ABSTRACT
Recent studies have suggested an association of placenta thickness with gestational age in the second and third trimester of pregnancy. But the relationship of placenta thickness according to sex, its relationship to other foetal characteristic within the second and third trimester and somematernal anthropometric variables has not been evaluated. This study consisted of 921 normal pregnancies divided into second (n = 468) and third (n = 453) trimester. Information on maternal age, weight, height and menarcheal age, digit length of hands, hand breadth, hand length, leg breadth and leg length were obtained including foetal parameters such as femoral length (FL), biparietal diameter (BPD), head circumference (HC), occipitofrontal diameter (OFD), abdominal circumference (AC), gestational age (GA), foetal weight (FW) and placenta thickness (PT). Foetal parameters and gestational age were measured in compliance with the Hadlock methodand placenta thickness with the method of Hoddick.Maternal hand and foot measurements were done according to the method of Manning. Independent sample t-test, one-way Analysis of variance (ANOVA), Pearson‘s correlation, partial correlation and multiple linear regression were used. P < 0.05 was set at the level of significance. The mean of maternal weight and foetal parameters between second and third trimester gestation showed significant difference (p< 0.05). Subjects were divided into groups based on their parity, level of education and ethnicity. Foetal parameters were classified according to sex. Foetal parameters and placenta thickness showed no significant difference according to parity. Level of education and ethnicity showed significant difference on AC, FW and PT. But there was also no significant difference in foetal and placenta thickness according to sex of the foetus even though male foetuses had higher values except for placenta PT where that of female foetuses was a few millimetres higher. There was significant positive relationship between
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placenta thickness and foetal growth parameters including foetal weight (p< 0.001). 2D:4D ratio of the right hand showed a significant relationship with some foetal growth parameters in the third trimester. Also, foot breadth showed significant relationship with some foetal growth parameters in both second and third trimester. Placenta thickness could predict gestational age (R2 = 0.045) and (R2 = 0.156) in the second and third trimester gestation respectively.Also, placenta thickness was a good predictor of foetal weight (R2 = 0.057) and (R2 = 0.158) for second and third trimester gestation respectively. In conclusion, the relationship between placenta thickness, gestational age and foetal weight has been established, sex differences exist in foetal growth parameters, there is no significant difference when foetal growth parameters were grouped according to parity, but level of education and ethnicity had significance on foetal growth parameters, some maternal parameters showed significant relationship with foetal growth parameters, while placenta thickness will be able to predict gestational age and foetal weight among Nigerian pregnant women.
TABLE OF CONTENTS
Cover Page …………………………………………………………………………………………………. i
Fly Leaf ……………………………………………………………………………………………………… ii
Title Page ……………………………………………………………………………………………………. iii
Declaration …………………………………………………………………………………………………. iv
Certification ………………………………………………………………………………………………… v
Acknowledgements ……………………………………………………………………………………… vi
Dedication ………………………………………………………………………………………………….. vii
Table of Contents ………………………………………………………………………………………… viii
List of Tables ………………………………………………………………………………………………. xi
List of Figures …………………………………………………………………………………………….. xii
List of Plates ……………………………………………………………………………………………….. xv
List of Appendices ………………………………………………………………………………………. xvi
Abstract …………………………………………………………………………………………………….. xvii
1.0 INTRODUCTION ………………………………………………………………………………… 1
1.1 Background of the Study ………………………………………………………………………. 1
1.2 Statement of Problem ……………………………………………………………………………. 5
1.3 Justification/Significance of the Study …………………………………………………… 5
1.4Aim and Objectives of the Study ……………………………………………………………. 6
1.4.1 Aim of the study ………………………………………………………………………………….. 6
1.4.2Objectives of the study ………………………………………………………………………….. 6
1.5 Study Hypotheses …………………………………………………………………………………. 7
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2.0 LITERATURE REVIEW ……………………………………………………………………… 8
