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CORRELATION OF SONOGRAPHIC PLACENTAL THICKNESS WITH GESTATIONAL AGE IN NORMAL SINGLETON PREGNANCIES.

Byline: Aisha Kiran, Muhammad Nafees and Ghulam Abbas

Abstract

Objective: The main objective of the study is to determine the correlation of sonographic mean placental thickness in mm with the composite mean 2nd and 3rd trimester gestational age in weeks estimated by ultrasound.

Study Design: Cross sectional.

Place and Duration of Study: Radiology department, Military hospital, AFIRI Rawalpindi for the period of six months from 10/10/13 to 10/5/14.

Material and Methods: The instrument used in this study was Aloka SSI 5500 ultrasound equipment with 3.5MHz curvilinear transducer. A total of 200 women were included through radiology outdoor with singleton pregnancy in 2nd and 3rd trimester. The fetuses were observed for gestational age estimation using bi-parietal diameter (BPD) and femur length (FL) in the second trimester and BPD, FL and abdominal circumference (AC) in the third trimester. The composite average of the gestational age estimated by the various growth parameters were taken for each fetus and was calculated automatically by the ultrasound software. The placenta was localized in longitudinal section and its antero-posterior thickness measured at the level of insertion of the umbilical cord.

Results: A total of 200 women with singleton pregnancy in 2nd and 3rd trimester were included in this study. The mean age of the women was 25.43+-2.63 years, average gestational age and placental thickness was 26.18+-7.91 weeks and 29.10+-7.027 mm. Total of 104(52%) patients were in2nd trimester and 96(48%) were in 3rd trimester. A linear relationship was observed between gestational age and placental thickness. There were 104 women with 2nd trimester, correlation between placental thickness and gestational age was positive and significant (r=0.959 and p=0.0005) , similarly 96 women with 3rd trimester, correlation between placental thickness and gestational age was positive and significant (r=0.858 and p=0.0005). Strong positive correlation between placental thickness and gestational age was observed (r= 0.985 and p= 0.0005).

Conclusion: Positive correlation suggested that as placental thickness increases, the fetal weight also increases so that the placental growth directly influences the fetal weight.

Keywords: Gestational age, Placenta, Second trimester, Ultrasonography

INTRODUCTION

Placenta is the vital support organ for the developing fetus which provides the physiological link between a pregnant woman and the fetus1. The placenta is a highly vascularized organ and its main functions are supplying of nutrient, oxygen, and hormones to the fetus2. The placenta is formed by the interaction of decidua basalis of the endometrium and chorionic villi of the fetus atimplanation site at about 8-10 weeks. True definition of placenta is possible at about 10-11weeks after conception3.

The placental thickness can be a useful sonographic parameter. It tends to gradually increase with gestational age in a linear fashion (~ 1 mm per week) and therefore the thickness in mm can approximate the gestational age (in weeks). The normal placental AP measurement of the anterior placenta in second trimester >33mm and posterior placenta >40mm should be considered thick4 and associated with a poor outcome in term of perinatal mortality and growth restriction5.

Placental thickness appears to be a promising parameter for estimation of gestational age of the fetus as was also shown in animal studies6. There was a strong positive correlation between placental thickness and gestational age7 (Pearson correlation coefficient r = 0.609, 0.812 and 0.814 in first, second and third trimesters respectively; p= 0.01). He also concluded that subnormal placental thickness for a particular gestational age may be the earliest sign of intrauterine growth. No local data on the subject was available in the last five years.

The measurement of the placental thickness is an important parameter for estimation of fetal age along with other parameters especially in the late mid trimester and early third trimester, where the exact duration of pregnancy is not known and other sonographic parameters also become less reliable . But it is not routinely done locally and if correlation is established then it could be recommended in local practice.

Rationale of the study is to determine the correlation of sonographic mean placental thickness in mm with the composite mean 2nd and 3rd trimester gestational age in weeks estimated by ultrasound.

MATERIAL AND METHODS

This Cross sectional descriptive study was carried out at Armed Forces Institute Of Radiology and Imaging (AFIRI), Military Hospital, Rawalpindi. The study was carried out over a six month duration starting from the 10/10/13 to 10/5/14. Patients with known LMP(last mestrual period), viable singleton pregnancy and in second and third trimester of gestation were included in the study whereas patients havingtwin pregnancy,history of previous IUGR or adverse fetal outcome, coexistent palcental pathology, uterine or adnexal mass, PIH, polyhydramnios or oligo hydramnios, history of immune or non immune hydrops and gestational age of > 40 weeks were excluded from the study.

