ABSTRACT
Ultrasonographic foetal biometry has proven to be a reliable
tool in the correct estimation of gestational age and assessment of foetal
growth. The choice of a reference chart is critical to the proper assessment of
foetal biometry due to observed racial differences. Therefore this study was
designed to establish foetal biometric standards in Ghanaians. A prospective, cross-sectional
study was conducted using a total of 374 pregnant women with known last
menstrual period from the Sunyani Municipal Hospital and the Suntreso
Government Hospital from October 2015 to March 2016. Measurements of crown-rump
length, biparietal diameter, head circumference, abdominal circumference and
femur length were obtained via transabdominal sonography. Results of the
present study provide for the first time detailed baseline data on foetal
biometry in Ghana and show that there is significant disparity between
gestational age estimated by the last menstrual period and ultrasound. Head
circumference was the best parameter in estimating gestational age in the
second and third trimesters of pregnancy with coefficient of determination (R2)
of 96.6% and 84.1% respectively. Combinations of head circumference or
biparietal diameter, abdominal circumference and femur length in the third
trimester increased the R2 to 90 or 90.5%. Biparietal diameter was a
good predictor of gestational age in the third trimester than previously
reported in the literature suggesting normal cephalic indices in the present
population. Statistically significant differences in foetal biometry exist
between the present population and the American, British and Chinese populations
in the literature. This study provides preliminary baseline data for the
estimation of gestational age and assessment of foetal growth by sonographers
and obstetricians.
CHAPTER ONE
INTRODUCTION
The estimation of gestational age and the assessment of size
and growth of the embryo or foetus are routinely performed during antenatal
care (Butt and Lim, 2014). Gestational age is the age of pregnancy (Kalish and
Chervenak, 2005). Knowing how long the embryo or foetus is in utero is
important in predicting the expected date of delivery and hence proper
classification of term, preterm and postterm dates (Blondel et al., 2002).
Determination of antimalarial drug regime (Rijken et al., 2012) and the scheduling
of initiation date for Zidovudine treatment (Traisathit et al., 2006) depend on
knowledge of the gestational age. Accurate dating is also paramount to the
proper timing of foetal genetic screening (nuchal translucency, chorionic villi
sampling and amniocentesis), testing for foetal lung maturity as well as
relating the various maternal blood serum (pregnancy-associated plasma
protein-A, alpha-fetoprotein, human chorionic gonadotropin, estriol and
inhibin-A) levels to risk factors (Kalish and Chervenak, 2005; Neufeld et al.,
2006). Virtually all important clinical decisions in obstetrics are dependent
on accurate estimation of gestational age (Merritt et al., 1992).
Traditionally the gestational age is estimated from the first
day of the last menstrual period (LMP) since the day of conception cannot be
accurately known (MacGregor and Sabbagha, 2008; Whitworth et al., 2015). The
reliability of LMP-based gestational age estimation however depends on the
regularity of a woman’s menstrual cycle, accurate recall of LMP, interpretation
of bleeding in early pregnancy, lactational amenorrhoea, contraceptives use
prior to pregnancy and variations in the timing of ovulation and fertilization
(Geirsson, 1991; Nguyen et al., 2000; Salpou et al., 2008). About 11 – 42% of
gestational age estimated by LMP are reported as inaccurate (Nguyen et al., 2000; Whitworth et
al., 2015). The symphysis-fundal height (SFH) measurement is also used as a
proxy in estimating gestational age and assessing growth abnormalities (foetal
growth restriction and macrosomia) (Ogbe et al., 2015; Robert et al., 2015).
The detection rates of small-for-gestational-age babies using SFH ranges from
56% - 86% (Robert et al., 2015). The SFH measurement is affected by the
technique used, the number of clinicians involved, multiple pregnancies, status
of the maternal bladder, maternal position, pre-pregnant weight, molar
pregnancy, amniotic fluid level, macrosomia and intrauterine growth restriction
(Engstrom et al., 1993; Steingrímsdottir et al., 1995).