2.1 Ultrasound ……………………………………………………………………………………………. 8
2.1.1 Basic physics ………………………………………………………………………………………. 8
2.1.2 Generation of ultrasound ………………………………………………………………………. 8
2.1.3 Ultrasound techniques …………………………………………………………………………. 9
2.1.4 Ultrasound in obstetrics and gynaecology ………………………………………………. 10
2.1.5 Application of ultrasound in obstetrics …………………………………………………… 11
2.2 Placenta ……………………………………………………………………………………………….. 27
2.2.1 Development of theplacenta ………………………………………………………………….. 27
2.2.2 Components of theplacenta …………………………………………………………………… 28
2.2.3 Structure of theplacenta ………………………………………………………………………… 28
2.2.4 Full termplacenta …………………………………………………………………………………. 29
2.2.5 Circulation of theplacenta …………………………………………………………………….. 30
2.2.6 Placental changes at the end of pregnancy ………………………………………………. 31
2.2.7 Functions of theplacenta ……………………………………………………………………….. 32
2.2.8 The placenta as an allograft …………………………………………………………………… 34
2.2.9 Ultrasound of theplacenta ……………………………………………………………………… 35
2.3 A Short History of Zaria Local Government Area, Kaduna State …………… 54 3.0 MATERIALS AND METHOD ……………………………………………………………… 57 3.1 Materials ……………………………………………………………………………………………… 57 3.2 Sample Population ………………………………………………………………………………… 65 3.3Data CollectionTechniques/Methodology ……………………………………………….. 65
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3.3.1Ultrasonographic parameters ………………………………………………………………….. 65
3.3.2 Maternal parameters …………………………………………………………………………….. 67
3.3.3 Inclusion and exclusion criteria ……………………………………………………………… 69
3.3.4 Study location ……………………………………………………………………………………… 70
3.4Ethical Consideration …………………………………………………………………………… 71
3.5 Statistical Analyses ……………………………………………………………………………….. 71
4.0 RESULTS …………………………………………………………………………………………….. 73
4.1Analyses of Study Population ………………………………………………………………… 73
4.2Anthropometric Variables and Foetal Parameters …………………………………. 73
4.3 Foetal Ultrasonographic Parameters …………………………………………………….. 89
4.4Foetal Growth Parameters According to Ethnic Group, Mothers Level
of Education, Parity and Sex of Foetus ……………………………………………………… 91
4.5Correlation Between Maternal Anthropometry and Foetal
Sonographic Parameters …………………………………………………………………………….. 109
4.6Predictive Equations of Placenta Thickness for Gestational Age and
Foetal Weight …………………………………………………………………………………………… 119
5.0 DISCUSSION ……………………………………………………………………………………… 127
6.0 CONCLUSION AND RECOMMENDATIONS …………………………………….. 135
6.1Conclusion …………………………………………………………………………………………….. 135
6.2Recommendations …………………………………………………………………………………. 136
6.3Contribution to Knowledge ……………………………………………………………………. 136
REFERENCES ………………………………………………………………………………………….. 138
APPENDICES …………………………………………………………………………………………… 156
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CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the Study
Placental dysfunction has been implicated in the development of a variety of commonly encountered obstetric complications (Schwartz et al., 2011; Holroydet al., 2012; Mathaiet al., 2013; Miwa et al., 2014). In fact, most reproductive biologists agree that many adverse pregnancy outcomes, such as preeclampsia, foetal growth restriction, and stillbirth, are often the result of abnormal trophoblastic invasion and placental implantation, which are largely completed by the end of the first trimester (Holroydet al., 2012; Miwa et al., 2014; Veerbeeket al., 2014). In fact, there is increasing evidence linking placental development to long-term health consequences in the offspring, even into adulthood (Barker et al., 2011; Eriksson et al., 2011; Misraet al., 2012; Ouyanget al., 2013; Ballaet al., 2014).
The in utero environment and its impact on neonatal health are of increasing interest in relation to adult health outcomes(Barker et al., 2013; Suriet al., 2013).There is a growing body of evidence that birth weight and placental insufficiency are important risk factors for later development of the so-called metabolic syndrome such as hypertension, diabetes, and coronary heart disease(Schwartz et al., 2011; Barker et al., 2013).The placenta is the principal influence on foetal birth weight, and it is thought that abnormalities of placental growth may precede abnormalities in fetal growth (Afrakhtehet al., 2013; Miwa et al., 2014).Studies have shown that diminished placental size precedes foetal growth retardation as intrauterine growth restriction (IUGR) isassociated with impoverished villous development and fetoplacental angiogenesis (Joneset al., 2013; Morganet al., 2013).
