Doppler studies to assess gestational age

Alberto Sosa-Olavarría, MD; Luis Díaz-Guerrero, MD

Unidad de Perinatolog√≠a, Universidad de Carabobo. Ciudad Hospitalaria ‚ÄúDr. Enrique Tejera‚ÄĚ, Valencia, Estado Carabobo, Venezuela.

To demonstrate that the impedance ratio of ductus arteriosus and pulmonary artery could be used as a diagnostic test for preterm, term and post-term pregnancies.


We included 134 pregnant patients, 52 preterm, 65 term and 17 post-term pregnancies. Ductus arteriosus and pulmonary artery blood flow velocity waveforms were investigated in all pregnancies by pulsated-wave Doppler ultrasound.
The study was conducted in Perinatology Unit, Hospitalary City ‚ÄúDr. Enrique Tejera‚ÄĚ, Valencia, Carabobo State, Venezuela between August 1999 and January 2000.


In a sagittal or axial plane we first obtained the pulsed Doppler wave of the ductus arteriosus flow and measured the acceleration time and ejection time in milliseconds obtaining an impedance index (TA/TE). The same measurement was done for the pulsed wave of the pulmonary artery. The ratio between these two values was counted, the ductus  arteriosus impedance index was divided by impedance index of the pulmonary artery. The result was multiplied by 1000 and was called IRIDAPta/te. (Impedance Relative Index between Ductus Arteriosus and Pulmonary artery using acceleration time / ejection time) This procedure which uses a noninvasive tool, reveals a redirection of blood flow from the ductus arteriosus to the pulmonary area as the pregnancy progresses.
This method has been used in our perinatology unit for past eleven years. Since implementation of this method we have not performed amniocentesis to assess lung maturity.


The values of relative impedance index between ductus arteriosus and pulmonary artery in the preterm pregnancies were 1.678 (0.407 SD - standard deviation), in term pregnancies were 1.034 (0.326 SD) and post term pregnancies were 0.882 (0.104 SD). The cutoff point equal or below 1.1 (likelihood ratio of 12.5). All cases (100%) with 42 or more weeks of gestation showed values under 1.0. Chi square value was 30.9 with p< 0.05.


Along the normal pregnancy, ductus arteriosus and pulmonary artery impedance ratio values show opposite tendency patterns. Ductus arteriosus impedance increases towards term as pulmonary impedance decreases. At term, the relative impedance index values are equal or below 1,1 suggesting a circulatory lung hemodynamic changes in accordance with lung maturity. In post-term patients the impedance index values are below 1.0. We recommend the use of this index as a diagnostic tool in the functional assessment of the gestational age.
Images 1, 2: PA pulmonary artery, DA ductus arteriosus, RV right ventricle, Ao aorta, AI aortic isthmus, SA subclavia artery. The red circles show the area of Doppler measurement. Image 1 is a sagittal plane of fetal thorax. Image 2 is the short axis of the pulmonary artery.


Image 3,4: Image 3 shows axial plane of the fetal thorax, power Doppler. Pulsed  Doppler wave of the pulmonary artery and ductus arteriosus showing the measurement of the acceleration time, ejection time and impedance index of each artery. Image 4 shows relationship between the values of the TA/TE (acceleration and ejection time) and gestational age. Acceleration time of the ductus arteriosus (red lines) and the pulmonary artery (blue lines) with the different periods of lung development by gestational age showing the opposite tendency patterns with crossing point at 37 weeks.

Figure 1,2: Figure 1 shows values of TA/TE (acceleration / ejection time) of the ductus arteriosus (red) and pulmonary artery (yellow). Blue bars demonstrate the values of  IRIDAPta/te (impedance relative index between ductus arteriosus and pulmonary artery) showing marked difference between preterm, term and post-term pregnancies. Figure 2 shows distribution of cases according to the cutoff point for both the IRIDAPta/te and  gestational age.



