COLOR DOPPLER IMAGING OF

UTEROPLACENTAL CIRCULATION

NORMAL PATTERN

During the first 12-13 weeks of a normal gestation, the uteroplacental and fetoplacental circulations are not in direct contact with each other (1,2). There is no active blood flow through the decidual spiral arteries into the intervillous space (3).

ABNORMAL PATTERN

High resistance to blood flow within the decidual spiral arteries and the presence of arterial blood in the intervillous space is associated with a high risk of early miscarriage (4). This is thought to be due to abnormally high-pressure flow on the immature placenta resulting in disengagement of the early villi, and subsequent miscarriage.

Endovascular trophoblast invasion has been considered to serve the "purpose" of establishing, from the earliest days of gestation, a maternal circulation providing the conceptus with nutrients. This circulation was conceived originally as a sluggish capillary derived blood pool, which evolves with trophoblast remodeling of the spiral arteries into a high-volume, low-resistance circuit.

Hustin and Schaaps have challenged this theory based on their failure to identify intervillous circulation both on direct visualization of the intervillous space and in perfused hysterectomy specimens. They demonstrated occlusion of the uteroplacental circulation by trophoblastic plugs until the twelfth week of pregnancy. They speculated that these trophoblastic plugs protect the young conceptus from the force of maternal arterial blood flow until implantation is well-established. Since then, it has been proposed that precocious initiation of maternal arterial perfusion of the intervillous space may be responsible for early pregnancy loss. The issue of whether the entire period of embryogenesis occurs without any direct contact with the maternal circulation has not been resolved. A cogent rebuttal has suggested that fixation artifact and intervillous flow rates (below the current limits of Doppler resolution) may explain most of the observations. The issue of whether most or all of embryogenesis occurs in the absence of contact with the maternal circulation awaits final resolution.

REFERENCES

1. Hustin J Schaaps JP. Echocardiographic and anatomic studies of the maternotrophoblastic border during the first trimester of pregnancy. Am J Obstet Gynecol 1987,157:162-168.
2. Janiaux E, Burton GJ, Muscoso GJ, Hustin J. Development of the early human placenta: a morphometric study. Placenta 1991,12:269-276.
3. Jaffee R, Woods JR. Color doppler imaging and in vivo assessment of the anatomy and physiology of the early uteroplacental circulation. Fertil Steril 1993,60:293-297.
4. Jaffee R, Dorgan A, Abramowicz JS. Color doppler imaging of the uteroplacental circulation in the first trimester. AJR 1995,164:1255-1258.