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Placenta is a foetal organ with important metabolic, endocrine and immunological functions and provides the physiological link between a pregnant woman and the foetus. The placenta is the primary site of nutrient and gas exchange between the mother and embryo/foetus.The placenta develops from chorionic villi at the implantation site at about the fifth week of gestation and by the tenth week the granular echotexture of placenta is apparent on ultrasonography (Sadler, 2012; Gasser et al., 2014; Moore et al., 2016).Historically, a placenta of greater than 4 cm in thickness has been regarded as abnormal (Hoddicket al., 1985) and associated with various poor outcomes (Dombrowski et al., 1992; Miwa et al., 2014).
Because the placenta may be the first organ to manifest changes of disease in pregnancy, placental features may have a role in screening for pregnancy complications (Lee et al., 2012; Warranderet al., 2012; Miwa et al., 2014).Thick placenta is associated with maternal diabetes mellitus, foetal hydrops and intrauterine foetal infections and adverse clinical outcome (Elchalalet al., 2000; Raioet al., 2004; Miwa et al., 2014). Perinatal morbidity and neonatal conditions were worse in cases with thick placenta rather than without thick placenta (Raioet al., 2004; Karthikeyan et al., 2012; Miwa et al., 2014).
Sonography has provided a safe and non-invasive means to evaluate the placenta. Its size and growth pattern have a bearing on foetal outcome (Holroydet al., 2012; Afrakhtehet al., 2013; Kaushal et al., 2015). Placental thickness (PT) also helps in differentiating normal from abnormal pregnancy (Suriet al., 2013; Ptaceket al., 2014). Small and thin placenta is associated with intrauterine growth retardation of the foetus(Longtineand Neslson, 2011; Veerbeeket al., 2014).
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The gestational age (GA) is of utmost importance in providing the best possible ante partum care andsuccessful deliveries of babies (Chudleigh and Thilaganathan, 2004; Sanders and Winter, 2012; Yee and Grobman, 2016). Virtually, all theimportant clinical decisions, which include caesarean section, elective labour induction, etc, depend on the knowledge of the gestational age (Sanders and Winter, 2012; Yee and Grobman, 2016).Ultrasonography (USG) is commonly used to estimate the gestational age by measuring foetal dimensions like the biparietal diameter (BPD), abdominal circumference (AC), head circumference (HC) and the femur length (FL) (Hadlock et al., 1984; Chudleigh and Thilaganathan, 2004; Sanders and Winter, 2012; Khambaliaet al., 2013).
Placental thickness is the easiest placental dimension to measure, yet little is known about the ―normal‖ PT as measured by sonography. Also, placental thickness appears to be a promising parameter for estimation of gestational age of the foetus because of increase in placental thickness with gestational age (Mathai et al., 2013; Nagwaniet al., 2014; Adhikariet al., 2015). Studies by some authors have reported the use of placental thickness as an indicator of gestational age (Jainet al., 2001; Tiwari and Chandnani, 2013; Ahmed et al., 2014;Kapoor and Dudhat, 2016).Currently, the routine prenatal sonographic examination includes only a limited and qualitative assessment ofthe in utero placenta, with no quantitative method to evaluateplacental growth and development (AIUM, 2013; ACOG, 2014).
In fact, there is evidence that placental thickness may vary with the implantation site and that anterior placentas tend to be thinner than posterior placentas (Lee et al., 2012; Ali et al., 2013), casting further doubt on the relevance of a categorical 4-cm cutoff. An Israeli prospective cross-sectional study (Elchalalet al., 2000) found a linear increase in
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placental thickness with gestational age throughout pregnancy. That study also suggested a correlation between an abnormally thick placenta (defined as >90th percentile) and a poor outcome in terms of perinatal mortality and growth restriction (Elchalalet al., 2000).Studies over time have shown that the maternal ethnic group impacts not only the foetal weight, but also influences placental weight, volume and surface of implantation(Freeman et al., 1970; Jackson et al., 1987; Zhan, 1989; Sivaraoet al., 2002; Gomes et al., 2005; Ouyanget al., 2013; Ballaet al., 2014).AlsoOhagwu and his colleagues demonstrated a placental thickness of about 4.5 cm for a normal Nigerian pregnant woman(Ohagwuet al., 2009).