The sample size was calculated using the software StatsDirect (Menu location: Analysis_Sample Size_Correlation.). Karthikeyan T in 20127demonstrated that there was a linear correlation of placental thickness with gestational age. (Pearson correlation coefficient = 0.812 in second trimesters). Sample size was 200 patients and sampling technique was non probability purposive sampling Approval of the study was taken from the hospital ethical review committee.

Informed consent was taken from the patients before recruitment into the study. The patients were recruited through the radiology outdoor from the patients who are being referred for routine ante natal ultrasound. Patients with their blood pressure and plasma random glucose checked and a history of hypertension, diabetes, previous adverse fetal outcome, intrauterine growth retardation and fetal hydrops were sought. On history the LMP (last menstrual period) date was ascertained and gestational age was calculated by LMP using the Naegle's rule.

Sonography was carried out on each subject included in the study using Aloka SSI 5500 ultrasound equipment with 3.5MHz curvilinear transducer. The fetuses were observed for gestational age estimation using bi-parietal diameter (BPD) and femur length (FL) in the second trimester and BPD, FL and abdominal circumference (AC) in the third trimester. The composite average of the gestational age estimated by the various growth parameters were taken for each fetus and was calculated automatically by the ultrasound software. The placenta was localized in longitudinal section and its anteroposterior thickness measured at the level of insertion of the umbilical cord. All the information was recorded in the proforma attached as Annex I.

Data analysis procedure

Data was analyzed on computer using SPSS 16 (Statistical software package for social sciences). Quantitative data included was placental thickness and gestational age. Values were expressed as mean +standard deviation. Pearson's correlation coefficient (r) of +1-1 was used to measure the correlation of mean gestational age in 2nd and 3rd and mean placental thickness. p< 0.05 was indicated as statistically significant.

Table-1: Descriptive statistics of the study variables

###Variables

Statistics###Placental

###Gestational

###Age (Years)###Thickness

###Age (Weeks)

###(mm)

Mean###25.43###26.18###29.10

95% Confidence###Lower Bound###25.06###25.07###28.12

Interval for Mean###Upper Bound###25.79###27.28###30.08

Median###25###25###27.7

Std Deviation###2.63###7.91###7.027

Inter quartile Range###3###12###11.9

Table-2: Correlation of sonographic mean placental thickness and gestational age estimated by ultrasound.

###Pearson's Correlation

###between placental

###n###p-value

###thickness and gestational

###age

Overall###200###0.985###0.0005

2nd Trimester###104###0.959###0.0005

3rd Trimester###96###0.858###0.0005

RESULTS

A total of 200 women with singleton pregnancy in 2nd and 3rd trimester were included in this study. Histogram of age distribution of the patients is presented in fig-1.

The mean age of the women was 25.43+-2.63 years. Similarly average gestational age and placental thickness was 26.18+-7.91 weeks and 29.10+-7.027 mm as presented. Regarding trimester of the women, 104(52%) were with 2nd trimester and 96(48%) were in 3rd trimester.

A linear relationship was observed between gestational age and placental thickness. Similarly according to 2nd and 3rd trimester linear relationship was also observed.

In table-2, Strong positive correlation between placental thickness and gestational age for the whole sample was observed (r= 0.985 and p=0.0005). There were 104 women with 2nd trimester, correlation between placental thickness and gestational age was positive and significant (r=0.959 and p=0.0005), similarly 96 women with 3rdtrimester, correlation between placental thickness and gestational age was positive and significant (r=0.858 and p=0.0005) as shown in table-2.

DISCUSSION

The best possible antepartum care and the successful deliveries of babies always revolve around the accurate knowledge of the Gestational Age (GA). The gestational age is of utmost importance in the interpretation of biochemical tests such as the screening for the expanded maternal serum biomarkers (Human Chorionic Gonadrotrophin, Alfa Feto protein and the oestrogen and progestrone levels) for the risk assessment of various fetal anomalies, in evaluating the fetal growth by distinguishing the normal from the pathological fetal development.

