Umbilical Cord and Placenta

and Marcelo Zugaib4



(1)
São Paulo University, Bauru, Brazil

(2)
Parisian University, Bauru, France

(3)
Member of International Fetal Medicine and Surgery Society, Bauru, Brazil

(4)
Obstetrics, University of São Paulo, Bauru, Brazil

 



The assessment of the umbilical cord can be made from the early stages of pregnancy, still in the embryonic period, but a better definition of its components is achieved after 10 weeks’ gestation.

Usually the umbilical cord contains three vessels, two arteries and one vein, this last coming from physiological involution from one of the umbilical veins (the right one) at the beginning of the embryo formation. These vessels are covered by variable amounts of a gelatinous material made mostly of collagen, which is called Wharton’s jelly.

The umbilical cord has variable lengths, and is considered normal if it measures 30–120 cm in the third trimester of pregnancy. Its average length is 55 cm. Cord insertion in the placenta is normally central, but it could occasionally be peripheral and more rarely velamentous.

The normal aspect of the cord can be viewed through cross or longitudinal ultrasound sections, in which the two arteries and the single vein can be easily identified, displayed in a helical arrangement.

The presence of two umbilical arteries can be confirmed through a transverse view of the fetal pelvis, where they can be observed in their intra-abdominal portion, surrounding the bladder. In this spot, individualization of the arteries becomes easier using the color Doppler tool.

The cord abnormality most frequently encountered is the single umbilical artery, present in about 0.8% of single pregnancies, 5% of twin pregnancies, and 2.5% of abortions. It constitutes a warning to investigate the fetus in detail for other malformations and it is also imperative to carry out an echocardiogram. In this situation, the absent artery was formed in the early stages of the embryonic period, and deteriorated following atrophy.

The identification of the single umbilical artery is usually simple using the ultrasound sections previously mentioned for the assessment of the umbilical cord. Umbilical cords with an excessive number of vessels, the opposite situation, can also occur, although it is very rare. The umbilical cord may also harbor solid and cystic tumors.

Cystic images may correspond to allantoid cysts, omphalomesenteric duct, or amniotic inclusion. In particular, they should be distinguished from varicose dilation of the cord, which has a detectable flow on color Doppler.

The solid images, in turn, may correspond to the focal thickening of Wharton’s jelly, hematomas (usually post-puncture) or neoplasms such as hemangiomas and teratomas. They should mainly be distinguished from true and false umbilical cord knots.

The placenta, which is usually left to be assessed during the last few minutes of the obstetric examination, should not receive less attention and can equally present pathological conditions that could be diagnosed in utero.

Besides its location and degree of maturity (mentioned in Chap. 1), a detailed investigation should be made in a search for abnormalities.

Placentas may present abnormalities resulting from the implantation process, changes in its consistency or thickness, and the development of tumors.

As for the abnormalities resulting from the implantation process, the following can be seen using obstetric ultrasound examination: placenta with an accessory segment (placenta succenturiata), placenta previa (covering the cervical internal os at the beginning of labor), placenta accreta, placenta percreta, placenta increta, and chorioamniotic crossbeams.

The conditions that demand more experience and skill from the sonographers are placentas accreta, percreta, and increta. These may show subtle changes such as light interruption of the boundary separating the placenta from the myometrium, but also very gross and obvious changes such as bladder mucosa involvement.

The chorioamniotic band are not important when independent from fetal parts, as they are identified as hyperechoic cords amid amniotic fluid, which usually extends from the placental mass to the amnion and chorion nearby.

Placental thickness is commonly seen in specific conditions such as hydrops, fetal infections, and gestational diabetes.

Another diffuse alteration is characterized by the presence of hypoechoic images dispersed in a placental mass with consistency similar to gelatin, denominated jelly-like placenta and not showing pathological significance in most cases.

Placental neoplasms may belong to the group of gestational trophoblastic disease or be isolated tumor masses represented mostly by hemangiomas and teratomas.

Gestational trophoblastic disease is addressed in Chap. 2 on early pregnancy.

Hemangiomas and teratomas may present as solid masses with variable heterogeneity and echogenicity; hemangiomas are usually more common.

Ultrasound can also be effectively used for the detection of detachment areas, both in the early stages of pregnancy and in advanced stages.

In the detachment area, the blood collection can usually be identified. It appears as an anechoic or hypoechoic area in cases of more recent bleeding or occasionally it may appear as heterogeneous or hypoechoic areas in cases of older hematomas or organized hematomas. It should be remembered, however, that the overall sensitivity of the ultrasound for placental abruption does not exceed 70%.

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Fig. 14.1
Cross-section at the level of the insertion of the normal umbilical cord (white arrow) in the fetal abdomen. Notice the two umbilical arteries (black arrows) surrounding the bladder (B). A = free cord loop, O = iliac bones


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Fig. 14.2
Same section as that shown in Fig. 14.1 showing the detection of flow in the two umbilical arteries using color Doppler. The visualization of the umbilical arteries (arrows) makes it easy to see and in some situations even define the image of the bladder


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Fig. 14.3
Cross-section of the umbilical cord showing two arteries (A) and one vein (V), which together form a typical image denominated “Mickey’s head”

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Dec 28, 2017 | Posted by in GYNECOLOGY | Comments Off on Umbilical Cord and Placenta
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