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ORIGINAL ARTICLE
Year : 2019  |  Volume : 32  |  Issue : 4  |  Page : 1406-1410

Correlation between second and third trimester placental thickness with ultrasonographic gestational age


Department of Obstetrics and Gynecology, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission03-Dec-2018
Date of Decision31-Dec-2018
Date of Acceptance08-Jan-2019
Date of Web Publication31-Dec-2019

Correspondence Address:
Mohammed A Zerban
Shebien Elkom, Elmounfia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_389_18

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  Abstract 


Objectives
The objective of this study was to evaluate the correlation between placental thickness in the second and third trimesters with gestational age, weight, and fetal outcome.
Background
Ultrasonography enables the evaluation of the placenta and the detection of placental abnormalities using different parameters such as placental thickness and volume or special techniques like three-dimensional power Doppler.
Materials and methods
This cohort study was conducted at the Departments of Obstetrics and Gynecology of Menoufia University Hospitals and Shebien Elkom Teaching Hospital from June 2017 to May 2018. This cohort study comprised 100 pregnant women who were attending the antenatal clinic at 24 weeks and were followed-up at 32 and 36 weeks. Detailed history was taken to rule out medical and surgical illnesses that could affect the study. Thorough general, physical, and obstetrical examinations were carried out. US examinations were performed at three visits: first between 24 and 28 weeks, second between 28 and 32 weeks, and third between 32 and 36 weeks.
Results
There was a significant positive correlation between placental thickness and birth weight in the second and third trimesters. The mean age of cases was 28 ± 5 years. Mean birth weight was 3243 ± 402 g, and mean placental weight was 511 ± 64 g. US measures of placental thickness in the first, second and third visit were 24.91 ± 1.27, 29.50 ± 1.23, and 34.60 ± 1.6 mm, respectively.
Conclusion
Measurement of placental thickness by ultrasonography is a good predictor tool for estimating the fetal weight.

Keywords: fetal, gestational age, placenta, ultrasound, weight


How to cite this article:
Abdelhamid AN, Sayyed TM, Shahin AE, Zerban MA. Correlation between second and third trimester placental thickness with ultrasonographic gestational age. Menoufia Med J 2019;32:1406-10

How to cite this URL:
Abdelhamid AN, Sayyed TM, Shahin AE, Zerban MA. Correlation between second and third trimester placental thickness with ultrasonographic gestational age. Menoufia Med J [serial online] 2019 [cited 2020 Feb 24];32:1406-10. Available from: http://www.mmj.eg.net/text.asp?2019/32/4/1406/274269




  Introduction Top


Fetal well-being is affected by many factors, but a healthy placenta is the single most important factor in producing a healthy baby. Placenta is the organ that provides oxygen and nutrients to the fetus. Adequate fetal growth and subsequent optimal birth weight depend on a proper functioning placenta [1]. Fetal weight estimation is important because birth weight is shown to be the single most important parameter that determines neonatal survival [2]. The placental development starts at the seventh day after fertilization when the first cell layer of the cytotrophoblast is observed. During pregnancy, a range of problems may occur that could lead to fetal abnormalities and death. The most important of them is placental abnormalities [3]. The placenta is a fetomaternal organ that nourishes and protects the fetus, and it dies after the delivery of the baby; it acts like a mirror reflecting the status of both the mother and the fetus. The term placenta averages 22 cm (9 inches) in diameter and 2–2.5 cm (0.8–1 inch) in thickness, with the greatest thickness at the center and becomes thinner peripherally [4]. The placenta has a maternal surface that is divided into lobules or cotyledons with irregular grooves or clefts and a fetal surface, which is smooth, shiny, and translucent and covered with the amniotic membrane [5]. The surface area of the placenta explains the efficacy of the placenta to transfer the amount of nutrients, oxygen, and carbon dioxide that passes from the mother to fetus. Placental surface area growth is completed by the third trimester, whereas the placental thickness growth continues until the late third trimester [6]. Placental thickness is very much related to fetal development and may be a key in perinatal outcome. According to Sadler et al. (2004), at term, the placenta is ~3 cm thick and measures 15–25 cm in diameter. A 'warning limit' of placental diameter of 18 cm and placental thickness of 2 cm at 36 weeks predicts low-birth weight neonates [7]. Small placentas are associated with pre-eclampsia, chromosomal abnormalities, severe maternal diabetes mellitus, chronic fetal infections, and intrauterine growth restriction [8]. The placentas over 4 cm thick at term have been observed in conditions like diabetes mellitus, perinatal infections, and hydrops fetalis (both immune and nonimmune) [9]. The incidence of perinatal morbidity and mortality was considerably higher among pregnant women with thick placenta, related to higher rates of fetal anomalies and higher rates of both small for gestational age and large for gestational age neonates at term [10]. The aim of this study was to evaluate the correlation of placental thickness in the second and third trimesters with gestational age, weight, and neonatal outcome.


