Maternal and infant mortality is a major public health issue globally and in Uganda. In 2017, an estimated 295,000 women died during and following pregnancy and child birth, as a vast majority of these deaths (94%) occurred in low resource setting. Sub-Saharan Africa alone accounted for approximately two-third (196,000) of maternal deaths and 6.000 of these cases were from Uganda (1).
Antenatal care reduces both maternal and infant morbidity and mortality and prenatal fetal weight estimation is known to be an important component of standard antenatal care. Fetal weight is one of the determinants of outcome of pregnancies and is also the major determinant of infants’ wellbeing in the first year of life(2). Maternal risks associated with the delivery of an excessively big fetus include birth canal and pelvic floor injuries, as well as postpartum hemorrhage(3).
Accurate prediction of fetal weight is useful in the management of labor and reduces complications associated with macrosomia, thereby reduces maternal and peri-natal morbidity and mortality(4). Ultrasound is widely used preferentially over the clinical models of fetal weight estimation prenatally and excludes fetal anomalies among preterm fetuses(5). Although sonographic fetal weight could be predicted on single fetal parameter such as, the Biparietal Diameter (BPD), Abdominal Circumference (AC), Femur Length (FL), Head Circumference (HC) and Gestational age, a combination of several fetal parameters yields more accurate estimates of fetal weights(6, 7).
Fetal weight is influenced by several factors including maternal characteristics (age and weight), fetus related (anteriorly located placentae, oligohydramnios) and racial factors. Racial variation is an important factor to consider when sonographic fetal weight prediction models derived from one ethnic population are being used. All ultrasound scanners in Africa are imported from countries like America, Europe and Asia whose weight models are based on their population(8, 9). Most fetal weight formulae are based on the normal fetal growth curves and do not take into consideration the factors attributing to either a growth restricted or macrosomic (> 4000 g) fetus. Thus, the accuracy of fetal weight estimations, in predicting microsomic and macrosomic fetuses using fetal growth curves has been questioned(10, 11).
Obstetric sonographic assessment for the purpose of obtaining fetal biometric measurement to predict fetal weight has been integrated into the main stream of obstetric practice during the past four decades(12). Using sonography to estimate fetal weight has limitation including but not limited to the following: maternal obesity, oligohydramnios, anterior placentation, reduced visualization of fetal body structure and inadequate trained personnel(12, 13).
In one large cohort study in Israel, to assess and compare the accuracy of twenty-three models of sonographic fetal weight estimation, they found greater accuracy for models that used 3 or more fetal biometrics. These biometric are FL, AC, BPD, and HC(14). In contrary to this, another large cohort study, twenty-six models of sonographic fetal weight estimation were used and showed that fetal weight estimations based on AC alone were more accurate than models based on FL, AC + FL, or AC + BPD(15).
Almost all the currently used formulas for estimating fetal weight have significant degree of disparity, and various studies have been done to compare the accuracy of different methods of estimation. However, significantly reducing potential perinatal complications associated with labor of both small and excessively large fetuses requires, accurate estimation of fetal weight occurs before deliveries(12).
In Uganda, there is no formula that has been recommended for use across entire birth weight ranges due to lack of validation information. And data on the weight of Ugandan fetuses are scarce.
This study was, therefore, carried out to sonographically estimate fetal weights, in a population of Ugandan pregnant women, in a tertiary hospital in Kampala. Accuracy of fetal weight estimation using five most commonly used formulas (Hadlock 1, Hadlock 2, Hadlock 3, Hadlock 4, and SHEPARD) in the three strata of birth weights was determined and comparison of all the five formulas for weight estimation differences was done.