Progress in intrauterine assessment of the fetal lung and prediction of neonatal function

Fetal Lung Volumes by MRI: Normal Weekly Values From 18 Through 38 Weeks' Gestation

OBJECTIVE

The purpose of this study is to establish normal total fetal lung volume reference ranges from 18 to 38 weeks' gestation at 1-week intervals.

MATERIALS AND METHODS

A retrospective analysis of 665 patients who underwent fetal MRI at two tertiary fetal centers from 2001 to 2013 was performed. Total fetal lung volume was measured in at least two planes, either manually or using a 3D workstation. The mean, median, SD, minimum, maximum, and lower and upper quartiles for total fetal lung volume were determined per gestational week. A t test was used to compare our values to previously reported values. A new formula to calculate total fetal lung volume derived from our data was created using a regression model. Comparisons between total fetal lung volume obtained by different imaging planes and manual versus semiautomatic calculation were also performed.

RESULTS

The mean normal total fetal lung volume showed a weekly increase from 18 through 35 weeks' gestation. Means were compared with the expected total fetal lung volume generated by the Rypens formula, showing statistically significant lower mean total fetal lung volume from week 19 to week 22 (p < 0.05). Comparison between our data-derived total fetal lung volume formula and the Rypens formula showed very similar values at every gestational age. No difference in total fetal lung volume was seen when comparing imaging planes or manual versus semiautomatic methods.

CONCLUSION

Measured mean total fetal lung volume values at 19-22 weeks are significantly lower than those predicted by the Rypens formula. Therefore, we propose preferential use of our values for prenatal counseling and delivery planning.

Prenatal diagnosis, prediction of outcome and in utero therapy of isolated congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) can be associated with genetic or structural anomalies with poor prognosis. In isolated cases, survival is dependent on the degree of lung hypoplasia and liver position. Cases should be referred in utero to tertiary care centers familiar with this condition both for prediction of outcome as well as timed delivery. The best validated prognostic indicator is the lung area to head circumference ratio. Ultrasound is used to measure the lung area of the index case, which is then expressed as a proportion of what is expected normally (observed/expected LHR). When O/E LHR is < 25% survival chances are < 15%. Prenatal intervention, aiming to stimulate lung growth, can be achieved by temporary fetal endoscopic tracheal occlusion (FETO). A balloon is percutaneously inserted into the trachea at 26-28 weeks, and reversal of occlusion is planned at 34 weeks. Growing experience has demonstrated the feasibility and safety of the technique with a survival rate of about 50%. The lung response to, and outcome after FETO, is dependent on pre-existing lung size as well gestational age at birth. Early data show that FETO does not increase morbidity in survivors, when compared to historical controls. Several trials are currently under design.

Timing of lung size assessment in the prediction of survival in fetuses with diaphragmatic hernia

OBJECTIVES

To investigate whether the prediction of postnatal outcome of fetuses with isolated congenital diaphragmatic hernia depends on the gestational age at assessment using the fetal observed to expected (O/E) lung area to head circumference ratio (LHR), by comparing the performance of the test at 22-23 weeks with that at 32-33 weeks of gestation.

METHODS

Following prenatal diagnosis of isolated diaphragmatic hernia before 22 weeks, we evaluated the O/E LHR at 22-32 weeks and again at 32-33 weeks of gestation. Only cases liveborn beyond 34 weeks of gestation and with postnatal follow-up available until discharge from the hospital were included. Regression analysis was used to examine the effect on postnatal survival of O/E LHR, gestational age at delivery, side of the diaphragmatic hernia and intrathoracic position of the liver. Wilcoxon rank test for paired samples was used to compare median O/E LHR at 22-23 weeks and 32-33 weeks, in babies who survived and in those who died. Receiver-operating characteristics (ROC) curves were constructed for the prediction of survival by O/E LHR at 22-23 weeks and at 32-33 weeks.