  Materials and Methods Top


This cohort study was conducted at the Departments of Obstetrics and Gynecology of Menoufia University Hospitals and Shebien Elkom Teaching Hospital from June 2017 to May 2018. Before commencing this study, an approval has been obtained from the Research Ethics Committee of Menofia Faculty of Medicine and Shebien Elkom Teaching Hospital. Participants' consents were received after explanation of the study protocol. The study cohort comprised 100 pregnant women attending the antenatal clinic at 24 weeks, and they were followed-up at 32 and 36 weeks. Inclusion criteria were as follows: known last menstrual period that was compatible with first trimester ultrasound, singleton pregnancy, and age group of 20–35 years. Exclusion criteria were as follows: patients who were not sure of dates or with a history of irregular cycles, fetal anomalies, patients with chronic medical diseases like diabetes, hypertension, and chronic renal disease, multiple pregnancy, low-lying placenta or placenta previa, difference of more than 4 weeks between period of amenorrhea and fundal height, and placental abnormalities.

The composite assessment of gestational age was carried out by measuring the biparital diameter (BPD), head circumference, abdominal circumference (AC), and femur length (FL). Estimated fetal weight (EFBW) was determined by measurement of BPD, AC, and FL, adopting the formula devised by Hadlock. The neonatal outcome (Apgar score, weight) was recorded together with weighing the placenta. According to neonatal weight, there were two groups (the first group comprised newborns >2500 g, whereas the second group included newborns <2500 g). The primary outcome included the correlation between placenta thickness and fetal gestational age and weight at the second and third trimesters. The secondary outcome was the relationship between recorded placental thickness in the second and third trimesters and neonatal outcome measures. Detailed history was taken to rule out medical and surgical illnesses that could affect the study. Thorough general, physical, and obstetrical examinations were carried out. Ultrasound examinations were performed at three visits: first was between 24 and 28 weeks, second was between 28 and 32 weeks, and third was between 32 and 36 weeks.

Scanning technique

The placenta was identified as a hyperechoic area separated from the fetus by a hypoechoic area of amniotic fluid. The two edges of the placenta were focused in a single ultrasound field in transverse and longitudinal sections. The probe was moved all over the localized placenta, and the level of cord insertion was identified over the fetal surface. All sonographic examinations were performed transabdominally by one experienced sonographer in Shebien Elkom Teaching Hospital by using vulson s6 with a 4–9 MHz curved transducer.

Sample size

The required sample size has been calculated using IBM Sample Power, version 3 (IBM Corp., Armonk, New York, USA).

The primary outcome measure is the correlation between placental thickness and birth weight.

A previous study reported that the coefficient of correlation between the birth weight and the placental thickness at the second or third trimester was 0.15 or 0.14, respectively [10].

Accordingly, it is estimated that a sample size of 94 patients would be required to achieve a power of 80% (type II error, 0.2) for detection of statistical significance as regards the correlation between third trimester placental thickness and birth weight. The coefficient of correlation (r) between third trimester placental thickness and birth weight is assumed to equal zero under the null hypothesis and to equal 0.14 under the alternative hypothesis [10].

