|Year : 2015 | Volume
| Issue : 1 | Page : 4-8
Relationship between two-dimensional ultrasound measurement of placental thickness and estimated fetal weight
Ademola A Adeyekun, Joyce E Ikubor
Department of Radiology, University of Benin Teaching Hospital, PMB 1111, Benin City, Nigeria
|Date of Web Publication||26-Feb-2015|
Ademola A Adeyekun
Department of Radiology, University of Benin Teaching Hospital, PMB 1111, Benin City
Background/Aim: The placenta plays a major role in fetal well-being, and fetal weight is very important to neonatal survival. There probably exists a relationship between placental dimension and fetal size. Data on ultrasound assessed placenta thickness and fetal weight are scanty in the Nigerian literature. This study aimed to establish a relationship between ultrasound estimated placental thickness and fetal weight. Materials and Methods: Four hundred and twenty apparently healthy pregnant women at gestational age 15-40 weeks were sonographically examined, with a 3.5 MHz curvilinear transducer of a Sonoace X6 machine (Medison Co., Korea). Placenta thickness, in millimeters, and fetal weight, in grams, was estimated for each subject. Correlation between the two parameters was assessed. P ≤ 0.05 were considered to be significant. Results: Mean placental thickness (PT) ranged from 22.6 ± 2.5 mm at 15 weeks to 40.9 ± 7.2 mm at 30 weeks, while estimated fetal weight (EFW) ranged from 147.0 ± 16.5 g at 15 weeks to 3.304.8 ± 284.6 g at 40 weeks. The mean values of placenta thickness and EFW throughout gestation were 35.5 ± 7.0 mm and 1555.0 ± 1004 g, respectively. There was significant correlation between placenta thickness and EFW r = 0.668; P = 0.000. Conclusion: The study established a fairly linear relationship between placental thickness and EFW. A normogram of ultrasound estimated placenta thickness and fetal weight is derived.
Keywords: Fetal weight, Nigerian women, placenta thickness, ultrasound
|How to cite this article:|
Adeyekun AA, Ikubor JE. Relationship between two-dimensional ultrasound measurement of placental thickness and estimated fetal weight. Sahel Med J 2015;18:4-8
|How to cite this URL:|
Adeyekun AA, Ikubor JE. Relationship between two-dimensional ultrasound measurement of placental thickness and estimated fetal weight. Sahel Med J [serial online] 2015 [cited 2019 Jun 27];18:4-8. Available from: http://www.smjonline.org/text.asp?2015/18/1/4/152151
| Introduction|| |
Placental wellbeing and maternal health, in addition to genetically determined growth potential, are known factors that influence fetal growth. Indeed, placental disease has been shown to be the most clinically relevant of all potential underlying processes that may result in intrauterine growth restriction.  Fetal weight estimation is important because birth weight has been shown to be the single most important parameter that determines neonatal survival. 
Metzenbauer et al.  had reported an association between birth weight and sonographically estimated first trimester placental volume, while Thame et al.  showed that low-birth weight is often preceded by small placental size in the second trimester. In late pregnancy, placental dimensions have been shown to be independent, statistically significant variables associated with birth weight. 
Pathak et al.  examined the relationship between placental weight at birth and ultrasound estimated placental volume, and previous reports have linked small placental size with low-birth weight. ,, Two-dimensional ultrasonography has been proposed in estimating placental dimensions, since three-dimensional systems are time consuming and require expensive technology.  This is relevant for developing or low-level economies like Nigeria, especially where the high rate of pregnancy complications makes routine assessment of placental dimensions and fetal weight necessary. Placental examination may be the first demonstration of insufficiency of its function, as a precursor of fetal disorders, and increased placental size has been shown to be an independent predictor of fetal weight.  Thus the two variables, placenta size and fetal weight, can be compared in cases of high-risk pregnancies, especially when gestational age cannot be accurately determined. It is, therefore, relevant to prenatally assess any relationship between placental dimensions and ultrasound estimated fetal weight (EFW).
Although there are reports in the international medical literature on the association between placental dimensions and ultrasound EFW, such reports are scanty in the Nigerian environment.  This study, therefore, attempts to formulate a nomogram of ultrasound measured placental thickness and EFW according to gestational age. It is envisaged that early warning signs of intrauterine growth restriction may be apparent when placental thickness appears inappropriate at a corresponding gestational age, for EFW.
| Materials and methods|| |
Four hundred and twenty apparently healthy pregnant women referred for routine ultrasonography at the Department of Radiology, University of Benin Teaching Hospital, Benin City, Nigeria were prospectively recruited into the study. The approval of the Ethics and Research committee of the hospital was obtained. Only those women whose gestational ages, as established by fetal biometry, corroborated with their menstrual dates were included. Apart from unsure dates, other exclusion criteria were amniotic fluid abnormalities, rhesus isoimmunization, fetal anomalies, and uterine masses. Each subject was scanned once.
