DISCUSSION
In this present study, significantly higher values of the pulmonary artery acceleration to ejection time (PATET) were found in the fetuses whose mothers were complicated by IHCP. Notwithstanding detection of frequent NICU admission and respiratory distress in the IHCP group, these were not correlated with PATET. Gestational age at birth and APGAR score at fifth minutes were the most important determinants of the NICU admission and respiratory complications.
In literature, although many studies that were focused on the relationship between PATET and respiratory complications, conflicting results have been reported. Pulmonary artery acceleration time and right ventricle ejection time were first assessed by Kitabatake et al, and they reported that decreased values of both measurements have been found in pulmonary arterial hypertension 12. Fuke et al, showed that AT/ET ratio of the branches of pulmonary artery appeared to be an accurate parameter with which to predict pulmonary hypoplasia13. To date, the PATET has been investigated to predict RDS especially premature fetuses 10-14. Few studies that were focused on PATET values of late term and term fetuses showed that inverse correlation between fetal PATET value and transient tachypnea of newborns 8,15.
However, in 2010, Azpurua et al, reported that the At/Et in the main pulmonary artery waveform correlated inversely with the lecithin/sphingomyeline ratio 11. In 2013, Kim et al, demonstrated that an elevated At/Et ratio in the fetal pulmonary artery was associated with RDS as supporting Azpurua 10. The other studies that were referred above, showed contrast findings from Azpurua’s study and this study. The findings of both studies observations are similar to our study results in terms of the relationship between elevated PATET and lung immaturity. Possible explanation of it, fetal lung surfactant production is lower in IHCP than healthy fetuses and possible lung damage has been with elevated PATET.
The immunological response to tissue injury or microbial invasion involves pro inflammatory and anti-inflammatory responses in human fetuses. It has been showed that the newborns exposed to systemic inflammation in utero were with higher frequency of neonatal morbidity as a result of fetal inflammatory response syndrome that is associated with multi systemic involvement 16. Fetal lung inflammation is characterized by expression of many different cytokines and the effect of inflammation results as stimulated surfactant production. In literature, there are studies investigating inflammatory process intended for clarifying the etiology of IHCP and the pathophysiological pathways of bile acid induced inflammation affecting fetal and neonatal outcomes 17-19. Herraez et al, reported that accumulation of maternal bile-acids triggered an inflammatory response in maternal and fetal lungs and the importance of released macrophage associated phospholipase A2 in RDS development5.
Previous studies demonstrated that the RDS rate was approximately three times higher among the newborns whose mothers were complicated by IHCP20,21. Arthuis et al, also found significant difference for intensive care unit admission rates and they reported that higher biliary acid levels were in this group 20. NICU admission rate was found higher in our study group which is consistent with the previous studies. Although, respiratory distress rate (5/18) was higher in our study group, it couldn’t be found statistically significant when compare to the control group (3/37). That may be explained as all NICU admissions in the control group due to respiratory distress and lower ratio of respiratory distress in all NICU admission for the study group.
To the best of our knowledge, this is the first study that evaluates PATET in fetuses whose mothers were complicated by IHCP. The strength of this study was its prospective and well-designed and being the first study in IHCP as mentioned above. On the contrary, the main limitation was the small sample size depending on the lower incidence of IHCP and couldn’t have been categorized based on severity of the disease. Additionally, the secondary hypothesis of this study couldn’t be documented with these results.
In conclusion, higher values of the main pulmonary artery acceleration to ejection time that were detected in fetuses whose mothers were complicated by IHCP may be helpful to understand fetal lung damage secondary to IHCP. Larger prospective studies or evaluation of branches PATET values may be enlighten the prediction of respiratory complications of these newborns.