Evaluation of the Relationship Between Fetal Lung to Head Ratio and Amniotic Fluid Index in the Third Trimester of Pregnancy

Background & Objective: This study assessed the relationship between the ratio of fetal lung volume to head circumference and amniotic fluid index (AFI) in the third trimester of pregnancy. Materials & Methods: This prospective study was performed on low-risk pregnant women in their third trimester of pregnancy. Fetal lung volume was determined separately using the lung-to-head ratio (LHR) for the right and left lungs. Moreover, the AFI was evaluated, and the Pearson correlation coefficient between LHR for both lungs and AFI was investigated. Results: Overall, 112 pregnant women were included in the study. The mean ± standard deviation (SD) of fetal Observed/Expected Right LHR (O/E RLHR) and O/E Left LHR (O/E LLHR) were 113.9±0.36 and 97.13±27.87, respectively. The mean ± SD of AFI was 12.5±4.96 cm. Pearson correlation coefficient did not show a significant relationship between AFI and the left and right LHR (P>0.05). However, O/E RLHR was significantly correlated with abdominal circumference (P=0.02, r=0.2), gestational age (P=0.21, r=0.27), and fetal weight (P<0.001, r=0.27). There was a positive correlation between the number of days the infant was admitted to the neonatal intensive care unit and the volume of the right lung of the fetus (P=0.03, r=-0.2). No correlation was observed between fetal parameters and the volume of the left lung of the fetus. Conclusion: The results of this study showed that AFI in the third trimester of pregnancy was not significantly correlated with LHR.