European Journal of Cardiovascular Medicine

The placenta is an organ which provides the physiologic link between a pregnant female and her fetus [1]. The human placenta is concerned with exchanges that occur between maternal and fetal bodies. It originates from two basic components: (i) Fetal portion – chorion frondosum and (ii) Maternal portion – Endometrium, more specifically from decidua basalis [2]. The placenta develops from the chorionic villi at the implantation site at about the fifth week of gestation and by the ninth or tenth week, the diffuse granular echo texture of the placenta is clearly apparent at sonography [1].

At term, the placenta is discoid with a diameter of 15 to 25 cm and is approximately 3 cm thick and weighs about 500-600 grams. Fetal growth parameters, especially BPD (Biparietal diameter) and AC (Abdominal Circumference) are adversely affected by insufficient nutrients reaching the fetuses through the placenta. In these type of growth retarded fetuses, placenta is often thin [3].

Studies have shown that diminished placental size precedes fetal growth retardation as intrauterine growth restriction (IUGR) is associated with impoverished villous development and fetoplacental angiogenesis [1]. A very small placenta is associated with growth restriction. Also, an excessively large placenta may be associated with infection, anemia or Triploidy [2].

Thus, Placental thickness appears to be a promising parameter for estimation of gestational age of the fetus because of increase in placental thickness with gestational age. Subnormal placental thickness can be an early indicator of IUGR [4] [5]

The umbilical artery is the most extensively investigated vessel in the assessment of fetal well-being by Doppler velocimetry and waveform. Abnormal Doppler waveform indices of the umbilical artery have been demonstrated to be a measure of increased resistance in the umbilical-placental circulation. The pathologic basis for this phenomenon appears to be a decrease in the number of tertiary villous arteries and arterioles and is observed in the setting of preeclampsia, IUGR and fetal chromosome anomalies.

Since the primary site of vascular abnormality is further downstream in the tertiary villi of the placenta, alterations in umbilical artery Doppler waveforms merely reflect the distal vascular abnormality and occur relatively late in the process. It would be therefore desirable to examine the intraplacental villous vasculature by Doppler velocimetry and waveform directly, as opposed to examining the upstream umbilical artery and it may be an early predictor of IUGR [6].

It is thus clear that normal development of placenta during gestation is necessary for supporting healthy fetus. On the other hand, any impairment in its development may have profound impact on fetal development and pregnancy outcome.

The current study discusses the importance of placental thickness and intraplacental Doppler in normal and growth retarded fetuses.

This prospective study was conducted over a period of one year and five months from July 2019 to November 2020, aiming to investigate the relationship between gestational age and antenatal ultrasound findings in singleton pregnant females. The study enrolled 118 out of 124 pregnant females who visited Radiology Department for routine antenatal scans, with six excluded due to non-attendance at follow-up appointments.

The inclusion criteria consisted of a singleton pregnancy, known last menstrual period date, and gestational age between 16 to 20 weeks. Exclusion criteria included twins, congenital malformations, gestational hypertension, diabetes mellitus, hydrops fetalis, irregular menstrual cycles, severe anaemia, polyhydromniosis, abnormal placentation, placenta with variations in insertion of the umbilical cord, and certain conditions such as polyhydramnios.

The fetal biometric parameters, including BPD, HC, AC, and FL, were measured using a digital ultrasound device to assess the growth and development of the fetus throughout its gestational period. The placental thickness at the site of insertion of the umbilical cord was also evaluated, as well as the PI (placental implantation site) RI (recumbent insertional ratio) and S/D (stretch/density ratio) values of the intraplacental villous vessels, which are indicators of fetal well-being. The ultrasonic probes used were C6-2 with a frequency of 2-6 MHz to provide clear images of the fetus's anatomy.

All the antenatal females satisfying the inclusion and exclusion criteria as mentioned above, were enrolled in the study after taking an informed consent. A brief history of the patient was taken and then the following ultrasonographic parameters were noted by a single radiologist.

1. Site of insertion of placenta
2. Placental thickness at site of insertion of umbilical cord
3. Fetal biometric parameters BPD, HC, AC and FL
4. PI, RI and S/D values of intraplacental villous vessels
5. PI, RI and S/D values of umbilical artery

The evaluation was done using a curvilinear C6-2 (2-6 MHz) on a PHILIPS AFFINITI 50G USG machine in the Department. of Radiology.

The patients were followed up and were labelled as appropriate for gestational age or IUGR

The foetuses with estimated fetal weight less than 10^th percentile of normal for that particular gestational age based on Hadlock’s chart were considered IUGR.

The study was conducted on Philips Affiniti 50 G ultrasound machine using probes of appropriate frequency.

The F forms were filled as per PC-PNDT rules and duly submitted every month.

