|Year : 2020 | Volume
| Issue : 2 | Page : 138-144
Relationship of placental diameter and thickness versus fetal growth biometrics: A cross-sectional sonographic evaluation of antenatal women in Enugu, Southeast Nigeria
Ozoemena Joseph Ogbochukwu1, Ngozi Regina Dim2, Amaka Obiageli Nnamani2, Ngozi Rosemary Njeze2, Emmanuel Nebeuwa Obikili3, Cyril Chukwudi Dim4
1 Department of Radiology, Federal Medical Centre, Nguru, Yobe State, Nigeria
2 Department of Radiation Medicine, Faculty of Medical Sciences, College of Medicine, University of Nigeria, Ituku-Ozalla Campus, Enugu, Nigeria
3 Department of Anatomy/Radiation Medicine, College of Medicine, University of Nigeria, Ituku-Ozalla Campus, Enugu, Nigeria
4 Department of Obstetrics and Gynaecology/Institute of Maternal and Child Health, College of Medicine, University of Nigeria, Ituku-Ozalla Campus, Enugu, Nigeria
|Date of Submission||02-Jun-2020|
|Date of Decision||29-Jun-2020|
|Date of Acceptance||15-Jul-2020|
|Date of Web Publication||29-Jul-2020|
Ngozi Regina Dim
Department of Radiation Medicine, College of Medicine, University of Nigeria, Ituku-Ozalla, P.M.B. 01129, Enugu.
Source of Support: None, Conflict of Interest: None
Background: The placenta is a feto-maternal organ that plays a vital role in normal fetal growth and perinatal outcome. Sonographic studies have shown that placental diameter (PD) and thickness (PT) increase linearly with gestational age, and may have relationships with fetal parameters and estimated weight. Aim: To determine the relationship between PT and PD with fetal biometric parameters and estimated weight, as well as establish a model for estimating birth weight from these placental parameters. Materials and Methods: This was a cross-sectional study of 400 antenatal women with normal, third-trimester, singleton pregnancies at the University of Nigeria Teaching Hospital Ituku-Ozalla, Enugu. Ultrasound was used to evaluate their PD and PT. Fetal weight was estimated (EFW) using fetal biparietal diameter, abdominal circumference and femur length. Data were analyzed with SPSS, version 20. Results: The mean PD of participants before 37 weeks of gestation (183.8 ± 8.7 mm) was significantly shorter than that of participants at term (205.7 ± 2.5 mm), P < 0.001. For PT, the mean values for participants before term and at term were 36.3 ± 2.4 mm versus 43.2 ± 1.0 mm, respectively, P < 0.001. There were varying positive correlations between each placental parameter and the three fetal biometric parameters. Both PD and PT had a high positive correlation with EFW (P < 0.001). Regression analysis predicted fetal weight using PD and PT. Conclusion: PD and PT showed a high positive correlation with fetal weight and can be used as a sonographic parameter in estimating fetal weight.
Keywords: Abdominal circumference, estimated fetal weight, placental diameter, placental thickness
|How to cite this article:|
Ogbochukwu OJ, Dim NR, Nnamani AO, Njeze NR, Obikili EN, Dim CC. Relationship of placental diameter and thickness versus fetal growth biometrics: A cross-sectional sonographic evaluation of antenatal women in Enugu, Southeast Nigeria. Int J Med Health Dev 2020;25:138-44
|How to cite this URL:|
Ogbochukwu OJ, Dim NR, Nnamani AO, Njeze NR, Obikili EN, Dim CC. Relationship of placental diameter and thickness versus fetal growth biometrics: A cross-sectional sonographic evaluation of antenatal women in Enugu, Southeast Nigeria. Int J Med Health Dev [serial online] 2020 [cited 2020 Aug 15];25:138-44. Available from: http://www.ijmhdev.com/text.asp?2020/25/2/138/291059
| Introduction|| |
Birth weight is essentially governed by two processes: the duration of gestation and the intrauterine growth rate., The placenta is a feto-maternal organ that plays a vital role in normal fetal growth; its structural development, metabolic function and release of growth hormone-like substances enable it to perform this role and so impact significantly on perinatal outcome.,, Placental thickness (PT) and diameter (PD) are independent and significant variables associated with birth weight towards term. PT is key to perinatal outcome due to its close relationship with fetal development, reflecting the wellbeing of the fetus (and mother). Studies evaluating this relationship demonstrated that decreased PT is associated with pre-eclampsia, chromosomal abnormalities, severe maternal diabetes mellitus, chronic fetal infections and intrauterine growth restriction; and increased thickness observed in pregnancies with perinatal infections, hydrops fetalis and gestational diabetes.,,, Hence, a considerably higher incidence of perinatal morbidity and mortality, relating to higher rates of fetal anomalies and higher rates of both small-for-gestational-age and large-for-gestational-age neonates at term, was associated with increased PT.
