Fetal Circulation

Published on 07/06/2015 by admin

Filed under Neonatal - Perinatal Medicine

Last modified 07/06/2015

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1 Fetal Circulation

II. OVERVIEW OF THE FETAL CIRCULATION

Fetal circulation is shown in Figure 1-1.

image

Fig. 1-1 The fetal circulation. Ao, aorta; DA, ductus arteriosus; DV, ductus venosus; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.

(From Rudolph A: Congenital Diseases of the Heart: Clinical-Physiological Considerations, 2nd ed. Armonk, NY, Futura, 2001. Used with permission.)

III. THE PLACENTA

B. Function

1. The placenta provides nutrients and respiratory gas and metabolic exchange between the mother and fetus.

2. Uteroplacental flow increases during gestation in three phases as a result of vasodilation.

a. The first phase may occur within days or weeks of pregnancy.

b. The second phase occurs with development of intravillous spaces.

c. The third phase occurs during rapid fetal growth after 30 weeks. This corresponds with a change in uterine blood flow from less than 1% of the maternal cardiac output to 16% to 25% near term.

3. Fetoplacental circulation.

a. Complete fetoplacental circulation is established around the start of the fifth week after conception.

b. Fetoplacental blood flow, like uteroplacental flow, exponentially increases throughout gestation.

c. Placental blood volume is approximately 30% of the combined fetal cardiac output between 20 weeks and term.

4. Umbilical flow (Fig. 1-2).

a. In the first trimester, umbilical artery Doppler flow studies have demonstrated a gestational-age-dependent fall in placental resistance, with essentially no forward diastolic flow in the late first trimester.

b. In the second and third trimesters, Doppler flow studies indicate increasing flow velocities in diastole in keeping with the decreasing placental resistance.

IV. FETAL SHUNTS

Three shunts are present in the fetus and are critical in directing blood flow and in permitting the parallel circulation.

A. Ductus venosus (Fig. 1-3)

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