Scanning was done with a 3.5 MHz curvilinear transducer of Sonoace X6 machine (Medison Co., Korea). Placental thickness (PT) (in millimeters), was measured perpendicularly at the level of cord insertion, with the chorionic plate in view. The average of three consecutive measurements was recorded. Fetal parameters, including biparietal diameter (BPD), abdominal circumference (AC), and femur length (FL), were also measured. Fetal weight (in gram) was estimated by the scanner by a combination the measured fetal parameters (BPD, AC, and FL), using the Hadlock formula.  This is illustrated in [Figure 1], [Figure 2], [Figure 3] and [Figure 4]. All measurements were done by the corresponding author.
|Figure 1: Sonogram of fetal head showing measurement of biparietal diameter|
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|Figure 3: Fetal abdominal sonogram for measurement of abdominal circumference|
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|Figure 4: Longitudinal scan of the placenta for measurement of placental thickness|
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The measured parameters were entered into a Microsoft spreadsheet and analyzed with the Statistical Package for the Social Science SPSS version 16 (SPSS incorporated, Chicago). Correlation between EFW and placental thickness was assessed by the Spearman's method. Linear regression was also done for the two variables. Values with P ≤ 0.05 were considered as significant.
| Results|| |
A total of 420 apparently healthy pregnant subjects was examined by ultrasound. The mean age of the study subjects was 29.1 ± 4.9 years. The mean maternal weight was 71.4 ± 13.6 kg and mean height was 1.6 ± 0.5 m. The mean values for placental thickness and EFW pairs were distributed as follows: [Table 1].
For the second trimester:
15-16 weeks; 22.6 ± 1.9 mm and 164.2 ± 16.9 g; 17-18 weeks; 25.0 ± 0.02 mm and 222.9 ± 40.0 g; 19-20 weeks; 28.3 ± 4.2 mm and 344.1 ± 26.4 g;
21-22 weeks; 29.7 ± 5.1 mm and 482.1 ± 50.2 g; 23-24 weeks; 31.6 ± 3.7 mm and 645.7 ± 64.9 g; 25-26 weeks; 31.9 ± 3.1 mm and 884.4 ± 57.5 g.
For the third trimester, the pair distributions were as follows:
27-28 weeks; 33.8 ± 2.7 mm and 1149.6 ± 68.0 g;
29-30 weeks; 37.1 ± 5.5 mm and 1457.6 ± 145.6 g; 31-32 weeks; 34.8 ± 4.4 mm and 1691.8 ± 171.91 g; 33-34 weeks; 38.9 ± 5.8 mm and 2248.1 ± 154.7 g;
35-36 weeks, 41.2 ± 9.4 mm and 2501.2 ± 520.0 g;
37-38 weeks, 39.3 ± 3.6 mm and 3016.6 ± 378.6 g.
The mean values of placental thickness (PT) and EFW throughout gestation were 35.5 ± 7.0 mm and 1555.0 ± 1004 g; respectively.
Spearman's correlation value for the PT and EFW pairs throughout gestation was 0.668 with a P = 0.000. The regression value was 0.586, at P = 0.000.
[Figure 5] in the scatter diagram for the pairs of PT and EFW throughout gestation. It shows a linear relationship between these values.
|Figure 5: Sample report of foetal weight estimation by the Osaka University formula.|
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| Discussion|| |
Placenta thickness in this study was fairly linear throughout the second trimester, with the same pattern maintained in the third trimester. This pattern has been observed in previous studies.  As expected, EFWs showed a progressive increase in value throughout gestation.
This study found a mean placental thickness of 22.6 mm at 15 weeks gestation to 39.2 mm at 39 weeks. The mean estimated fetal weight ranged from 147.0 g at 15 weeks to 3187.4 g at 39 weeks gestation. The correlation and probability values were 0.668 and 0.000 respectively. This corresponding relationship between placental dimensions and EFW was also observed in a Brazilian study by De Paula et al.  Daskalis et al.  in a study among Greek women also reported that placental size may be a useful predictor of neonatal weight, while Sanin et al.  in Mexico examined the relationship between birth weights and placental weights in newborn, and found placental weight to be a predictor of birth weight. Habib  in a study among Saudi women reported that the probability of a normal birth weight increases with increase in placental thickness and diameter [Figure 6].
|Figure 6: Scatter diagram of placenta thickness (mm) versus estimated foetal weight.(g)|
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Abu et al.,  in a study among Nigerian women also noted significant positive correlation between placental thickness and EFW in the second and third trimesters.
A previous study had suggested the predictability of placental weights from placental thickness on two-dimensional ultrasound, using volumetric calculations.  It must be noted, however, that placental volumetric calculations on two-dimensional ultrasound are fraught with errors, since the measurements are not direct and the assumption is based on the placenta being a sphere, the shape to which it approximates.
This study has established nomogram of placental thickness according to gestational age and EFW. Thus, reference values of both placental thickness and ultrasound EFW are given. These values could be useful for comparison when dealing with high-risk pregnancies. However, the observed changes in placental thickness values for a particular estimated gestational age poses a limitation to its usefulness. Therefore, more extensive studies are suggested, further to assess how applicable these findings are in clinical practice.
| Conclusion|| |
This study has indicated a probable linear relationship between placental thickness and ultrasound EFW. It may thus be possible to predict deviations from norms of birth weight in late pregnancy from ultrasound estimated placental thickness.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]