Year : 1999 | Volume
: 9 | Issue : 3 | Page : 119--125
Doppler velocimetry of uterine and umbilical arteries during pregnancy
Bhushan N Lakhkar, Shefeek A Ahamed
Department of Radiodiagnosis, Kasturba Medical College, Manipal-576119, Karnataka, India
Bhushan N Lakhkar
Department of Radiodiagnosis, Kasturba Medical College, Manipal-576119, Karnataka
To study the pulsatility index (PI), resistance index (RI) and systolic/diastolic (S/D) ratio of the «DQ»umbilical«DQ» and «DQ»uterine«DQ» arteries during pregnancy. To determine the normal range (mean + 2SD) for the various indices in our population. To also determine the statistical significance (P-value) of these values by comparing them with the abnormal indices in pregnancies that developed pregnancy-induced hypertension (PIH), and small for gestational age (SGA) babies. To determine which artery «DQ»umbilical vs. uterine«DQ» and which index PI vs. RI vs. S/D, serve as better indicators for bad maternal and perinatal outcome in PIH and SGA babies. To conclude whether a Doppler study can be an effective screening test.
Materials and Methods:
A total of 120 random pregnancies were screened at 20, 28 and 34 weeks of gestation. A color Doppler scanner with a carrier frequency of 3.5 MHz was used for studying the uterine and the umbilical arteries. Pregnancies with a normal outcome were used for calculating the normal range of various indices and for testing the specificity and negative predictive value (NPV) of the study. Those pregnancies with an abnormal outcome (PIH and SGA babies) were used for calculating the sensitivity and positive predictive value (PPV) of the study.
In normal pregnancies, the flow velocity waveforms (FVWs) showed a good diastolic flow and fall in indices as pregnancy progressed. A low diastolic flow and high indices characterized the pregnancies with abnormal outcomes. The uterine artery had a better sensitivity and specificity as compared to the umbilical artery. Among the various uterine waveform parameters, the diastolic notch had the highest sensitivity and specificity. Among the umbilical indices, the PI had the highest sensitivity and specificity.
Doppler provides a non-invasive method of assessing the fetal and maternal circulation during pregnancy. Both uterine and umbilical arteries have a low sensitivity at 20 weeks and therefore cannot be used as a screening test.
|How to cite this article:|
Lakhkar BN, Ahamed SA. Doppler velocimetry of uterine and umbilical arteries during pregnancy.Indian J Radiol Imaging 1999;9:119-125
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Lakhkar BN, Ahamed SA. Doppler velocimetry of uterine and umbilical arteries during pregnancy. Indian J Radiol Imaging [serial online] 1999 [cited 2020 Feb 22 ];9:119-125
Available from: http://www.ijri.org/text.asp?1999/9/3/119/28317
Pregnancy-induced hypertension (PIH) and small for gestational age (SGA)babies are both pathological conditions, which are strongly related to placental development and function. They are conditions related to improper flow of blood through the uterine and umbilical arteries.
During normal pregnancy, physiological modifications of the utero-placental and umbilico-placental bed take place to permit a decrease in vascular resistance and consequent increase in diastolic flow. Failure of this physiological process results in increased vascular resistance and fall in diastolic flow resulting in abnormal pathological conditions.
Doppler US provides a means of studying these circulatory beds and detecting abnormal vascular resistance patterns in the uterine and umbilical arteries non-invasively.
The purpose of this study was to evaluate the uterine and umbilical arteries at 20, 28 and 34 weeks of gestation using Doppler techniques. The study included various indices such as pulsatility index (PI), resistance index (RI) and systolic/diastolic (S/D) ratio and their usefulness as screening tests.
Materials and Methods
A total of 120 random patients over a period of one year were screened with successive Doppler scans at 20, 28 and 34 weeks of gestation. A color Doppler scanner (Ultramark-9, ATL) with a carrier frequency of 3.5 MHz was used.
The uterine artery was studied by first identifying the placental site. If the placenta was unilateral, the uterine artery of that side was studied. If the placenta was central, both uterine arteries were studied. The uterine signal was obtained per abdomen by pointing the probe in the iliac fossa towards the lower paracervical area. In the color mode, the uterine artery is seen to cross the external iliac artery, just after its origin from the internal iliac artery and this point was taken as the sampling point [Figure 1]. The umbilical artery was identified within the amniotic fluid by the appearance of parallel line echoes, which displayed a pulsatile activity on real-time images. The recording was taken close to the placental site of the umbilical cord [Figure 2].