The placenta is a fetal organ with important metabolic, endocrine and immunological functions besides being responsible for nutrition, respiration and excretion for the fetus. Lastly acting as a barrier, it has a role in protecting the fetus from noxious agents8. Placental formation begins in the later half of the 2ndmonth of the pregnancy and is usually completed by the 4thmonth. It reaches its maximum growth at term9. Placental thickness is not diagnostic of any particular condition but can contribute to the management of high risk pregnancies10. Placental thickness of <2.5 cm is associated with intrauterine growth retardation while thick placenta are associated with maternal diabetes mellitus, foetalhydrops and intra uterine foetal infection. The usefulness of this relationship between placental thickness for a gestational age may be the earlist indication of foetal growth retardation11.

In our study the fetus was observed for gestational age estimation using biparietal diameter (BPD) and femur length (FL) in the second trimester and BPD, FL and abdominal circumference (AC) in the third trimester.

In our study strong positive correlation between placental thickness and gestational age for the whole sample was observed (r= 0.985 and p= 0.0005). Tongsong T; Boonyanurak P et al2 did a regression analysis which yielded the following linear equation of the relationship: placental thickness (in mm) = gestational age (in weeks) x 1.4-5.6 (r=0.82).Christopher ChukwuemekaOhagwu et al13 demonstrated in Nigerian women that there is significant and strong positive correlation between placental thickness and gestational age. They also concluded that placental thickness appears promising as an accurate indicator of gestational age in singleton pregnancies. In a study by Elchalal, Ezra et al in 2000, Placental thickness was determined by routine sonographic examination throughout the pregnancy in 561 normal singleton pregnancy. A linear increase of placental thickness was found to correlate with gestational age throughout the pregnancy14.

Mital P, Hooja N, Mehndiratta K.et al15concluded, that the measurement of placental thickness is an important parameter for estimation of fetal age. It is helpful in cases where the exact duration of pregnancy is not known (especially between the 22ndweek and 35th week) where the placental thickness almost matches with the gestational age. Anupama Jain, Ganesh Kumar, U Agarwal, S Kharakwal et al16 reported that the value of mean placental thickness increases with advancing gestational age and almost matched the gestational age from 27 to 33 weeks. Tanawattancharoen et al17 reported less variation in placental thickness at gestational age between 18 and 41 weeks. Jauniax et al18 have established correlation between placental size and gestational age.

CONCLUSION

To conclude, we can say that the measurement of the placental thickness is an important parameter for estimation of fetal age along with other parameters especially in the late mid trimester and early third trimester where the exact duration of pregnancy is not known and other sonographic parameters also become less reliable in this part of gestation. This positive correlation suggested that as placental thickness increases, the fetal weight also increases so that the placental growth directly influences the fetal weight.

CONFLICT OF INTEREST

The study has no conflict of interest to declare by any author.

REFERENCES

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8. Cunningham FG, Gant NF, Leveno KS, Gilstap LC, Hanth JC, Wenstrom KD. Williams's obstetrics. 21st ed. Ne w York: McGrewHill; 2001.

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12. Ohagwu CC, Abu PO. Placental thickness: a sonographic indicator of gestational age in normal singleton pregnancies. Nigeria Inter J Med Update. 2009;4(2):9-14.

13. Elchalal U1, Ezra Y, Levi Y, Bar-Oz B, Yanai N, Intrator O, et al. Sonographically thick placental: Marker for increased perinatal risk - A prospective cross-sectional study". Placenta. 2000 Mar-Apr;21(2-3):268-72.

14. Mital P, Hooja N, Mehndiratta K. Placental thickness: a sonographic parameter for estimating gestational age of the fetus. Indian J Radiol Imaging. 2002; 12:553.

15. Jain A, Kumar G. Placental thickness - a sonographic indicator of gestational age in normal singleton pregnancies in Nigerian women. Inter J Med Update. 2009 Jul; 4(2):9.

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17. Jauniaux E, Ramsay B. Ultrasonographic investigation of placental Morphology and size during second trimester of pregnancy. Am J Obstet Gynecol. 1994;170:130-7.
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Publication:Pakistan Armed Forces Medical Journal
Article Type:Report
Date:Feb 29, 2016
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