Introduction: Fetal and maternal health problems lead to increase in incidence of preterm birth that has become a major concern in obstetric practice. Perinatal survival depends crucially on a sufficiently sized and a functionally developed cardiopulmonary system. So it is extremely important to diagnose lung maturity before birth because of the increase in the indications for early induction of labour. In these conditions, assessing the lung maturity will decide timing for inducing labour. Fetal MRI is a recently developing field that provides adequate information regarding the size, structure and biochemical maturity of developing Fetal lung that overcomes the adverse effects of amniocentesis. Therefore a ratio is considered for comparing the signal intensity of the Fetal lungs with that of another structure at a comparable depth. The ideal criteria for the reference structures are sufficient size, close proximity to the lung, homogeneity and stability through the pregnancy.
Aim: Our aim was to establish a linear relationship between the estimated gestational age and the Lung- Liver Signal Intensity Ratio (LLSIR) values and to ultimately predict the lung maturity from this relationship.
Materials and Methods: The patients for this study were selected from the antenatal outpatient department of a large medical college hospital in Chennai, India. The study population consisted of a total of 50 patients who were referred from the antenatal OPD for MRI for various other indications. The liver and lung images were taken in the same imaging plane for the analysis either in the coronal or sagittal view.
Results: Magnetic resonance imaging of 50 cases were carried out during 19th and 40th week of gestationin antenatal women with age group from 23 to 31 years. LLSIR was calculated by taking the ratio of lung and liver signal intensity. The range of LLSIR is 1.54 to 4.03(2.808+0.739, mean+SD). There was no significant correlation between the liver intensity and EGA. The range of liver intensity was from 175 to 707 (425.08+115.22, mean+SD). The Pearson correlation coefficient between liver intensity and EGA was 0.232(p<0.053) that showed no correlation between liver intensity and EGA. Linear regression analysis does not show a statistically significant association between liver intensity and EGA (r2 0.034, p<0.105).
Conclusion: We conclude that the lung to liver signal intensity ratio is steadily increasing with increasing gestational age as confirmed in other studies. As fetal lung maturity increases with increase in gestational age, lung to liver signal intensity ratio can be used to assess the respiratory outcome of the neonates.