To explore the correlation between Doppler parameters of the fetal primary pulmonary artery and gestation age in normal fetuses.

Three hundred normal fetuses at gestational ages of 21-40 weeks were divided into ten groups according to gestational age: 21-22^{+ 6} weeks, 23-24^{+ 6} weeks, 25-26^{+ 6} weeks, 27-28^{+ 6} weeks, 29-30^{+ 6} weeks, 31-32^{+ 6} weeks, 33-34^{+ 6} weeks, 35-36^{+ 6} weeks, 37-38^{+ 6} weeks, and 39-40^{+ 6} weeks, with 30 cases in each group. Doppler parameters of the fetal primary pulmonary artery were measured using a color ultrasound system, including acceleration time (AT), ejection time (ET), peak systolic velocity (PSV), end diastolic velocity (EDV), mean velocity (MV), pulsatility index (PI), and resistance index (RI). The normal reference values of Doppler parameters of the fetal primary pulmonary artery at different gestation ages were established, and correlation and regression analyses of the parameters and gestation age were made.

Satisfactory primary pulmonary artery flow velocity curves were obtained in all the 300 fetuses. Among the parameters detected, AT, AT/ET, PSV, EDV, and MV increased and PI decreased with increasing gestational age (P<0.05), while ET and RI had no significant changes (P>0.05). AT, AT/ET, PSV, EDV, and MV of the fetal primary pulmonary artery were significantly positively correlated with gestational age (r=0.866, 0.848, 0.457, 0.242, and 0.506, respectively, P<0.05), PI was negatively correlated with gestational age (r=-0.170, P<0.05), and ET and RI had no correlation with gestational age (r=0.195 and -0.197, respectively, P>0.05).

Doppler parameters have a correlation with gestational age in normal fetuses, among which AT and AT/ET have the best correlation.