In recent years foetal biometry through the use of ultrasound
has become indispensable tool for the practice of obstetrics. Ultrasonography
is safe, non-invasive, accurate and cost-effective than other diagnostic
imaging modalities (Rueda et al., 2014). Ultrasonographic foetal biometry is
the measurements of various structures of the foetal anatomy (Shehzad et al.,
2006). Ultrasonography has proven to be the best method for estimating
gestational age and the expected due date (Salomon et al., 2011; Butt and Lim,
2014). This has reduced expensive hospitalization and unnecessary interventions
such as induction of labour and tocolytic treatments due to wrongfully assumed
foetal growth abnormality, preterm and post-term labour (Pemberton et al.,
2010; Brakohiapa et al., 2012). Ultrasonographic foetal biometry is more useful
in estimating foetal weight and diagnosing intrauterine growth restriction
(IUGR) and macrosomia than abdominal palpation and symphysis-fundal height
(Salomon et al., 2011; Butt and Lim, 2014).
There are two approaches in the study of foetal biometry: a
cross-sectional study and a longitudinal study (Loughna et al., 2009). In a
cross-sectional study, a foetus is measured only once during gestation.
It is appropriate for creating foetal size and age charts. Foetal size charts
and foetal age charts are not synonymous (Briceño et al., 2013). In foetal size
chart, the foetal parameter is plotted as a function of gestational age whereas
in foetal age chart, the gestational age is plotted as a function of the foetal
parameter (Loughna et al., 2009). Longitudinal study involves serial
measurements of the same foetus for at least three times during pregnancy. It
is best used in creating foetal growth charts (Loughna et al., 2009).
Various foetal biometric parameters have been sonographically
measured for the creation of foetal age, size and growth charts (Shehzad et al.,
2006). They include measurements of mean gestational sac diameter, transverse
cerebellar diameter, liver length, kidney length, intra/interorbital diameters,
clavicular length, humeral length, scapula length, sacral length and nasal bone
length (Shehzad et al., 2006; Butt and Lim, 2014). The commonly measured
parameters, sometimes referred to as the gold standard of foetal biometric
measurements, are the crown-rump length (CRL), biparietal diameter (BPD), head
circumference (HC), femur diaphysis length (FL) and abdominal circumference
(AC) (Shehzad et al., 2006). Many clinical decisions depend upon accurate and
reproducible measurements of foetal biometry and choice of appropriate
reference charts.
1.1 THE PRESENT
STUDY
Maternal mortality is unacceptably high across the developing
countries, including Ghana. The maternal mortality ratio in 2015 for Ghana was
319 per 100,000 live births and the neonatal mortality in 2013 was 29 per 1,000
live births (UNICEF, 2015). In order to achieve the United Nations Sustainable
Development Goals (SDGs) 3.1 and 3.2 of reducing the global
maternal mortality ratio to less than 70 per 100,000 live births and neonatal
mortality to at least as low as 12 per 1,000 live births by 2030 (UN, 2015)
respectively, the role of obstetric ultrasonography cannot be underestimated.
An appropriate reference table for ultrasound dating and a reliable reference
foetal size chart can improve obstetric management in pregnancy and hence
reduce perinatal mortality and morbidity (Lausman et al., 2013; Pay et al.,
2015)
Ultrasonographic foetal biometry assumes that the size of an
embryo or a foetus is consistent with its age (Butt and Lim, 2014). Different
embryos or foetuses of the same biometric measurements can have different
gestational ages. Alternatively, different embryos or foetuses of the same
gestational age can have the same or different biometric measurements. This
indeed is a clinical dilemma since this may suggest normal foetal growth,
intrauterine growth restriction (small-for-gestational-age) or macrosomia
(large-for-gestational-age). The state of the embryo or foetus can be
ascertained by comparing the size or age as the case may be with a reference
chart of a specific population derived from low-risk pregnancies. Several
reference age and size charts of foetal biometric parameters have been
published for populations in Europe (Chitty et al., 1994 a, b, c; Snijders and
Nicolaides, 1994; Kurmanavicius et al., 1999 a, b; Paladini et al., 2005;
Salomon et al., 2006), America (Deter et al. 1982; Hadlock et al., 1982 a, b,
c, d), Asia (Lachman and Shen, 1996; Salomon et al., 2006; Jung et al., 2007)
and Africa (Okonofua et al., 1988; Salpou et al., 2008; Mador et al., 2011).
