Prevalence of Small for Gestational Age Foetuses Using Hadlock Method: An Exploration of Associated Risk Factors

Background: Small for gestational age (SGA) foetuses are associated with increased perinatal morbidity and long-term developmental challenges. In low-resource settings, limited data exists on region-specific prevalence and maternal risk factors contributing to SGA, particularly using validated biometric estimation methods like the Hadlock formula. Objective: This study aimed to determine the prevalence of SGA foetuses using the Hadlock method and explore its association with maternal risk factors, specifically passive tobacco exposure, haemoglobin levels, and systolic blood pressure. Methods: A prospective cross-sectional study was conducted at the Radiology Department of Mardan Medical Complex, Khyber Pakhtunkhwa, Pakistan, between July 1, 2022, and February 8, 2023. A total of 251 third-trimester pregnant women aged 18–45 years with singleton pregnancies were enrolled. Participants with multiple gestations, cardiac or neurological conditions, ruptured membranes, or TORCH positivity were excluded. Foetal biometric measurements (BPD, HC, AC, FL) were obtained using ultrasound to estimate foetal weight via the Hadlock method. Data were analyzed using SPSS version 27, with chi-square and binary logistic regression applied to evaluate associations. Ethical approval was obtained from the Khyber Medical University Ethics Board (DIR/ORIC/Ref/23/00013), in compliance with the Declaration of Helsinki. Results: The prevalence of SGA foetuses was 10.4% (n=26), while 89.6% (n=224) had normal estimated foetal weight. Passive smoking was reported in 19.6% (n=49) and showed a strong association with SGA (p = 0.000). Low maternal haemoglobin levels were also significantly associated with SGA (p = 0.005), with an odds ratio of 0.63 indicating increased risk. No significant association was found between maternal systolic blood pressure and SGA (p = 0.205). Conclusion: The study identified a notable prevalence of SGA foetuses using the Hadlock method and highlighted maternal tobacco exposure and low haemoglobin levels as significant modifiable risk factors. These findings underscore the importance of integrating routine ultrasound and maternal health assessments into antenatal care to reduce the burden of SGA and improve neonatal outcomes in resource-limited settings.