Estimating foetal weight by Johnson's formula, your own experienced fingers or USG:- Choice is yours!!
Is
sonographic estimates of foetal weight (EFW)
superior to clinical estimations of foetal weight as used be done in the
decades of forties to eighties (pre USG Era) ?
If
you are not strong in Math(like me) then
don’t go for 12 other formulae described below for calculation of foetal weight
stick to A) your palpating fingers, B) USG
and C) if USG machine is out of order /unaffordable then go ahead for Jonson’s formula for
calculation of EFW .
.But if U are very strong in Maths then you can use any of the other 12 other formulae
which I am enclosing for prediction of foetal weight,. Choice is
yours!!
Q.1. why clinical estimation of foetal weight
is still relevant?? Ans; A long que in
Radilogy deppt and in some hospitals there is no in house wee USG at Ante OPD . Load of antental mothers !!! According
to estimates
Population change rates in 2020
According to our
estimations, daily change rates of India population in 2020 will be the
following:
- 77,575 live births average per day
(3,232 in an hour)
- 28,164 deaths average per day
(1,173. in an hour)
- -1,558 emigrants average per day
(-64.93 in an hour)
28,164 deaths average
per day (1,173) in
an hour)-Precovid era . Can Radio daig people manage such
work load in addition to cases refd from Medicine, surgery wings??
Q.1;
Where large baby?? Management of diabetic pregnancy, vaginal birth after a
previous caesarean section, and intrapartum management of foetuses presenting
by the breech will be greatly influenced by estimated foetal weight .Also, when
dealing with anticipated preterm delivery, perinatal counseling on likelihood
of survival, the intervention undertaken to postpone preterm delivery, optimal
route of delivery, or the level of hospital where delivery should occur may be
based wholly or in part on the estimation of expected birthweight.
Categorization of foetal weight into either small or large for gestational age may lead to timed
obstetric interventions that collectively represent significant
departure from routine antenatal care.
Dangers of LBW? A large portion
of neonatal; survival is
related to birthweight which remains the single most important parameter that
determines neonatal survival .It is estimated that 16% of live born infants
have low birthweight, a condition associated with high perinatal morbidity and
mortality.
Secondly,
foetal macrosomia is
associated with maternal morbidity, shoulder dystocia, birth asphyxia, and
birth trauma.
The two main methods for predicting
birthweight in current obstetrics are: (a) clinical techniques based on
abdominal palpation of foetal parts and calculations based on fundal height and
(b) sonographic measures of skeletal foetal parts which are then inserted into
regression equations to derive estimated foetal weight .
Q.2: Which one is superior-clinical
or sonological ?? Although some investigators
consider sonographic estimates to be superior to clinical estimates, others, in
comparing both the techniques concurrently, conclude that they confer similar
levels of accuracy.
The
available techniques can be broadly classified as: (a) clinical methods:
A)By using Leopold's manoeuvre: a tactile assessment of foetal size, e.g.;
clinical risk factor; maternal self-estimated foetal weight;
B)
Jonson’s formula and prediction of equations of birthweight and (c)
imaging methods: ultrasonography and magnetic resonance imaging.
Tactile
assessment of foetal size: . It
is the oldest technique for assessing foetal weight through manual assessment
of foetal size by obstetricians worldwide, i.e. by external palpation of the
uterus and foetal parts. This method is extensively used because, knowingly or unknowingly
we , a; of s do it in day to day practice. This is both convenient and
virtually costless. However, it has long been known as a subjective method that
is associated with significant
predictive errors. It is both patient- and clinician-dependent for its
success (less accurate for obese gravidas than non-obese and significant
inter-observer variation in prediction of birthweight even among experienced
clinicians) .
Clinical
risk factor: This involves quantitative
assessment of clinical risk factors and has been shown to be valuable in
predicting foetal weight.
In the case of foetal macrosomia, the presence
of risk factors, such as maternal diabetes mellitus, abnormal glucose screening
test, prolonged pregnancy, 1) maternal
obesity, 2) pregnancy-weight gain of >20 kg, 3) maternal age of >35
years, 4) maternal height >5 ft 3 in,5) multiparity, 6) male foetal sex, and 7) white
race, should make the obstetrician suspicious of foetal macrosomia and assess
accordingly.
Maternal self-estimation: Perhaps surprisingly in developed (literate) society,
maternal self-estimation of foetal weight in multiparous women shows comparable
accuracy to clinical palpation in some studies for predicting abnormally large
foetuses (Source:- . Benacerraf BR, Gelman R, Frigoletto FD., Jr
Sonographically estimated fetal weight: accuracy and limitation. Am J
Obstet Gynecol. 1988;159:1118–. and Chauhan SP, Lutton PM,
Bailey KJ, Guerrieri JP, Morrison JC. Intrapartum clinical, sonographic, and
parous patients’ estimates of newborn birth weight. Obstet
Gynecol. 1992;79:956–8.