These tables and equations have been included in most ultrasound software
programme for obstetric use. Since the charts and tables are many, the choice
of a reference chart is important in the assessment of foetal biometry (Salomon
et al., 2005). An inappropriate reference chart can pose significant clinical
implications since this may mislead the obstetrician as to the true state of
health or development of the foetus. Using Z-scores, Salomon et
al. (2005) observed that the number of foetuses that would have been considered
abnormal (below 5th centile and above 95th centile) based on the references by
Snijders and Nicolaides (1994), Chitty et al. (1994a, b, c) and Kurmanavicius et
al. (1999a, b) to the French population ranged from 2.6% to 23.6% for BPD, HC
and FL. The specificity and sensitivity ranged from 90.1% to 99.7% and 39.6% to 67.1% respectively. None of the references
for AC was found to be acceptable to the French population.
Differences in foetal biometry have been attributed to race
or ethnicity, maternal age, parity, nutritional status and foetal sex (Davis et
al., 1993; Jacquemyn et al., 2000; Leung et al., 2008). Even within a
population, Krampl et al. (2000) found that geographical changes such as
altitude affect foetal size. These have prompted many researchers (Hadlock et
al., 1982a, b, c, d, e; Chitty et al., 1994a, b,c; Leung et al., 2008;
Westerway et al., 2000; Buscicchio et al., 2008) to develop reference charts
that are specific to their populations. Hadlock and coworkers’ charts (Hadlock et
al., 1982a, b, c, d, e; Hadlock et al., 1984a) that are commonly used in Ghana
were developed over 30 years ago from middle class Caucasian women, which are
not representative of the Ghanaian population. Also, reference charts over 30
years old were developed using obsolete ultrasound equipment, suboptimal study
designs and statistical analyses (Altman and Chitty, 1994). Some researchers
(Westerway et al., 2000; Buscicchio et al., 2008) have even called for the
revision of older foetal nomograms due to increasing in birthweights in the
last decades (Irgens, 2000).
Cross-sectional reference foetal charts and equations from
the Ghanaian population using appropriate methods have not previously been
published in the literature. Also, there are no standard reference tables and
charts for foetal size and foetal age assessment and a number of ultrasound
centres are unable to clarify the reference charts and tables they are using.
The choice of reference charts have often being based on preference or on the
chart that is loaded by default in the software of the ultrasound machine. The
present study attempts to establish reference baseline charts and tables in the
Ghanaian population for standard foetal biometric parameters using the methods
recommended by Altman and Chitty (1994) and Royston and Wright (1998).
1.2 AIM AND
OBJECTIVES
1.2.1 AIM
To establish the need for foetal biometric standards for
Ghanaians.
1.2.2 OBJECTIVES
* To determine menstrual-based gestational age and
ultrasound-based gestational age.
* To determine the degree of discrepancy between
ultrasound-based gestational age and menstrual-based gestational age.
* To establish reference charts for foetal age and size
estimation based on sonographic measurements of crown-rump length, biparietal
diameter, head circumference, abdominal circumference, femur length and their
ratios.
* To compare the foetal size and age charts in the present
study with published charts.
* To determine the best parameter (s) in estimating gestational
age in the second and third trimesters of pregnancy.
For more Anatomy Projects Click here
===================================================================
Item Type: Ghanaian Topic | Size: 197 pages | Chapters: 1-5
Format: MS Word | Delivery: Within 30Mins.
===================================================================
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.