1. Sosa Olavarr√≠a A., D√≠az Guerrero L. √ćndice relativo de impedancia Doppler entre el ductus arterioso y la arteria pulmonar en el embarazo normal, pret√©rmino y post√©rmino. Rev Obstet Ginecol Venez 2000;60(2):97-101.
2. Rizzo G, Caponni A, Arduini D, Romanini C. The value of fetal arterial, cardiac and venous flows in predicting pH and blood gases measured in umbilical blood at cordocentesis in growth retarded fetuses. Br J Obstet Gynaecol 1995;102:963-969.
3. Hecher K, Snijders R, Campbell S, Nicolaides K. Fetal venous, intracardiac and arterial blood flow measurements in intrauterine growth retardation: Relationship with fetal blood gases. Am J Obstet Gynecol 1995;173(1):10-15.
4. DeVore G. Color Doppler examination of the outflow tracts of the fetal heart: A technique for identification of cardiovascular malformation. Ultrasound Obstet Gynecol 1994;4:463-471.
5. Kiserud T, Eik-Nes SH, Hellevik RL, Blaas H-G. Ductus venosus blood velocity changes in fetal cardiac diseases. J Matern Fetal Invest 1993;3:15-20.
6. Matias A, Gomes C, Flack N, Montenegro N, Nicolaides KH. Screening for chromosomal abnormalities at 10-14 weeks: The role of the ductus venosus blood flow. Ultrasound Obstet Gynecol 1998;12:380-384.
7. Borrel A, Antolin E, Costa D, Farre T, Martinez J, Fortuny A. Abnormal ductus venosus blood flow in trisomy 21 fetuses during early pregnancy. Am J
Obstet Gynecol 1998;179:1612-1617.
8. Hislop A, Reid L. Intrapulmonary arterial development during fetal life: Branching pattern and structure. J Anat 1972;113:35-48.
9. Emerson DS, Cartier MS. The fetal pulmonary circulation. En: Copel JA, Reed KL, editores. Doppler ultrasound in Obstetrics and Gynecology. New York:Raven Press Edit; 1995.p.307-323.
10. Ortega R, Clarenbaux J, Pernetz MA, Rangosh A. Evaluación funcional del corazón fetal. Rev Obstet Ginecol Venez 1992;52(4):203-212.
11. Sosa A, García M, Guigni G. Evaluación de las ondas de velocidad de flujo Doppler de la arteria pulmonar fetal durante la gestación. Ultrasonido en Medicina 1998;14:1-5.
12. Achiron R, Heggesh J, Mashiach S, Lipitz S, Rotstein Z. Peripheral right pulmonary artery blood flow velocimetry: Doppler sonographic study of normal and abnormal fetuses. J Ultrasound Med 1998;17(11):687- 692.
13. Grannum P, Berkowitz RL, Hobbins J. The ultrasonic changes in the maturing placenta and their relation to fetal pulmonic maturity. Am J Obstet Gynecol 1979;133:915-918.
14. Zilianti M, Fernandez S. Correlation of ultrasonic images of fetal intestine with gestational age and fetal maturity. Obstet Gynecol 1983;62:569-561.
15. Gentili P, Trasimeni A, Giorlandino C. Fetal osification centers as predictors of gestational age in normal and abnormal pregnancies. J Ultrasound Med 1984;3:193- 196.
16. Goldstein P, Gershenson D, Hobbins J. Fetal biparietal diameter as a predictor of a mature lecithin/sphingomyelin ratio. Obstet Gynecol 1976;48:667-669.
17. Gross TL, Wolfson RN, Kuhnert PM. Sonographically detected free-floating particles in amniotic fluid predict a mature lecithin-sphingomyelin ratio. J Clin Ultrasound 1985;13:405-407.
18. Sosa A. Ultrasonografía y Clínica Embrio-Fetal Valencia, Venezuela: Editorial Tatum; 1993.

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