Fetal weight estimation (EFW) is key to obstetric practice because birth weight is the single most important factor that determines obstetric outcomes and neonatal survival., Fetal growth and its estimation have been evaluated with varying accuracy using common fetal parameters, which include biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL). These growth parameters can sometimes be adversely affected by insufficient nutrients reaching the fetus through the placenta, especially in pregnancies with growth restriction where PT is reported to be thin. This makes accurate estimates of fetal weight difficult, if relying only on fetal biometric parameters, and so there is a need for other growth parameters such as placental dimensions to supplement estimates of birth weight. Sonographic studies evaluating placental dimensions mostly assessed the relationship of PT with gestational age (GA) or fetal outcomes;,[7-9],, and a few studies in our locality assessed the relationship of fetal weight with PT.,, However, none of these local studies evaluated the relationship between the two placental dimensions and fetal biometric parameters or weight, nor generated a regression formula incorporating both placental parameters. This study was designed to fill these knowledge gaps. Therefore, the study aimed to determine the correlation of PT and PD with fetal biometric parameters as well as EFW. It also derived the regression formulae for EFW using these two placental parameters.
| Materials and Methods|| |
The study was conducted at the antenatal clinic of the Obstetrics and Gynecology Department and the ultrasound suite in the Radiation Medicine Department of the University of Nigeria Teaching Hospital Ituku-Ozalla, Enugu, Nigeria. The hospital is a federal teaching hospital, with antenatal clinics being run every weekday with an average attendance of 795 women per month. The study period lasted from June 2014 to May 2015.
Ethical clearance was obtained from the hospital’s Health Research Ethics Committee, and the study was conducted in accordance with standard ethical procedures, with a written informed consent obtained from all participants.
Sample size calculation
A sample size of 400 participants was adequate to determine the average PT of participants at term using the standard deviation of PT at term (3.6 mm) from a related study, a precision (absolute error) of 0.15 mm at 95% confidence level and a non-response rate of 10%.
Study design and population
This was a cross-sectional study involving 400 consenting eligible antenatal women with normal third-trimester pregnancies. Participants were selected consecutively at the antenatal clinics. Eligibility criteria included all normal singleton pregnancies at a GA of 28–41 weeks that were sure of their last menstrual period. Exclusion criteria included gross uterine/genital anomalies, maternal medical illness such as diabetes mellitus, hypertension, Rhesus iso-immunization, sickle cell disease and other hemoglobinopathies.
B-scale transabdominal ultrasonography, using a SONOSITE M-Turbo mobile machine (made in USA, 2012 model) with a 3.5–5 MHz curvilinear probe, was employed to evaluate fetal parameters, PD and PT in the third trimester. All participants were scanned once during the study period; most scans were done at the Radiation Medicine Department ultrasound suite or occasionally at the antenatal clinic. PD was demonstrated on a transverse scan at the site of umbilical cord insertion, which was confirmed using color Doppler scan. The diameter was measured parallel to the length of the chorionic surface, from the upper to the lower limit of the placenta, using a split-screen, which allowed concurrent measurements of the upper and lower limits of the placenta, which were summed up to get one dimension [see [Figure 1]]. As shown in [Figure 2], PT was taken by measuring perpendicularly at the level of umbilical cord insertion, from the echogenic feto-placental surface (chorionic plate) to the placento-endometrial surface (myometrial interface). Fetal weight was estimated by an in-built sonographic algorithm after measuring fetal BPD, AC and FL on a static ultrasound screen. The algorithm was based on the Hadlock BPD/AC/FL formula, which has been shown to have a high accuracy for EFW in the study area. All measurements were taken twice and an average recorded in millimeters to reduce observer bias.
