14 Color Doppler Sonography of the Uterine Arteries in Early Pregnancy to Screen for Preeclampsia and Uteroplacental Insufficiency Placental insufficiency and preeclampsia in the third trimester. Doppler sonography of the uterofetoplacental unit in the third trimester is part of the standard diagnostic workup of patients with suspected placental insufficiency and preeclampsia. At this late stage of gestation, however, it is possible only to confirm the presence of a chronic perfusion deficit. The Doppler findings, along with B-mode findings and biophysical and biochemical tests, are helpful in assessing the degree of fetal compromise and directing clinical management. Early detection of decreased uterine perfusion. The efforts of modern medicine are also aimed at early detection, clinical intervention, and prevention, and these goals have prompted the use of transvaginal ultrasound scanning to assess blood flow early in the pregnancy. Changes in the spiral arteries. The central question is whether Doppler sonography is able to confirm the normal development of blood flow and also detect decreased blood flow during the first half of pregnancy. Another key issue is whether Doppler evidence of decreased uterine perfusion actually correlates with the development of pregnancy-induced hypertension (PIH) and intrauterine growth retardation. Normally a massive increase of blood flow occurs during the first half of pregnancy, and this requires a morphological transformation of the spiral arteries as described by Brosens et al.3. Trophoblastic cells invade and erode the musculoelastic media of the spiral arteries, transforming the vessels into large, saclike tubes with a funnel-like expansion at their junction with the intervillous space. These changes take place between the 14th and 20th weeks of menstrual age and are completed no later than the 24th week, even when maturation is delayed. The calibers of the spiral arteries are increased by a factor of 30, the arcuate arteries by a factor of 10, and the uterine arteries by a factor of 1.5–32. Blood circulation in the intervillous space. The blood flow changes that occur during the first trimester are more difficult to classify. Hustin and Shaaps7 performed hysteroscopic, radiological, and morphological studies showing that intervillous blood circulation does not occur before the 12th week of gestation. This led them to conclude that there is no contact between the chorionic villi and maternal blood during the first trimester and that the embryo and placenta are independent of the maternal environment. They distinguished between a period in which implantation, organogenesis, and placentation occur and a second period that begins with active maternal blood flow through the intervillous space toward the end of the first trimester. It is reasonable to conclude that uterine blood flow in the first trimester is controlled in part by the rising estrogen levels in the maternal serum. This can be inferred from the fact that cyclic changes in uterine blood flow correlate with the estradiol level4,12, that estrogen receptors have been identified in muscle cells of the uterine arteries9, and that animal studies have shown dilatation of the terminal segments of the uterine vessels prior to trophoblast invasion10. Transducer placement. With the patient in the lithotomy position, the ultrasound probe, sheathed in a condom and smeared with contact gel, is inserted into the vagina until it is in contact with the anterior fornix (anteflexed uterus) or posterior fornix (retroflexed uterus). An initial survey is carried out, and the probe is positioned in the lateral fornix so that it is in direct contact with the uterine attachment of the parametrium through the vaginal wall. The proximity to the target organs makes it possible to use transducer frequencies of 5 MHz or higher, which are excellent for blood flow studies. Vascular anatomy. After arising from the internal iliac artery, each uterine artery, surrounded by the uterine veins, curves over the ureter about 2 cm from the cervix and reaches the uterus at the level of the isthmus. There it divides into a descending cervical branch and an ascending branch. The latter branch ascends tortuously along the side of the uterus and anastomoses with the ovarian artery via the tubal branch. The best sites for recording Doppler signals are the main trunk of the uterine artery and the origin of the ascending branch. Both vessels can be clearly identified in those areas and can be scanned at an optimum beam–vessel angle. Advantages of transvaginal scanning. According to our studies, the transvaginal approach has several major advantages over transabdominal scanning, especially in early pregnancy examinations5: The Doppler spectra of the uterine arteries display characteristic changes from early pregnancy until the conclusion of trophoblastic invasion in midpregnancy (Fig. 14.1). Doppler spectra in early pregnancy. At the start of pregnancy, the Doppler spectra of the uterine arteries do not differ from those recorded in the periovulatory period. Highly variable patterns can occur. The spectra typically have a sharp systolic upstroke and downstroke with a sharp, narrow systolic peak and a low maximum frequency shift. A variable notch may appear in the systolic downstroke. The diastolic phase of the cardiac cycle consistently shows a very low frequency shift whose pattern changes more characteristically with advancing gestation than the systolic peak. During the first trimester the sharp systolic downslope typically ends in an early diastolic notch, which may convert to reverse flow during the initial weeks. The postsystolic notch is followed by a diastolic peak that shows the highest velocities in the diastolic part of the cardiac cycle during the first trimester. The end-diastolic frequency shift is low in the first trimester, and absent or reverse flow is seen in rare cases. These normal features during early pregnancy are useful for the visual interpretation of Doppler waveforms in cases where abnormalities develop later in the pregnancy.
Applications of Color Doppler Sonography during Pregnancy
Technique of Transvaginal Doppler Sonography
Accurate overall assessment of uterine perfusion
Greater pulsatility of blood flow, allowing better recognition of impedance criteria in the Doppler scan
Smaller range of error owing to a more favorable beam–vessel angle
Normal Development of Uterine Artery Doppler Spectra
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