Statistical analysis

Data were analyzed using MedCalc, version 15.8 (MedCalc Software bvba, Ostend, Belgium). Numerical variables were presented as mean ± SD and categorical variables as number and percentage. Simple linear regression was used to derive a prediction rule (equation) for estimation of actual birth weight from placental thickness. Accuracy of placental thickness for estimation of the actual birth weight or placental weight was assessed by calculation of the SE of the estimate, which is calculated as follows:



where SE (est) is the SE of the estimate, Y is the VSD (device) size, Y' is the estimated VSD size, Σ (Y-Y') is the sum of squared differences, and N is the total sample size.

Receiver-operating characteristic curve analysis was used to obtain a cut-off of placental thickness and area to predict fetal weight abnormalities.


  Results Top


The present study was conducted in the Department of Obstetrics and Gynecology of Shebien Elkom Teaching Hospital in collaboration with the Department of Radiology. A total of 100 women were included in the study. The mean maternal age in our study was 28.46 ± 4.6. Women were in the group range of 19–38 years [Table 1]. The maternal BMI in our study was ranged from 21 to 36 with Mean ± SD was 27.82 ± 3.2 [Table 1]. The mean BPD1, FL1, and AC1 in the first visit were 24.8 ± 1.5 mm, 25 ± 1.6, and 23.7 ± 1.2 [Table 2]. The mean placental thickness in the first visit was 24.91 ± 1.27 mm. The mean EFBW by Hadlock in the first visit was 700.40 ± 120.5 g. In the second visit, the mean BPD2, FL2, and AC2 were 29.39 ± 1.33, 28.71 ± 1.34, and 28.33 ± 1.42 [Table 3]. The mean EFBW by Hadlock in the second visit was 1372.30 ± 306. The mean placental thickness in the second visit was 29.50 ± 1.23 mm. In the third visit, the mean PBD3, FL3, and AC3 values were 34.70 ± 1.5, 33.90 ± 1.5, and 33.56 ± 1.8, respectively [Table 4]. The mean placental thickness in the third visit was 34.60 ± 1.6 mm. The mean EFBW by Hadlock in the third visit was 2516.40 ± 311. A regression equation was formed from simple linear regression analysis for determination of EFBW by using placental thickness; thereafter, the result was compared with EFBW by Hadlock. The mean EFBW by Hadlock was 700.40 ± 120.5 g. In the first visit and in the second visit, it was 1372.30 ± 306 g, and, in the third visit, it was 2516.40 ± 311 g.
Table 1: Characteristics of the study population age, BMI, and parity among the participants in the studied group (n=100)

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Table 2: Placental thickness, biparital diameter, femur length, and abdominal circumference and estimated fetal weight in the first visit (24-28 weeks)

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Table 3: Placental thickness, biparital diameter, femur length, and abdominal circumference and estimated fetal weight in the second visit (28-31 weeks)

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Table 4: Placental thickness, biparital diameter, femur length, and abdominal circumference and estimated fetal weight in the third visit (32-36 weeks)

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When we measured EFBW by regression formula using Placental thickness (PT), there was no significant difference between EFBW using either Hadlock or regression formula. Hence, we can use our regression formula instead of Hadlock formula in measuring EFBW by ultrasound [Table 5]. We can use the regression formula as follows:
Table 5: Weight estimated from the formula

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a constant B slope of regression X placental thickness

From ( first visit) weight = −1154.53 + 74.46* placental thickness.

From (second visit) weight = −3946.60 + 180.3* placental thickness.

From (third visit) weight = −1571.6 + 118.2* placental thickness.