RESULTS

In total, 53 pairs of measurements could be assessed. Univariate logistic regression analysis demonstrated that significant predictors of survival were the presence or absence of intrathoracic herniation of the liver, the O/E LHR at 22-23 weeks and the O/E LHR at 32-33 weeks of gestation. Multivariate logistic regression analysis demonstrated that only O/E LHR at 22-23 weeks or 32-33 weeks provided significant independent prediction of survival. The median O/E LHR at 22-23 weeks was not significantly different from that at 32-23 weeks either in survivors or in babies that subsequently died in the neonatal period (P = 0.25 and P = 0.09, respectively). The area under the ROC curve for prediction of postnatal survival from the O/E LHR at 22-23 weeks was 0.789 (P < 0.001) and that for prediction from the O/E LHR at 32-33 weeks was 0.842 (P < 0.001).

CONCLUSIONS

In isolated diaphragmatic hernia, O/E LHR measurement at 22-23 weeks as well as at 32-33 weeks provides useful independent prediction of subsequent survival. The prediction of postnatal survival using O/E LHR is independent of the timing of assessment.

Reliability of the lung-to-head ratio as a predictor of outcome in fetuses with isolated left congenital diaphragmatic hernia at gestation outside 24-26 weeks

OBJECTIVE

The purpose of this study was to investigate the relationship between lung-to-head ratio (LHR) and gestational age (GA) in fetuses with isolated left congenital diaphragmatic hernia and to determine the applicability and reliability of LHR to predict postnatal outcome beyond 24-26 weeks of gestation.

STUDY DESIGN

The institutional review board approved this retrospective review of the University of California, San Francisco, Fetal Treatment Center database for cases with left congenital diaphragmatic hernia who were referred between March 1995 and June 2004. LHR was determined at the initial evaluation. One hundred seven live-born fetuses at 20-34 weeks of gestation (excluding cases that were lost to follow-up, with factors that potentially could influence the LHR measurement or postnatal outcome, or that were terminated electively).

RESULTS

The median GA at LHR measurement was 25.6 weeks; the median LHR was 1.01; the median GA at birth was 37.7 weeks; and the overall survival rate was 59% (64/107). The median LHR of nonsurvivors was significantly lower than that of survivors, but neither GA at LHR measurement nor at delivery was significantly different between the groups. Multiple logistic regression analysis confirmed LHR to be an independent predictor of postnatal survival, and receiver-operator characteristic curve analysis demonstrated that an LHR of > or = 0.97 has the highest performance in predicting postnatal survival. When fetuses were grouped by GA at initial LHR measurement to determine reliability of LHR, specifically with respect to GA, in the 26-34 and 24-26 weeks of gestation groups, median LHR of survivors was significantly higher than that of nonsurvivors, and receiver-operator characteristic curve analysis confirmed LHR to be a reliable predictor of postnatal survival. However, for fetuses at 20-24 weeks of gestation, there was a trend toward a higher LHR in survivors, although this did not reach statistical significance.

CONCLUSION

A significant positive linear relationship exists between LHR and GA at the time of measurement, such that LHR reliably predicts postnatal survival in fetuses with left congenital diaphragmatic hernia at 24-34 weeks of gestation and less reliable at 20-24 weeks. However, given the limitations of a retrospective, cross-sectional study, further prospective longitudinal studies that will investigate the change of LHR with GA and its association with fetal outcome are necessary.

Fetal Body Volume: Use at MR Imaging to Quantify Relative Lung Volume in Fetuses Suspected of Having Pulmonary Hypoplasia

PURPOSE

To retrospectively determine an algorithm based on fetal body volume (FBV) by using magnetic resonance (MR) imaging to calculate relative lung volume in fetuses with normally developed lungs and prospectively assess the use of this algorithm in predicting pulmonary hypoplasia in the late second and early third trimesters for fetuses at risk for pulmonary hypoplasia.