The flow velocity waveforms (FVWs) obtained from both the umbilical and uterine arteries were computed automatically. The program identified individual cardiac cycles and computed peak systolic velocity, end diastolic velocity, mean velocity and the indices RI, PI and S/D [Figure 3]. Three such FVWs were obtained for each artery and the average value was recorded.
A patient was diagnosed to have PIH if there was a rise in systolic pressure of at least 30 mm of Hg or a rise in diastolic pressure of at least 15 mm of Hg over the previously known blood pressure. If the previous blood pressure was not known, an absolute rise in the blood pressure of at least 140/90 mm of Hg was taken to mean that the patient suffered from PIH. SGA babies were those with weights below the tenth percentile of the average weight for gestational age.
Seventy-one patients with a normal outcome were used for calculating the normal mean and standard deviation values. [Table 1] shows the mean and standard deviation of normal uterine artery indices RI, PI and S/D at 20, 28 and 34 weeks of gestation.
A line graph representation of various normal uterine artery indices at 20, 28 and 34 weeks of gestation is shown [Figure 4], where the top line with triangular insets represents the upper limit of normal i.e, mean +2SD. [Table 2] shows the mean and standard deviation values of the normal umbilical artery indices at various periods of gestation. A line graph representation of various normal umbilical artery indices at 20, 28 and 34 weeks of gestation is shown [Figure 5], where the top line represents mean +2SD values.
[Table 3] shows that there was a statistically significant difference in values between the normal uterine artery and abnormal uterine artery values, i.e, pUterine Artery
The main branch of each uterine artery enters the uterus just above the cervix and ascends along the lateral part of its wall. These peripheral branches give rise to arcuate arteries that derive their name from the arching pattern in the uterus. The arcuate arteries give off multiple branches of penetrating vessels called radial arteries. As the radial arteries approach the uterine cavity they become spiral arteries [Figure 6]. In the non-pregnant state, the uterine artery is a high resistance vessel. In normal pregnancy, trophoblasts invade the spiral arteries, stripping their musculoelastic coat and converting them into low resistance vessels [Figure 7].
In normal outcome pregnancies, there is an increase in the diastolic flow and consequent fall in indices [Figure 8]. In abnormal pregnancies (PIH and SGA babies) there is lack of trophoblastic invasion, as a result of which the uterine artery maintains its non-pregnant flow status. The velocity waveforms are characterized by a low diastolic flow, diastolic notch, biphasic deceleration slope and elevated indices [Figure 9],[Figure 10].
The presence of a diastolic notch is a normal phenomenon up to 26 weeks of gestation. Presence of a notch after 26 weeks is a bad indicator leading to hypertensive and SGA complications . Persistence of a notch after 26 weeks indicates vasospasm.
In normal pregnancy, as placental growth continues there is an overall increase in the number of tertiary stem villi and total number of small arterial channels (resistance vessels) [Figure 11]. This causes a normal drop in vascular resistance in the umbilical artery. In cases of umbilical placental insufficiency, there is a decrease in the resistance vessel count thereby leading to high resistance in the umbilical artery.
As gestation progresses, a low resistance in the umbilical artery is seen as good diastolic flow and fall in indices [Figure 12]. High resistance in the umbilical artery is characterized by a fall in diastolic flow and an absence/reversal of diastolic flow [Figure 13],[Figure 14],[Figure 15].
In our study, the normal outcome pregnancies without SGA babies and PIH, showed an increase in diastolic flow and fall in indices in the uterine and the umbilical arteries. The same observation was noted by Trudinger
et al .
In the abnormal outcome pregnancies, the uterine and umbilical arteries had a reduced diastolic flow or even absent/reversed diastolic flow. The same observations were noted by Campbell  and Schulman .
Comparing both the arteries, it was seen that the uterine artery had a better specificity, sensitivity, NPV and PPV as compared to the umbilical artery. Among the uterine parameters the diastolic notch and PI showed the highest sensitivity, specificity, NPV and PPV values. Sarah et al in their study also found the specificity of the diastolic notch to be the highest .
Among the umbilical parameters, the PI had the highest sensitivity, specificity, NPV and PPV. Absence or reversal of diastolic flow in the umbilical artery had the gravest outcome, as shown by Mc Parland .
At 20 weeks interval, the chances of either the umbilical artery or the uterine artery Doppler showing true positive cases are less and therefore Doppler velocimetry cannot be used as a screening test.
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