses which developed pulmonary hypoplasia and the remaining 14 fetuses with normal lung development. In this latter group PI values progressively decreased with advancing gestation (ANOVA for repeated measurements F = 11.61; P < or = 0.001), while they increased in fetuses developing pulmonary hypoplasia (F = 8.44; P < or = 0.001). As a consequence of these opposite trends significant differences in PI values were present between the two groups of fetuses from 2 weeks after the premature rupture of membranes. Two weeks after the premature rupture of membranes a PI value from the peripheral pulmonary arteries above the 95th centile had a sensitivity of 62.5%, specificity of 94.6%, positive predictive value of 83.3%, negative predictive value of 78.5% and relative risk of 3.88 (95th confidence interval 1.34-11.28) for the prediction of pulmonary hypoplasia.

Conclusion: The measurement of peripheral pulmonary velocity waveforms may help to establish the risk of developing pulmonary hypoplasia in pregnancies complicated by premature rupture of membranes.