MATERIALS AND METHODS

Oral informed consent was obtained for the prospective component of this ethics committee-approved study. MR imaging lung volumetry was performed in 36 fetuses with normally developed lungs between 18 and 39 weeks gestational age by using T2-weighted single-shot fast spin-echo imaging in fetal transverse and sagittal planes. Findings were then correlated with biometric variables and gestational age. The best-performing algorithm was applied to 37 fetuses (between 18 and 29 weeks gestational age) at risk for pulmonary hypoplasia to determine observed-expected lung volume ratio. This group was stratified according to pregnancy management, and observed-expected ratios were correlated with outcome. In fetuses with isolated congenital diaphragmatic hernia (CDH) (n = 19), observed-expected ratio was correlated with lung-head ratio, neonatal survival in pregnancies managed expectantly (n = 13), and/or lung-body weight ratio at necropsy (n = 9). For that purpose, linear regression correlation was used with the Pearson correlation coefficient; P < .05 was considered to indicate a significant difference.

RESULTS

Total fetal lung volume correlated best with total FBV (r = 0.96, P < .05). Observed-expected ratio based on FBV correlated with lung-head ratio in patients with CDH (r = 0.71, P < .001) and with lung-body weight ratio at necropsy (r = 0.68, P < .05) and could be used to help predict neonatal survival.

CONCLUSION

FBV measured with MR imaging can be used as a single parameter in an algorithm and showed closest correlation with normal total fetal lung volume. In the transition from second to third trimester, this algorithm enabled calculation of the observed-expected ratio and prediction of outcome in fetuses at risk for pulmonary hypoplasia.

Prenatal intervention for isolated congenital diaphragmatic hernia

PURPOSE OF REVIEW

We aim to review the recent literature regarding early prenatal prediction of outcome in babies diagnosed with isolated congenital diaphragmatic hernia, as well as results of fetal therapy for this condition.

RECENT FINDINGS

Current survival rates in population-based studies are around 55-70%. Highly specialized centers report 80% and more, but discount the hidden mortality, mainly in the antenatal period. Fetuses presenting with liver herniation and a lung-to-head ratio of less than 1.0 measured in midgestation have a poor prognosis. Other volumetric techniques are being evaluated for use in midtrimester. Recently, a randomized trial failed to show benefit from prenatal therapy, but lacked power to document the potential advantage of prenatal therapy in severe cases. We proposed percutaneous fetal endoluminal tracheal occlusion with a balloon at 26-28 weeks through a 3.3 mm incision. In severe cases, fetal endoluminal tracheal occlusion increased lung size as well as survival, with an early (7 day) survival, late neonatal (28 day) survival and survival at discharge of 75, 58 and 50%, respectively, comparing favorably with 9% in contemporary controls. Airways can be restored prior to birth improving neonatal survival (83.3% compared with 33.3%). The procedure carries a risk for preterm prelabour rupture of the fetal membranes, although that may decrease with experience.

SUMMARY

Fetuses with severe congenital diaphragmatic hernia can be identified in the second trimester. Fetal endoluminal tracheal occlusion can be considered as a minimally invasive fetal therapy, improving outcome in such highly selected cases.

MRI of normal and pathological fetal lung development

Normal fetal lung development is a complex process influenced by mechanical and many biochemical factors. In addition to ultrasound, fetal magnetic resonance imaging (MRI) constitutes a new method to investigate this process in vivo during the second and third trimester. The techniques of MRI volumetry, assessment of signal intensities, and MRI spectroscopy of the fetal lung have been used to analyze this process and have already been applied clinically to identify abnormal fetal lung growth. Particularly in conditions such as oligohydramnios and congenital diaphragmatic hernia (CDH), pulmonary hypoplasia may be the cause of neonatal death. A precise diagnosis and quantification of compromised fetal lung development may improve post- and perinatal management. The main events in fetal lung development are reviewed and MR volumetric data from 106 normal fetuses, as well as different examples of pathological lung growth, are provided.