|Figure 1: Transverse obstetric sonogram demonstrating placental diameter measurement of an anterior placenta on a split screen. *The calipers demonstrate the line of measurement parallel to the length of chorionic surface from the upper to the lower limit of placenta. Concurrent measurements of the upper and lower limits of the placenta, AB and CD, are shown on split screens. These were summed up to get one dimension|
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|Figure 2: Longitudinal obstetric sonogram demonstrating placental thickness measurement of an anterior placenta. *The calipers A–B demonstrate the line of measurement at the level of cord insertion into the placenta|
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Data were analyzed with SPSS, version 20 (IBM Corporation, Armonk, NY, USA). Student t-test was used to compare continuous variables. Pearson’s correlation analysis was used to test for relationships between continuous variables. A linear regression analysis was used to predict birth weight. Statistical tests were considered significant at a P value ≤0.05.
| Results|| |
A total of 400 women at 28–41 weeks of gestation participated in the study, and their data were analyzed. The mean age of participants was 29.3 ± 3.5 (range 20–44) years, and most participants (41.5%, 166/400) were multiparous. The modal GA range at delivery for all participants was 36–40 weeks (68.5%, 274/400).
The mean PD of participants before 37 weeks of gestation (183.8 ± 8.7 mm) was significantly shorter than that of participants at term (205.7 ± 2.5 mm), P < 0.001. For PT, the mean values of participants scanned before term and at term were 36.3 ± 2.4 versus 43.2 ± 0.9 mm, respectively, P < 0.001. As shown in [Table 1] and [Table 2], both PD and PT measurement in the third trimester increased from 28 weeks of gestation, peaked at 39 weeks and then declined slightly through a GA of 40–41 weeks; PD and PT values at 41 weeks of gestation (207.0 ± 2.3 versus 43.5 ± 0.4 mm) remained higher than the corresponding values at 38 weeks (205.0 ± 1.4 versus 43.0 ± 0.0 mm).
|Table 2: Distribution of mean PD, PT, BPD, AC, FL versus GA in third trimester|
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For the fetal parameters in the third trimester, the mean values of BPD, AC and FL increased with GA [Tables 1] and . The mean values of parameters at 28 and 41 weeks were: BPD = 74.9 ± 2.5 versus 96.0 ± 0.8 mm (P < 0.001), AC = 235.4 ± 6.0 versus 373.0 ± 16.3 mm (P < 0.001) and FL = 53.0 ± 1.5 versus 81.0 ± 0.8 (P < 0.001). Likewise, the mean EFW increased as the GA of participants increased. The least mean EFW of 1377.9 ± 362.1 g was identified at 28 weeks of gestation, while the highest mean EFW of 4264.0 ± 180.4 g was recorded at 41 weeks of gestation (P < 0.001).
As shown in [Table 3], Pearson’s correlation analyses showed that both PD and PT had reasonable to high positive correlation with each of the three fetal parameters (BPD, AC and FL; P < 0.001 for all variables). Fetal AC had the highest correlation coefficient with both PD and PT, compared to other fetal biometrics. There was also a high positive correlation of both PD and PT with EFW [Figure 3] and [Figure 4]. However, PT had a higher correlation coefficient (r = 0.764) compared to PD (r = 0.668), P = 0.005. Following a regression analysis, the regression equations expressing the relationships between EFW in grams with PD and PT in millimeters, respectively, are E = 35.4(PD) – 4596.3; and E = 127.4(PT) – 2658.6.