The
third method :-Birth-weight prediction
equations: There are been many formulae
for calculation of foetal weight by using few maternal biometric variables
which sometimes confuse us , But out of so many formulae Jonson’s formula is commonly used.
a)
Various other calculations and
formulae based on measuring uterine fundal height above symphysis pubis have
been developed.like Ojwang et al who used the product of
symphysiofundal height and abdominal girth measurement at various levels in
centimetres above the symphysis pubis in obtaining a fairly acceptable
predictive value but with considerable variation from the mean(ref:- Ojwang S,
Ouko BC. Prediction of fetal weight in utero by fundal height/girth
measurements. J Obstet Gynecol East Central Afr. 1984;3:111. [Google Scholar]
b)
Dare et al. in
OAUTHC, Ile-Ife, in 1988, used the product of symphysiofundal height and
abdominal girth at the level of the umbilicus measured in centimetres and
result expressed in Gm to estimate foetal weight at term in-utero, and the
estimate correlated well with birthweight( Dare FO, Ademowore AS, Ifaturoti OO, Nganwuchu
A. The value of symphysiofundal height/abdominal girth measurement in
predicting fetal weight. Int J Gynaecol Obstet. 1990;31:243–8)
Johnson's
formula for estimation of foetal weight in vertex presentation is as follows: Foetal weight (g)=fH
(cm)n × 155.
fH=fundal height in cm and n=12 if vertex is
above ischial spine ) It will be n= 11 if vertex is below ischial spine.
·
If a patient weighs more than 91 kg, 1 cm is.
c)
11 if vertex is below ischial spine. If a patient weighs more
than 91 kg, 1 cm is subtracted from the fundal height.
Foetal
weight (g)=fH (cm)n × 155. fH(Fundal Ht in cm) =fundal height and n=12
But
if vertex is above ischial spine But “n”
will be 11 if vertex is below ischial
spine. If a patient weighs more than 91 kg, 1 cm is subtracted from the fundal
height.
Learn higher mathematics:--Predicting foetal weight using
algorithm derived from maternal and pregnancy-specific characteristics. Recently, a new theoretically-defensible equation that
can predict individual birthweight prospectively from maternal characteristics
was developed. To do this, the efficacy of 59 scientifically-justifiable terms
was evaluated simultaneously, obviating any confounding co-variation and
determining which of the predictions could account for variation in birthweight
that others could not. Aside from maternal race, only six maternal and
pregnancy-specific variables were important in prediction of birthweight for
otherwise normal Gravidas.
Using
these routinely-recorded variables, an equation, based on maternal demographic
and pregnancy-related characteristics alone, was developed to help predict
birthweight as follows:
Birth-weight
(g)=gestational age (d) × [9.36 + 0.262 × foetal sex + 0.000237 × maternal
height (cm) × maternal weight at 26 weeks (kg) + (4.81 × maternal weight gain
rate (kg/d) × (parity+1)], where foetal sex is equal to +1 for male, -1 for
female, and 0 for unknown sex, and gestational age is equal to days since onset
of last normal menses which equals the conception age (d)+14). (source :- Nahum
G. Estimation of fetal weight—a review article last updated on 11 July
2002. ( http://www.emedicine.com, accessed on 28 March
2003). [Google Scholar]
Obstetric
ultrasonography. A modern method for assessing
foetal weight involves the use of foetal measurement obtained via ultrasonography.
The advantage of this technique is that it relies on linear and/or planar
measurement of in-utero foetal dimensions that are definable objectively and
should be reproducible. Early expectation that this method might provide an
objective standard for identifying foetuses of abnormal size for gestational
age was recently undermined by prospective studies that showed sonographic
estimates of foetal weight to be no better than clinical palpation for
predicting foetal weight .
Today,
sonographic predictions are based on algorithms using various combinations of
foetal parameters, such as abdominal circumference (AC), Femur length (FL),
biparital diameter (BPD), and head circumference (HC) both singly and in combination
as shown below
|
Like to learn higher mathematuics &
staistics: Hete is 12 formulae theat peope used earlier .Shepard |
1983 |
Log10BW=1.7492+0.0166(BPD+)
+ 0.0046(AC) - 0.00002646 (ACx BPD) |
|
Campbell |
1975 |
LnBW=4.564+0.0282
(AC)-0.0000331(AC)2 |
|
Hadlock
I |
1985 |
Log10BW=1.326–0.0000326
(ACxFL) × 0.00107(HC) + 0.00438 (AC) + 0.0158(FL) |
|
Hadlock
2 |
1985 |
Log10BW=1.304+0.005251(AC)
+ 0.01938 (FL) 0.00004(Acx FL) |
|
Hadlock
3 |
1985 |
Log10BW=1.335–0.000034(ACxFL)+0.00316x
(BPD)+0.0045 (AC)+0.01623 (FL) |
|
Warsof
1 |
1986 |
LnBW=4.6914+0.00151(FL)2-
0.0000119 (FL)3 |
|
Warsof
2 |
1986 |
LnBW=2.792+0.108
(FL)+0.000036 (AC)2-0.00027 (FLXAC) |
|
Combs |
1993 |
BW=(0.00023718x(AC)2x(FL)2)+0.00003312(HC)3 |
|
Ott |
1986 |
Log10BW=0.004355(HC)+0.005394
(AC)-0.00008582 (HCx AC)+1.2594 (FL/AC)-2.0661 |
|
Nzeh et
al. (formula1) |
1992 |
Log10BW=0.470+0.488
Log10BPD+0.554 Log10 FL+1.377 Log10AC |
|
Nzeh et
al. (formula 2) |
1992 |
Log10 BW=0.326+0.00451(SDI)+0.383
Log10BPD+0.614 Log10FL+1.485Log10AC |
|
Deter |
1985 |
EFW=101.335–0.0034AcxFL+0.0316BPD
+0.0457AC+0.1623FL |
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