Sonographic technique of measuring placental thickness:

The patient was scanned in supine position. The transducer was placed on the skin surface after applying the couple agent. The placental thickness in cm was measured at the level of cord insertion site. The transducer was oriented to scan perpendicular to both the chorionic and basal plates as tangential scan will distort the measurement of the thickness of the placenta. The identification of the cord insertion site is vitally important for obtaining correct measurements. The site is usually central but slightly eccentric position may be normal. The ultrasonic appearance of the cord insertion appears either as hypoechoic areas closest to the chorionic plate in the thickest portion of the placenta with a v shape or as linear echoes emanating at right angles from the placental surface. Placental thickness was calculated from the echogenic chorionic plate to placental myometrial interface near the mid-placental portion. The myometrium and subplacental veins was excluded in the measurements. All placental measurements were taken during the relaxed phase of the uterus as contractions can spuriously increase the placental thickness. The thickness increases during contraction due to distension of intervillous spaces by maternal blood. The length and surface of placenta can also increase due to distention of intervillous space. Placental thickness depends on amount of fetal blood, maternal blood and placental tissue. Correct identification of placental myometrial interface is important for proper measurements of placenta. Placental thickness value, in cm, was calculated by averaging the three best measurements for each case.

Fig 1: shows placental thickness measured at the site of insertion of umbilical cord.

Technique of intraplacental doppler:

After routine fetal biometry, color and power Doppler images were obtained to detect the intraplacental villous vessels. The location of the placenta was identified in the abdominal surface. Then, the placenta was continuously scanned from one side to the other side. The entire placenta was scanned, keeping the angle of the ultrasonic probe perpendicular to the uterine wall.

Careful attention was paid to optimizing Doppler settings for each individual patient. Instead of fixed function control settings, Doppler gain and flow velocity settings were adjusted until maximal color Doppler signals were obtained, without producing diffuse color artifacts. After localization of blood flow with color Doppler, a spectral Doppler display was obtained by superimposing the Doppler gate over the area of color flow on the screen and PI, RI and S/D values were noted.

Fig 2: shows Colour and Spectral Doppler pattern of intraplacental circulation

Technique of umbilical artery doppler:

Ideally, the fetus should be at rest and not breathing, because movement and breathing cause variations in the spectral waveform. The angle of insonation is not crucial, because all of the measurements used clinically are ratios, but an angle close to 0° results in the best Doppler shift and waveforms. The cord is visualized and a free loop is selected not too close to the fetal cord insertion or the placental insertion. It is then zoomed up if necessary and then colour Doppler is switched on and optimized followed by use of spectral Doppler to obtain a spectral trace and PI, RI and S/D values are obtained.

Fig 3: show color Doppler ultrasound image at the free loop of the umbilical cord depicting a normal spectral waveform with continuous flow throughout the cardiac cycle

The study utilized a proforma to assess the correlation between placental thickness, color Doppler flow patterns, and flow velocity waveforms of intra-placental fetal circulation in normal and growth-retarded foetuses. Data collection included personal biodata such as name, age, sex, contact information, admission and discharge dates, and ward/unit details. A brief history was obtained, encompassing chief complaints, past medical history, family history, menstrual history, and obstetric history.

The results were analyzed through data entry in Excel, focusing on the relationship between placental 

Table 1: Incidence Of Iugr

According to our study, the incidence of IUGR during the study period at Baroda Medical College and S.S.G. Hospital was 12.6%.

Table 2: Distribution Of The Pregnant Females In Terms Of Age (Years)

Table 3: Parity Distribution In Antenatal Females With Normal Pregnancy Outcome

Out of 103 antenatal females with normal pregnancy outcome, 49 were primigravida, the incidence being 47.57 %, 28(27.18%) were second gravida, 17(16.5%) third gravida, 8 (7.76%) were 4^th gravida and 1(0.97%) 5^th    gravida.

Table 4: Parity Distribution In Antenatal Females With Iugr Foetuses

Out of 15 antenatal females with IUGR, 3 were primigravida, the incidence being 20 %, 2(13.33%) were second gravida, 6(40%) third gravida and 4 (26.66%) were 4^th gravida.

Table 5: Site Of Placenta

Table 6: Gestational Age At The Time Of Delivery

Table 7: Birth Weight At The Time Of Delivery

Table 8: Mean Placental Thickness In Normal Uncomplicated Pregnancies

There is a significant increase in placental thickness noted at consecutive scans as gestational age advances in normal, uncomplicated pregnancies (p < 0.001).

Table 9: Mean Placental Thickness In Iugr Fetuses

There is a significant increase in placental thickness noted at consecutive scans as gestational age advances in IUGR pregnancies (p < 0.001).

Table 10: Percentage Increase In Mean Placental Thickness In Normal And Iugr Pregnancies With Advancing Gestational Age

Fig 4: Line Chart showing increase in placental thickness with in normal and IUGR pregnancies with advancing gestational age.

