Exploration Of The Changes Of Cardiac Output And Distribution With Advancing Gestational Age In Normal Fetuses Of Middle And Late Pregnancy By Ultrasonic Technique

Objective: To investigate the changing tendencies of cardiac outputs of left,right ventricular,combined cardiac output and blood flow of foramen ovale,ductus arteriosus and aorta isthmus,and their distribution law in different parts of the body of middle and late pregnancy in normal fetal with advancing gestational age by ultrasonic technique,and established the normal reference ranges of fetal cardiac output in different weeks of gestation.It would help to understand the situation of fetal circulatory system and provide guidance for clinical early identification of fetal abnormalities.Methods : One hundred and eighteen pregnancies with a gestational age of 20 ~ 40 weeks underwent conventional ultrasound and fetal echocardiography respectively.For purposes of analysis,fetuses were divided into 5 groups respectively with gestational age,group 1: 20 to 24 weeks(n = 23),group 2: 24+1to 28 weeks(n = 24),group 3: 28+1to 32 weeks(n = 24),group 4: 32+1to 36 weeks(n = 25),group 5: 36+1to 40 weeks(n =22).Pregnant women in the supine position(or in the lateral position if uncomfortably).Firstly,conventional ultrasound was performed for understanding the situation of fetal different organs,placenta,amniotic fluid and so on to exclude fetal extracardiac structural abnormalities;to measure fetal biparietal diameter,head circumference,abdominal circumference and femur length in obstetric condition,and record the fetal body weight and gestational week which the system automatically generate.Next,switch to the fetal cardiac ultrasound conditions and commencemeasuring the fetal heart related parameters,including the largest diameters of aortic artery,pulmonary artery,ductus arteriosus,aortic isthmus,respectively in the left ventricular outflow view,right ventricular outflow view or three vessels view,ductal arch long-axis view and aortic arch longitudinal view.In addition,the diameter of foramen ovale is measured in the four chamber view,which is in the middle of atrial septal.The blood flow spectrums of these parts were acquired in these views and its VTI(Velocity time integral)and HR(Heart rate)were got by envelope model manually.Finally,applying the formula Q(Quantity of flow)=(D/2)2 x 3.14 x VTI x HR for calculating cardiac outputs of left ventricular and right ventricular,combined cardiac output and blood flow of ductus arteriosus,aortic isthmus and foramen ovale.Results: The cardiac outputs of left and right ventricle,combined cardiac output,the blood flow of aortic isthmus,ductus arteriosus and foramen ovale in normal fetuses of middle and late pregnancy gradually increase with the increasing of gestational age,and there are exponential curve correlation between output of these parts and gestational age;right ventricular output are larger than left ventricular output in each group,The ratio of right ventricular cardiac output and left ventricular cardiac output increase gradually with advancing gestational age;blood flow of ductus arteriosus are larger than blood flow of aortic isthmus in each group,the ratio of blood flow of aortic isthmus and ductus arteriosus decrease gradually with advancing gestational age;the ratio of aortic isthmus blood flow and combined cardiac output decrease gradually with the increasing pregnancy week;the ratio of ductus arteriosus blood flow and combined cardiac output increase gradually with advancing gestational age;the ratio of right ventricular output and combined cardiac output increase gradually with the increasing pregnancy week;the ratio of left ventricular output and combined cardiac output decrease gradually with the increasing pregnancy week;the ratio of foramen ovale blood flow and combined cardiac output decrease gradually from group 1 to group 3,and there are no obvious change after group 3;the blood flow of aortic isthmus increase gradually with the increasing fetal weight;combined cardiac output index(meaning combined cardiac output / fetal weight)don’t change with the increasing pregnancy week.Conclusion: This study established the normal reference range of cardiac outputs of left and right ventricle,combined cardiac output,the blood flow of aortic isthmus,ductus arteriosus and foramen ovale in normal fetuses,and meanwhile analyzed the distribution of bood flow in different parts of middle and late pregnancy with the increasing of gestational.The findings especially contribute to the understanding of fetal physiological conditions of circulatory system,and improve the prediction and identification of abnormal situation.Above all,this study would provide the forceful basis for assessment of fetal anomalies.