In our study, the best cut-off points for prediction of small for gestational age babies is when placental thickness less than or equal to 2.5 cm and less than or equal to 2.7 cm, and less than or equal to 3.5 cm with sensitivity 100% all through pregnancy and specificity 65% and 100% and 100% and accuracy 66.7% and 100% and 100% in groups 1 and 2 and 3, respectively, and according to PA less than or equal to 35 cm 2 and less than or equal to 38 cm 2 or less than or equal to 48 cm 2 with sensitivity 100% and 100% and 26.9% and specificity 96.2% and 100% and 42.3% and accuracy 96.2% and 100% and 44.4% in groups 1 and 2 and 3, respectively [Table 6] and [Table 7]. The neonatal outcome of our study, which depends on (Apgar score, weight) show 90 babies their weights were more than 2500 g and another 10 babies their weights less than 2500 g, and 83 babies their Apgar score were more than 8 and did not need neonatal ICU. The other 17 babies need neonatal ICU.
Table 6: Receiver-operating characteristic curve for detection of placental thickness in the second visit cutoff with regard to low-birth weight (ill1)

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Table 7: Receiver-operating characteristic curve for detection of placental thickness in the third visit cutoff with regard to low-birth weight (ill2)

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  Discussion Top


In the current study, the mean age of the included women was 28.4, and the mean BMI was 27.8 kg/m 2. The mean placental thickness in the first visit was 24.91 ± 1.27 mm, in the second visit it was 29.50 ± 1.23 mm, and in the third visit it was 34.60 ± 1.6 mm. The mean EFBW by Hadlock in the first visit was 700.40 ± 120.5 g, in the second visit it was 1372.30 ± 306 g, and in the third visit it was 2516.40 ± 311 g. The current study results showed a significant positive correlation between placental thickness with EFBW by Hadlock, and these results were similar to Noor et al. [11] who evaluated placental thickness at 18–40 weeks of gestation and found a significant positive correlation between placental thickness and EFBW. Moreover, our results are similar to Ismail et al. [12] who found a significant positive correlation between placental thickness and EFBW. In a study in 2015 conducted by Baghel et al. [13], it was observed that there was a significant positive correlation between placental thickness and EFBW and birth weight. EFBW increased with placental thickness. In a study by Afrakhteh et al. [14], which was carried out to investigate the relationship between placental thickness during the second and third trimesters and birth weight, and which included 250 singleton pregnant women who presented for antenatal care, a significant positive correlation between placental thickness and birth weight in the second and third trimester was found. Habib et al. (2002) concluded that ultrasonographic placental diameter and thickness measurements seemed to be of prognostic value in identifying the subsequent occurrence of intrauterine growth retardation [15]. In this study, placental thickness on ultrasound, at 32 and at 36 weeks, had a significant positive correlation with EFBW. Abu et al. (2009) investigated the relationship between placental thickness and EFBW [16]. A total of 645 pregnant Nigerian women in low-risk pregnancies in the second and third trimesters were recruited. There was a significant positive correlation between measured placental thickness and EFBW in both the second and third trimesters of pregnancy. In our study, the results were similar to Afrakhteh et al. [14]. They found that women with placental thickness less than or equal to 2.7 cm and less than or equal to 3.7 cm in the second and third trimester, respectively, bear smaller babies. This is similar to the study by Elsafi et al. [17]. They found that placental thickness of less than 2.5 cm during the third trimester is considered less than normal and might be an indication of intrauterine growth restriction.

Furthermore, these results are nearly similar to Habib et al. (2002). They used placental thickness of less than 2 cm at 36 weeks' gestation as a sensitive cut-off point for prediction of low-birth-weight infants.


  Conclusion Top


Measurement of placental thickness by ultrasound is a good predictor tool for estimating the fetal weight. Increased placental thickness is not diagnostic of any specific disorder but may contribute to the management of a fetus at risk.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Afrakhteh M, Moeini A, Taheri MS, Haghighatkhah HR. Correlation between placental thickness in the second and third trimester and fetal weight. Rev Brasil Ginecol Obstet 2013; 35:317–322.  Back to cited text no. 14
    
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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