Diagnostic Accuracy of Foot Length in Predicting Preterm and Low Birth Weight Using Ultrasound Dating as The Gold Standard in a Rural District of Pakistan

Background: The burden of preterm and low birth weight babies (LBW) is high in low- and middle-income countries (LMICs). Therefore, assessment of gestational age (GA) and birth weight is important. The GA is assessed using a reliable last menstrual period (LMP), measuring fundal height, using ultrasound for dating, or postnatally using Ballard, Dubowitz, or Eregie scores. However, each method has some limitations. Pregnant women in LMIC are not able to recall LMP and are also unreliable when menstrual cycles are irregular, fundal height is often imprecise and subject to variation due to observer bias, uterine pathologies, abdominal obesity, amniotic fluid volume, fetal position, and ultrasound in a rural setting is often unreliable because lack of trained sonologist, power failures, and maintenance of ultrasound machine. Post-natal GA scoring is also lengthy, subjective, and time-consuming. Similarly, determining birth weight has many challenges. In Thatta, weighing scales are only available in health facilities, therefore, birth weight is available for babies born in the health facilities. Furthermore, even where weighing scales are available, the calibration and maintenance are not without challenges, especially in the extremely hot climate. In the majority of studies, foot length has been validated for determining GA and birth weight, with LMP serving as the gold standard, which has limitations in our population. In a meta-analysis on the diagnostic accuracy of foot length to identify preterm and LBW, researchers emphasized the need for studies using high-quality ultrasound as a reference standard for early dating. Hence, there is a need to develop a simple and effective method of GA and birth weight that healthcare providers of all levels including mid-level healthcare workers in remote areas can use with reasonable accuracy. Objectives of the study The primary objectives of the study are to determine the diagnostic accuracy of foot length in predicting GA and