Estimation of Fetal Size and Weight using Various Formulas

Copyright © 2019 by author(s) and International Journal of Trend in Scientific Research and Development Journal. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0) (http://creativecommons.org/licenses/ by/4.0) ABSTRACT Birth weight is an important factor in delivery management. Antenatal ultrasound has turned out to be one of the clinicians' most vital devices for surveying fetal age, growth and prosperity. Contrasted Physical examination of the pregnant uterus is the most precise strategy for evaluating fetal size and growth along with the utilization of ultrasound imaging and estimating of the different fetal parameters. Objective: To evaluates the antenatal assessments of fetal weight in pregnancies by using Johnson’s formula, Hadlock’s formula and Ultrasonography. Comparison of these different methods with the actual birth weight of these babies after delivered. Material and methods: Two hundred singleton term pregnancies within 48 hours were randomly selected to participate in this prospective cohort study. Variables included such as abdominal circumference, Biparietal diameter, and Femur length. (Parameters to obtain estimated fetal weight) Results: The mean birth weight of Hadlock formula is closest to the mean of actual birth weight. In the study population, more primigravida delivered babies with very low birth weight and more multigravida delivered babies of birth weight > 3500 gms. Johnson’s and ultrasound-Hadlock’s formula had a marked tendency to overestimate the fetal weight. Error was within 350 Gms in 84.7%, 70.8% and 84% of cases by Dare’s, Johnson’s and ultrasound-Hadlock’s formula.


Introduction:
Making posterity is one of women most regarded accomplishments and delights. Over a large portion of a million women around the globe pass on amid pregnancy and childbirth (WHO, 2004). "Information of fetal size has two fundamental applications in obstetric practice. The first is to look at the size of an embryo of obscure gestational age with ordinary figures and so acquire a gauge of the development of the hatchling. The second application is to look at the size of an embryo of known gestational age with referred to ordinary either as a solitary perusing to tell whether the hatchling being referred to is bigger or littler than typical or, better, as a progression of readings. Ultrasonography imaging has emerged as the primary imaging modality for assessing the obstetric patient. Over the years, various radiologic imaging modalities have been used in pregnant women, but none can match the benefits of Ultrasonography; a relatively low-cost, real time imaging modality that doesn't involve ionizing radiation. There are two reliable EFW formulas, both giving low deviations from actual birth weight and with low error of 7.7 and 7.9% across the weight ranges. (Had lock group formula B with parameters and the Had lock formula C with parameters) For all formula the highest random error occurred in the macrosomic group. The lowest random error in all weight groups was the Had lock B formula incorporating the HC/AC/FL (7.7%). (Susan Campbell Westerway, 2012).A study by Esinler et al 2015, enrolled participants 495, calculated the fetal weight using 18 different formulas. The mean percentage error, the mean absolute percentage error and reliability analysis were used to compare the performance of the formula. This study concluded that Had lock I, Had lock's III and Ott may be used to predict the estimated fetal weight accurately in all fetuses in their study. Formula Ott, Had lock's IV and Coombs may be preferred to predict the fetal weight in fetuses <2,500 g, and >4,000 g. Better formulas should be developed to predict the fetal weight in fetuses >4,000 g. To describe the assessment of fetal weight using different formula with parameters (with the sample error), this study was undertaken.

Materials and Methods:
This study was a prospective cohort study approved by ethics committee of the Maternity Hospital Southern region of Tamilnadu. Two hundred pregnant women admitted at full term for planned delivery either by elective caesarean section or by induction of labor. Mothers with live singleton fetus who had their gestational age confirmed by dates and ultrasound done before 22 weeks. All measurements will be taken within one week of delivery. If undelivered beyond this time interval the measurements will be repeated within 48 hours. Therefore Multiple gestations, Patient with polyhydraminos or oligohydramnios., Abnormal lie, Preterm labor, Fetal malformations, Antepartum hemorrhage, Eclampsia, Obese patients (>90kg), Uterine / ovarian mass complicating pregnancy were excluded.
Data Collection: Real time ultrasound scan, equipment Philip HD 7 was used to measure abdominal circumference (AC), Biparietal diameter (BPD), Head Circumference (HC), and femur length (FL). Consent: Prior to allocation, participants were counseled regarding the study, and explained that ultrasound which is a routine for obstetrics cases is a non-invasive and safe procedure. Consent was obtained in a designated form.
Research questions: was with regard to a. What would be the accuracy of antenatal assessment of fetal weight in pregnancies by using Johnson's formula, Had lock formula and Ultrasonography? B. Comparison of these different methods with the actual birth weight of these babies after delivery.
Statistical Analysis: After completion of the study, continuous data were analyzed and presented as mean ± standard deviation, and categorical variables were presented as count and percentage.

Discussion:
The mean simple error is least in Dare method than USG but when correlation coefficient was calculated in different methods, it was evident that USG seems to be correlating well with actual birth weight than Dare's and Johnson's methods which seems to be least correlated and this correlation was statistically significant. After applying wilcoxon rank sum test to the mean absolute percentage error of Dare's formula and ultrasound methods, the difference among the mean absolute percentage errors of these two methods were statistically significant. Hence antenatal assessment of the birth weight of the babies is more accurate with USG method followed by clinical estimation of the birth weight by Dare's formula. When compared with normal birth weight babies estimated within the 10% of actual birth weight by different methods with large for gestational age babies from the above Clinical estimation of birth weight may be as accurate as routine ultrasonography estimation, except in low-birthweight babies. From our study, it can be concluded that antenatal fetal weight can be estimated with considerable accuracy by abdominal girth, symphysio-fundal height and ultrasound Had lock's formula. Abdominal girth, symphysiofundal height is simple, inexpensive and of immense value in developing country like ours, hence it can be used anywhere even by domiciliary midwives to predict fetal weight. Accuracy of Johnson's formula was less than abdominal girth x symphysio-fundal height and ultrasound -Had lock's formula.