Thick placentas have been associated with various maternal and foetal conditions, including toxoplasmosis, rubella, cytomegalovirus, herpes simplex virus, and other infections(TORCH infections), diabetes, and hydrops (Hoddicket al., 1985; Miwa et al., 2014). Small placentas have also been associated with perinatal complications. In a prospective study involving 712 women, Thameet al showed that a low birth weight was often preceded by small placental volumes in the second trimester (Thameet al., 2001). Similarly, Hafner‘s group (Hafner et al., 2003) determined that small for gestational age placentas were already significantly smaller than the placentas of non–small for gestational age foetuses at 12 weeks, indicating that placental growth is already reduced in these foetuses in the first trimester.
Despite these studies, the clinical importance of abnormally large or small placentas remains unclear (Hoddicket al., 1985; Hafner et al., 2003; Lee et al., 2012). PT is the easiest placental measurement to obtain and could therefore play a potential role in screening for complications during routine ante natal sonography, (Habib, 2002; Hafner et al., 2003; Lee et al., 2012; Miwa et al., 2014) while also being able to estimate fetal
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weight and gestational age (Afrakhtehet al., 2013; Suriet al., 2013; Tiwari and Chandnani, 2013; Baghelet al., 2015).
1.2 Statement of theResearch Problem
Routine sonographic prenatal evaluation lays most emphasis on the quality and ignores the impact of the quantitative aspect of placental morphology. Sonographic research data and awarenessare scarce in Nigeria in particular and the African continent in general and even where available have not been properly harnessed for its medical and research purposes. The base value of placenta thickness is 4 cm reported more than 25 years ago in a study conducted among Caucasians. A study conducted in Nigeria was able to show that a normal PT could be up to 4.5 cm. Also, nowhere in the literature to best of our knowledge has the relationship between maternal anthropometry and foetal sonographic growth parameters been investigated. This current study will increase the sample size, investigate the sexual dimorphism of PT for a more generalization of our findings, investigate the effect of ethnicity on PTand foetalsonographic characteristics, the possibility of using PT to predict foetal weight and gestational age, while the relationship between maternal anthropometry and foetalsonographic characteristics will also be investigated.
1.3 Justification of the Study
PT is the easiest placental dimension to measure yet little is known about the normal thickness among Nigerian pregnant women. The possibility of using the PT as a means of dating foetusesand the ethnic variation in placental thickness measured sonographically has never been explored anywhere in the literature to the best of our
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knowledge. Even though a normal placenta thickness of 4 cm has been established over 25 years ago, the effect of an abnormally thick placenta on foetal parameters remains clinically unclear. It will also be the first study to investigate the relationship between maternal anthropometry and foetal sonographic growth characteristics.
The results of this study will enlighten clinicians, scientists and healthcare providers on using PT measured sonographically as a means of assessing foetal health and predicting gestational age. This study will also provide a reference value for PT among Nigerian pregnant women. Finally, this study will add to the scanty literature available on sonographic research in Nigeria and Africa in general.
1.4Aimand Objectivesof the Study
1.4.1 Aim of the study
The aim of the present study was to determine placental thickness according to sex and its relationship to other foetal characteristics in second and third trimesters using ultrasonography.
1.4.2 Objectives of the study
This study was designed with the following objectives:
i. investigate the sex differences in biparietal diameter (BPD), head circumference (HC), occipitofrontal diameter (OFD), femoral length (FL), abdominal circumference (AC) and placental thickness (PT) in male and female foetuses.
ii. determine PT across trimesters in Nigerian pregnant women.
iii. investigate the relationship between PT, foetal weight and gestational age.
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iv. assess the possibility of using the PT as a means of dating foetuses and correlating PT with gestational age.
v. use PT measurement to correlate with other standard dating parameters like FL, BPD, HC and AC.
vi. use PT to predict FL, BPD, HC, AC, foetal weight and FHR.
vii. investigate the effect of ethnicity on foetal characteristics obtained by ultrasonography.
viii. investigate the relationship between maternal anthropometry and foetal sonographic growth parameters.
1.5StudyHypotheses
The study was conducted with the following hypotheses in mind:
i. placenta thickness will correlate with foetal characteristics such as FL, BPD, HC and AC and predict gestational age (GA) and fetal weight (FW).
ii. maternal characteristics such as age, weight, and heightwill have no relationship with placenta thickness and PT will be less than 4 cm in the study population.
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