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
Condition: Preterm Birth; Low Birth Weight
MeSH terms: Premature Birth; Body Weight; Birth Weight
Study type: Observational

Summary: 
      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 low birth weight using ultrasound conducted
      between 6-20 weeks for the predicted estimated date of delivery (EDD) as the gold standard.

      Secondary objectives of the study are, 1) to develop the regression equations that predict
      gestational age and low birth weight using foot length, 2) to assess the use of foot length
      measurement as a screening tool to identify LBW or preterm infants in a community-based
      setting, and 3) to develop percentile charts of foot length for gestational age and low birth
      weight

      Methods:

      This test validation study will be conducted in Global Network's Maternal and Newborn Health
      Registry catchment area. All live birth singleton babies who have a first-trimester
      ultrasound for gestational age and birth weight within 48 hours of birth will be included in
      this study. Stillbirths, multiple pregnancies, gross congenital malformations such as neural
      tube defects, omphalocele, etc., club foot, and babies with chromosomal abnormalities such as
      Down syndrome that make measuring foot length difficult, will be excluded from the study.
      Gestational age will be assessed using ultrasound between 6-20 weeks of gestation by a
      trained sonographer working in the registry. Neonatal assessment having neuromuscular, and
      physical signs will be conducted by the research assistants (RA). RA will be taking
      anthropometric measurements such as birth weight using calibrated weighing scales, foot
      length, mid-upper arm circumference, and fronto-occipital circumference.

      The data will be entered in Epicollect data five. Sensitivity, specificity, positive &
      negative predictive value, likelihood ratios, and diagnostic accuracy will be done using
      different cut-offs of foot length against ultrasound estimated gestational age and birth
      weight. Receivers operating characteristics (ROC) curves will be generated to identify the
      optimal cut-off point for foot length taken within 24 hours of birth for identification of
      prematurity and LBW (based on first-trimester ultrasound) with ≥80% sensitivity. Linear
      regression will be done for estimating predictive values of foot length by GA. Pentile charts
      for foot length (FL) against GA will be derived. Bland Altman's analyses will identify and
      quantify any biases inherent to the tool.

      Public health implications:

      If these equations predict gestational age and birth weight with accuracy, an android-based
      application can be developed for health care providers (HCP) who simply measure foot length
      and enter it into the application to identify preterm &/or low birth weight along with
      referred guidelines for early treatment. This is one step closer to Every Newborn Action
      Plan's goal of lowering neonatal mortality to 12/1000 LB by 2030.
    


Intervention name(s): Foot length
Intervention type(s): Diagnostic Test
Intervention description(s): Foot length will be measured from the midpoint of the heel to the longest toe.
Observational model: Other
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Singleton alive newborns
      
Keywords: Gestational age; birth weight; Diagnostic accuracy; Regression equation; Correlation