Observed to expected lung area to head circumference ratio (O/E LHR) as an indicator for pulmonary hypoplasia in fetuses with congenital anomalies of the kidney and urinary tract (CAKUT)

Introduction In fetuses with congenital anomalies of the kidney and urinary tract (CAKUT) perinatal mortality is mainly attributed to end-stage renal disease and severe pulmonary hypoplasia. In cases of congenital diaphragmatic hernia (CDH), the O/E LHR has been established as an indirect assessment of fetal lung volume and as a predictive marker for neonatal outcome. Nevertheless, no O/E LHR values have been previously reported in CAKUT cases. Aim of the study was to assess the O/E LHR and its potential use in expressing severity of pulmonary hypoplasia in such cases.

Methods A retrospective single-center study included pregnancies complicated by CAKUT between 2007 and 2018. All ultrasound examinations were performed by advanced specialists in prenatal medicine certified by the German Association for Ultrasound in Medicine (DEGUM). Prenatal diagnosis of CAKUT was divided into three categories based on mechanism and expected severity of lung hypoplasia: a) bilateral renal agenesis (lung hypoplasia due to oligohydramnios), b) CAKUT with an obvious increase of intra-abdominal pressure (lung hypoplasia due to diaphragmatic displacement) or c) CAKUT without increase of intra-abdominal pressure. The right LHR was calculated for each fetus by two independent specialists. The O/E LHR was calculated as Observed LHR / Expected LHR x100.

Results We identified 64 eligible patients. Of these, 41 women continued (group A) and 23 terminated pregnancy (group B). The LHR was impaired in both groups with median O/E LHR of 46.4% and 41.8% respectively (p=0.561). Interestingly, the mean O/E LHR did not differ significantly between the three clinical categories. However, median O/E LHR was always lower in fetuses with bilateral renal agenesis and CAKUT with increased intra-abdominal pressure than in CAKUT without increased intra-abdominal pressure, corresponding to the expected severity of lung hypoplasia. An earlier gestational age at assessment of O/E LHR (p<0.05) as well as at detection of amniotic fluid abnormality (p<0.05) in group B, indicate the severity of underlying disease in these cases ([Abb. 1]).

Abb. 1  

Conclusions The overall median O/E LHR of 43.9% underlines that in comparison to healthy fetuses, fetuses with CAKUT present with impaired lung development and pulmonary hypoplasia. Given the fact that O/E LHR is an established prognostic marker in CDH cases and can discriminate between survivors and nonsurvivors [1], further research should be done to evaluate the O/E LHR as a potential predictive marker for perinatal outcome in cases with CAKUT.

Publication History

Article published online:
15 November 2023

• References

• 1 Antenatal-CDH-Registry Group. Jani J, Nicolaides KH, Keller RL, Benachi A, Peralta CF, Favre R, Moreno O, Tibboel D, Lipitz S, Eggink A, Vaast P, Allegaert K, Harrison M, Deprest J. Observed to expected lung area to head circumference ratio in the prediction of survival in fetuses with isolated diaphragmatic hernia. Ultrasound Obstet Gynecol 2007; 30: 67-71