Fetal cardiac output and its distribution to the placenta and brain at 11-20 weeks of gestation

The three papers of the thesis are not available in Munin due to publisher's restrictions: 
<br>1. Vimpeli T, Huhtala H and Acharya G. 'Fetal echocardiography during routine first-trimester screening: a feasibility study in an unselected population' Prenatal Diagnosis 2006;26(5):475-482 (Wiley). Available at  <a href=http://dx.doi.org/10.1002/pd.1442>http://dx.doi.org/10.1002/pd.1442</a> <br>
2. Vimpeli T, Huhtala H, Wilsgaard T and Acharya G. 'Fetal cardiac output and its distribution to the placenta at 11-20 weeks of gestation' Ultrasound in Obstetrics and Gynecology 2009;33(3):265 - 271 (Wiley) <a href=http://dx.doi.org/10.1002/uog.6247>http://dx.doi.org/10.1002/uog.6247</a> <br>
3. Vimpeli T, Huhtala H, Wilsgaard T and Acharya G. 'Fetal aortic isthmus blood flow and the fraction of cardiac
output distributed to the upper body and brain at 11-20
weeks of gestation' Ultrasound in Obstetrics and Gynecology 2009;33(5):538-44 (Wiley) <a href=http://dx.doi.org/10.1002/uog.6354>http://dx.doi.org/10.1002/uog.6354</a>Objective: 
To study some aspects of fetal heart structure and function using ultrasonography at 11-20
weeks of gestation with an emphasis on the distribution of cardiac output to the placenta and
upper body including brain.
<br>
Methods:
In a cross-sectional study of unselected pregnant population, the structure of the fetal heart
was studied using transvaginal ultrasonography and feasibility of obtaining standard
echocardiographic views and measuring different structures was evaluated in 584 fetuses at
11+0-13+6 weeks of gestation. Reference ranges were established for the heart/ thorax
circumference ratio, ventricular size and the diameters of the aorta and main pulmonary artery
at the respective semilunar valve levels.
The fetal cardiac function was studied in a prospective longitudinal study of 143
pregnant women from an unselected population who were serially examined three times
during 11-20 weeks of gestation. Blood flow velocities and diameters of the main pulmonary
artery, aorta, aortic isthmus and umbilical vein were measured using pulsed-wave Doppler
and B-mode ultrasonography, respectively and the reference ranges were constructed. The
volume blood flow (Q) was calculated as a product of mean velocity and cross-sectional area
of the vessel. Reference intervals were established for the umbilical vein (Q<sub>uv</sub>) and aortic
isthmus (Q<sub>ai</sub>) volume blood flows and the left (LVCO), right (RVCO) and combined (CCO)
ventricular cardiac outputs. The fraction of CCO distributed to the placenta was calculated as:
Q<sub>uv</sub>/CCO*100 and the fraction of CCO distributed to the upper body and brain was calculated
as: (LVCO – Q<sub>ai</sub>)/CCO*100.
<br>
Results: 
It was possible to study the fetal heart anatomy by obtaining standard echocardiograhic views
using transvaginal ultrasonograpy in a majority of cases in the late first trimester. The cardiac
ventricles and their outflow tracts showed a linear growth with advancing gestational age
during 11-14 weeks of gestation.
The CCO increased 1.9-fold from 11 to 20 weeks of gestation and the placental
volume blood flow almost tripled during the same period. The fraction of CCO diverted to the
placenta increased from 14% at 11 weeks to 21% at 20 weeks.
Aortic isthmus had a positive forward flow during the whole cardiac cycle
during 11-20 weeks of gestation. Aortic isthmus blood flow velocities as well as the diameter increased with advancing gestation, resulting in a significant increase in Q<sub>ai</sub> from 1.9 to 40.5
ml/min during 11-20 weeks. However, the fraction of CCO directed to the upper body
including brain remained relatively stable (approximately 13%) during this gestational period.
<br>
Conclusion: 
It appears feasible to study fetal heart anatomy in late first trimester using transvaginal
echocardiography and to confirm normality. We have established references ranges for the
evaluation of some cardiac structures at 11-14 weeks of gestation and for the serial
measurement of Q<sub>uv</sub>, Q<sub>ai</sub> and cardiac ventricular outputs at 11-20 weeks of gestation. Placental
volume blood flow and the fraction of CCO distributed to the placenta increases substantially
during 11-20 weeks of gestation reflecting faster placental growth relative to fetal growth and
establishment of low resistance circulation during the first half of pregnancy. The fraction of
cardiac output directed to the upper body and brain is relatively small but fairly constant
during 11-20 weeks of gestation