Guidelines and Recommendations on the use of Ultrasound in Obstetrics and Gynecology Article Swipe

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Alexandra Matias , Nuno Montenegro · YOU? · · 2015 · Open Access · · DOI: https://doi.org/10.5005/dsjuog-9-2-203

DSJUOG DSJUOG Guidelines and Recommendations on the use of Ultrasound in Obstetrics and GynecologyDuctus venosus (DV) is the main distributor of placental blood and directs well oxygenated blood from the umbilical vein to the cerebral and coronary circulations, across the foramen ovale toward the left atrium 1,5 (Fig. 1).This Y-shaped jet is arranged spatially in two pathways: Via sinistra (dorsal and left side stream): Thirty percent (at mid-gestation) and 20% (at term) of umbilical blood is accelerated to the left atrium through the foramen ovale shunted from the DV and left hepatic veins.Via dextra (ventral and rightward stream): Seventy percent of less oxygenated blood enters the right ventricle through the tricuspid valve, originating from the inferior vena cava.The DV is located in the fetal abdomen, connecting the intra-abdominal ventral portion of umbilical sinus to the left side of the inferior vena cava, and streams caudocranially and ventrodorsally.Due to this architectural arrangement (sphincter-like), a pressure gradient is produced between the umbilical vein and the atrium, resulting in the acceleration of the blood flow in the DV and producing a triphasic high velocity waveform. 1 A characteristic anterograde triphasic waveform is produced with a S-wave (ventricular systole), a D-wave (early diastole) and a A-wave (late diastole) evaluated by pulsed Doppler (Fig. 2).This latter wave presents the lowest velocity but always with forward flow.The peak velocity attained in the A-wave is about 3 to 4 times the velocity in the umbilical vein. 4 Unlike the second and third trimester, where the flow during the atrial contraction is always forward in normal pregnancies, one must take in consideration that in the early 1st trimester the A-wave can be null or reversed even in normal fetuses.However, after 11 weeks the presence of a reversed A-wave is considered abnormal (Fig. 3).Therefore, an easy qualitative assessment can be performed in routine clinical practice classifying the A-wave as positive, absent or reversed. 3 However, in order to quantify blood flow in the DV, several authors have suggested different indexes, such as pulsatility index for veins (PIV), S/D index, the ductus venosus index (DVI) defined as (S-a)/S or (S-a)/D, and the perfusion index (PFI) defined as Tamx/S. 6Strict methodological principles should be adopted in order to obtain a reproducible and clinically relevant waveform (Table 1).There is obviously a learning curve that implies the performance of 100 scans.The Doppler evaluation of DV is based on a right parasagittal plane obtained by B-mode, taking care to avoid contamination by neighboring vessels (hepatic veins, inferior vena cava and umbilical vein) (Fig. 4).The identification of the DV is greatly aided by using color Doppler putting the gate directly on the aliasing zone.The DV is distinguishable from the UV by a distinctly higher velocity.

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Guidelines and Recommendations on the use of Ultrasound in Obstetrics and Gynecology

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Alexandra Matias, Nuno Montenegro

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Obstetrics and gynaecology, Obstetrics, Medicine, Gynecology, Medical physics, Pregnancy, Biology, Genetics

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