Placental thickness was observed to be lower in IUGR pregnancies as compared to normal uncomplicated pregnancies at all the visits. (p < 0.05)

Table 11: Mean Intraplacental Doppler Indices In Normal Pregnancies

As the gestational age advances; PI, RI and S/D values of IPVA Doppler consistently decrease at each visit in normal uncomplicated pregnancies. (p < 0.001)

Table 12: Percentage Decrement Of Doppler Indices On Follow Up Visits

Fig 5: Line Chart depicting decrease in IPVA PI, RI and S/D values with advancing gestational age in normal pregnancies.

Table 13: Mean Intraplacental Doppler Indices In Iugr Pregnancies

As the gestational age advances; there is a significant decrease in PI, RI and S/D values of IPVA Doppler between 2^nd and 3^rd visits in IUGR pregnancies. (p < 0.05)

There is no significant difference in PI, RI and S/D values of IPVA Doppler between 1^st and 2^nd as well as 3^rd and 4^th visits

Table 14: Percentage Decrement Of Doppler Indices On Follow Up Visits

Fig 6: Line Chart depicting decrease in IPVA PI, RI and S/D values with advancing gestational age in IUGR pregnancies

The mean PI, RI and S/D at consecutive weeks are higher in IUGR pregnancies as compared to normal uncomplicated pregnancies.

Table 15: Mean Umbilical Artery Doppler Indices In Normal Pregnancies

As the gestational age advances; PI, RI and S/D values of Umbilical artery Doppler consistently decrease at each visit in normal uncomplicated pregnancies. (p < 0.001)

Table 16: Percentage Decrement Of Umbilical Artery Doppler Indices On Follow Up Visits In Normal Pregnancies

Fig 7: Line Chart depicting decrease in UA PI, RI and S/D values with advancing gestational age in normal uncomplicated pregnancies.

Table 17: Mean Umbilical Artery Doppler Indices In Iugr Pregnancies

As the gestational age advances; there is a significant decrease in PI and S/D values of UA Doppler between 1^nd and 2nd visits in IUGR pregnancies. (p < 0.05). Also, there is a significant decrease in S/D values between 2^nd and 3^rd visits. (P < 0.05)

Table 18: Percentage Decrement Of Umbilical Artery Doppler Indices On Follow Up Visits In Iugr Pregnancies

Fig 8: Line Chart depicting decrease in UA PI, RI and S/D values with advancing gestational age in IUGR pregnancies

The mean PI, RI and S/D at consecutive weeks are higher in IUGR pregnancies as compared to normal uncomplicated pregnancies.

There is a significant difference in PI, RI and S/D values of IPVA Doppler between pregnancies with normal outcome and IUGR pregnancies at all the 4 visits.

There is a significant difference in PI, RI and S/D values of UA Doppler between pregnancies with normal outcome and IUGR pregnancies at 2^nd, 3^rd and 4^th visits.

There is no significant difference in PI, RI and S/D values of UA Doppler between pregnancies with normal outcome and IUGR pregnancies as early as 16 to 20 weeks.

In this prospective study, 118 antenatal females were studied and followed up.

In our study, placental thickness increases with advancing gestational age in normal uncomplicated pregnancies. A fairly linear increase in mean placental thickness with gestational age was observed in correlation analysis studies conducted to determine the relationship between placental thickness and gestational age [3]. The value of the mean placental thickness increased with advancing gestational age, almost matching from 22^nd to 35^th week in a study conducted in India [7]. The importance of increase in placental thickness with advancing gestational age lies in the fact that lack of increase in placental thickness with advancing gestational age or a subnormal placental thickness with advancing gestational age may be an early indicator of IUGR. In our study, pregnancies with IUGR had lower mean placental thickness as compared to that of normal uncomplicated pregnancies at all visits.

Intra-placental and umbilical artery Doppler indices i.e. PI, RI and S/D were comprehensively examined in all the enrolled antenatal females. Mean PI, RI and S/D values of intra-placental circulation decrease with advancing gestational age in normal uncomplicated pregnancies. Thus, it confirms earlier reports that PI and RI indices of IPVA vessels gradually decrease with advancing gestation allowing for increase in uteroplacental flow. Fetal intra-placental arterial circulation consists of arteries in main, secondary and tertiary villi. The number of generation of vessels increase throughout pregnancy and total vascular cross section area increases with each additional gestation. Due to constant multiplication of tertiary villi, there is a progressive decrease in resistance to blood flow in the intra-placental arterial circulation as well as in the umbilical arteries.  Normal pregnancies hence demonstrate progressive reduction in placental resistance.