|Table 3: Correlation of placental parameters with fetal biometric parameters and EFW|
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| Discussion|| |
The placenta is a feto-maternal organ that reflects both fetal and maternal status;, therefore, its sonographic measurement provides information on fetal age, weight and growth. As expected, this study showed that PT and PD increased progressively with GA in the third trimester of normal pregnancies; the placenta nourishes the fetus and, thus, should increase in size as the fetus grows with increasing GA. Furthermore, in the study population, a significant difference was observed between mean PT and mean PD values before and at term in this study, which supports a linear increment of these placental dimensions as GA progressed in the third trimester. Thus, this study aligns with the findings of related studies that showed that PT or/and PD are good indicators of GA estimation during pregnancy.,[7-10],,
Sadler in his Textbook of Medical Embryology, referred to by several authors,,,, stated the values of PD and PT at full term as 150–250 and 30 mm, respectively. However, for this study, the mean PD at term was within Sadler’s range, while the mean PT value of 43.2 ± 0.96 mm was higher than his value; though he did not specify the population used to arrive at those values, but it is unlikely to be our study population. Therefore, racial differences may explain the obvious difference between the mean PT values. Given the mean PT at term found by this study, the report by some authors that a PT >40 mm at term was more likely to be associated with gestational diabetes, intrauterine infections and hydrops fetalis,,, may not apply to our environment since our study population did not show these complications. Interestingly, similar studies on populations in Enugu and other parts of southern Nigeria all reported a mean PT >30 mm at term; a study from Enugu had a mean PT of 39.4 ± 3.8 mm; another in Makurdi found a mean PT of 43.5 ± 5.6 mm, which is similar to this study’s mean value, while related studies from Benin and Port Harcourt reported a similar mean PT of up to 39 mm. The pattern of mean PT values at term in this study, characterized by a progressive increase with a slight decrement after reaching a peak, was also found by several other studies.,[8-10],, The explanation for a decline in PT after a peak is not clear, but may be due to placental degenerative processes. Notably, our study observed a slight decline in mean values for both PT and PD. However, this decline in PT/PD values seen after 39 weeks did not exceed the values obtained at 38 weeks, probably because the pregnancies were not allowed to exceed beyond 41 weeks of gestation. These observations call for further studies.
Correlation analyses established that both PD and PT had a high positive correlation with the three fetal biometric parameters (BPD, FL and AC) used in this study to estimate fetal weight. Therefore, it is not surprising that the placental parameters were also positively correlated with EFW in the study, which demonstrates a linear growth of the placenta with fetal growth. This finding may support the observation by Habib that an increase in PT and PD in the second half of pregnancy might increase the probability of an infant having a normal birth weight. As found by two other studies that evaluated PT with fetal parameters,, this study similarly showed that AC had the strongest positive correlation with both PD and PT. A study involving the same target population found that the EFW module used in this study, which involved BPD, FL and AC, predicted birth weight with the highest accuracy; so, it may follow that since PD and PT were positively correlated with the three fetal parameters, the regression formula generated for both of them in this study may be relevant for the determination of EFW that predicts birth weight with good accuracy. Nevertheless, further studies are required to validate the accuracy of each formula as a predictor of birth weight. The formulae are very simple. Thus, if validated, they will have a practical application in our resource-poor setting by reducing the rampant false prediction of birth weight by EFW. The importance of the relationship of EFW with PD and PT in clinical practice is highlighted by Adeyekun and Ikubor, who indicated that as placental size is a known independent predictor of fetal weight, in cases of high-risk pregnancies, placenta size and fetal weight can be compared, especially when it is difficult to accurately determine GA. Because PT had a significantly higher correlation with EFW than PD in this study, PT may be a better variable than PD in the derivation of EFW in the third trimester from placental parameters in the study environment.
The study was cross-sectional and restricted to normal pregnancies within the third trimester, which may affect its generalization especially to pregnancies below 28 weeks of gestation. A large longitudinal study across second and third trimesters is, therefore, recommended. However, despite this limitation, the study is strengthened by the quality assurance mechanism employed during ultrasound measurements, which would have minimized measurement bias.
Also, the formulae for estimating EFW using PT and PD generated by the study are yet to be validated, but are novel and simple modules yet to be explored within and outside Nigeria.
| Conclusion|| |
Mean PT and PD in the third trimester increased with GA of antenatal women in Enugu, Nigeria. Compared to PD, PT had a stronger positive correlation with EFW derived from fetal BPD, FL and AC. Also, the regression formulae for EFW in third-trimester pregnancies were developed using PT and PD. Therefore, PD and PT can be employed as additional and easy-to-use sonographic parameters for estimating the fetal weight of normal third-trimester pregnancies in women in Enugu.
We acknowledge the research assistants, technical staff and resident doctors in the Radiation Medicine Department ultrasound suite of the University of Nigeria Teaching Hospital Ituku-Ozalla (UNTH), Enugu. We appreciate the resident doctors, the head and nursing staff of the antenatal clinic at the Obstetrics and Gynecology Department of UNTH, who made recruitment of participants seamless.
The manuscript is an excerpt from the dissertation submitted by the first author for a Fellowship of West African College of Surgeons examination in 2015.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]