Intra-placental mean PI, RI and S/D values were higher in IUGR pregnancies as compared to normal uncomplicated pregnancies. The same was observed with umbilical artery Doppler indices. However, the mean PI, RI and S/D values of umbilical artery Doppler did not differ between normal uncomplicated pregnancies and pregnancies with IUGR as early as 16 to 20 weeks. Failure of proper development of secondary or tertiary villi leads to impaired uteroplacental circulation. This culminates in inadequate uteroplacental blood flow, hypoxia and oxidative stress which ultimately may lead to development of IUGR. This explains raised PI, RI and S/D ratio of IPVA Doppler in IUGR pregnancies as compared to normal uncomplicated pregnancies. Hence, they can be used for early diagnosis of IUGR [8].

However, from a clinical viewpoint, there is a dearth of literature examining IPVA-resistant indices and their possible relationship to placental mediated diseases like IUGR. Jaffe and Woods evaluated [9] a group of high-risk patients with abnormal first trimester Doppler characteristics, IPVA RI/UA RI ratios in the second trimester and showed an increased rate of pregnancy complications when the ratio was >1. However, two other studies did not demonstrate any benefits in screening and early identification of PMDs when examining IPVA Doppler’s. Romentsch et al, [6] in a cross-sectional study, failed to demonstrate a relationship between predicted and observed cases of IUGR by measuring IPVA Doppler. Moreover, they were unable to detect intra-placental blood flow in 28% (8/29) of patients with IUGR neonates, whereas in this study, IPVA Dopplers in all the cases were sampled.

This study showed similar result as compared to Babic et al, [10] a prospective study evaluating IPVA resistance indices in normal pregnancies and pregnancies with placental mediated diseases (i.e. pre-eclampsia and IUGR). They concluded that mean IPVA PI and RI are higher in antenatal females developing IUGR as compared to that in healthy pregnancies. The umbilical artery Doppler values did not differ between the groups as early as 18 to 20 weeks.

The study found that placental thickness increases with advancing gestational age in normal uncomplicated pregnancies, while placental thickness decreases in pregnancies complicated by intrauterine growth restriction (IUGR).

Additionally, Doppler ultrasound values for placental perfusion index (PI), resistance index (RI), and systolic/diastolic ratio (S/D) values from both IPVA and UA Doppler ultrasound decrease with advancing gestational age in normal uncomplicated pregnancies. However, in pregnancies complicated by intrauterine growth restriction (IUGR), these same Doppler indices are found to be higher than expected at earlier stages of pregnancy (16-20 weeks).

This suggests that these markers can be used to diagnose IUGR early in pregnancy, potentially allowing for earlier intervention and better outcomes.

1.      Mathai BM, Singla SC, Nittala PP, Chakravarti RJ, Toppo JN. Placental thickness: Its correlation with ultrasonographic gestational age in normal and intrauterine growth-retarded pregnancies in the late second and third trimester. J Obstet Gynecol India. 2013;63(4):230–3.

2.      Ahmed Abdalla Balla E. Prediction of Fetal Growth by Measuring the Placental Thickness Using Ultrasonography. J Gynecol Obstet. 2014;2(2):26.

3.      Ohagwu CC, Abu PO, Ezeokeke UO, Ugwu AC. Relationship between placental thickness and growth parameters in normal Nigerian foetuses. African J Biotechnol. 2009;8(2):133–8.

4.      Jauniaux E, Ramsay B, Campbell S. Ultrasonographic investigation of placental morphologic characteristics and size during the second trimester of pregnancy. Am J Obstet Gynecol. 1994;170(1 I):130–7.

5.      Mital P, Hooja N, Mehndiratta K. Placental thickness - A sonographic parameter for estimating gestational age of the fetus. Indian J Radiol Imaging. 2002;12(4):553–4 

6.      Rotmensch S, Liberati M, Luo J Sen, Kliman HJ, Gollin Y, Bellati U, et al. Color Doppler flow patterns and flow velocity waveforms of the intraplacental fetal circulation in growth-retarded fetuses. Am J Obstet Gynecol. 1994;171(5):1257–64.

7.      Mital P, Hooja N, Mehndiratta K. Placental thickness - A sonographic parameter for estimating gestational age of the fetus. Indian J Radiol Imaging. 2002;12(4):553–4.

8.      Bahtiyar MO, Copel JA. Cardiac Changes in the Intrauterine Growth-Restricted Fetus. Semin Perinatol. 2008;32(3):190–3. 

9.      Jaffe R, Woods JR. Doppler velocimetry of intraplacental fetal vessels in the second trimester: Improving the prediction of pregnancy complications in high-risk patients. Vol. 8, Ultrasound in Obstetrics and Gynecology. 1996. p. 262–6.

10.   Babic I, Ferraro ZM, Garbedian K, Oulette A, Ball CG, Moretti F, et al. Intraplacental villous artery resistance indices and identification of placenta-mediated diseases. J Perinatol. 2015;35(10):793–8.