Current consequences of prenatal diagnosis of congenital diaphragmatic hernia

BACKGROUND

Today, the diagnosis of congenital diaphragmatic hernia (CDH) can readily be made in the prenatal period during screening ultrasound examination. Patients ought to be referred to rule out associated anomalies, and in isolated cases, prognosis is poor when the liver is intrathoracic and the lung-to-head ratio (LHR) is less than 1. In these patients, prenatal intervention aiming to reverse pulmonary hypoplasia can be considered.

METHODS

We present our current algorithm for counselling patients presenting with CDH. Patients with a poor prognosis are offered percutaneous fetal endoluminal tracheal occlusion (FETO) with a balloon, inserted at 26 to 28 weeks. We report on the evolution of technique and results in a consecutive homogeneous case series and compare outcome in cases with similar severity managed in the postnatal period.

RESULTS

Within a period of 28 months, FETO was performed between 26 and 28 weeks in 24 fetuses with severe left-sided CDH. Under general (n = 5), epidural (n = 17) or local (n = 2) anesthesia, the balloon was successfully positioned at first surgery (23/24) with a mean operation time of 20 minutes (range, 3-60 minutes). There were no serious maternal complications or direct fetal adverse effects. In the first 2 weeks after FETO, LHR increased from 0.7 to 1.7. Premature prelabour rupture of the membrane (PPROM) occurred in 16.7% and 33.3% at 28 and 32 weeks or earlier, respectively. Gestational age at delivery was 33.5 weeks. Patency of airways was restored either in the prenatal (n = 12) or perinatal period (n = 12). Early (7 days) and late (28 days) survival, and survival at discharge were 75% (18/24), 58.3% (14/24) and 50% (12/24), respectively. Half of nonsurvivors (n = 6) died of pulmonary hypoplasia and hypertension, in combination with PPROM and preterm delivery (n = 4) and balloon dislodgement (n = 2), which coincided with a short tracheal occlusion (TO) period (12 days). In the other 6, TO period was comparable to that in the 12 survivors (47 vs 42 days, respectively). In that group of 6 babies, only 2 died of pulmonary problems. Late neonatal survival (28 days) was higher with prenatal vs perinatal balloon retrieval 83.3% vs 33.3% (P = .013). In a multicentre study validating the criteria, survival till discharge in 37 comparable cases was 9% (3/32) and 13% (5/37) of parents opted for termination.

CONCLUSION

Fetuses with isolated left-sided CDH, liver herniation, and LHR of less than 1 have a poor prognosis. Percutaneous FETO is minimally invasive and may improve the outcome in these highly selected cases. Airways can be restored before birth, allowing vaginal delivery and return to the referring tertiary unit and may improve survival rate. The procedure carries a risk for PPROM, although that may decrease with experience.

Fetal intervention for congenital diaphragmatic hernia: the European experience

Fetuses with CDH presenting with liver herniation and a lung area-to-head circumference ratio of less than 1.0 have a high chance for neonatal death due to pulmonary hypoplasia. Fetal tracheal occlusion (TO) prevents egress of lung liquid, which triggers lung growth. In animal experiments, we were able to develop a minimally invasive technique for Fetoscopic Endoluminal Tracheal Occlusion (FETO) with a detachable balloon. In 2001, we demonstrated feasibility of FETO by percutaneous access in fetuses with severe CDH. In a retrospective multicenter review, we obtained LHR measurements and position of the liver in 134 cases of isolated left-sided CDH between 24 and 28 weeks. Eleven patients (8%) with LHR < 1.4 opted for termination. Overall survival of liveborn babies was 47% (58/123). LHR and position of the liver correlated both to survival. Combination of both variables predicted neonatal outcome better: liver up and LHR < 1.0 predicted a survival of 9%. When LHR < 0.6, there were no survivors irrespective of liver position. We could successfully perform endotracheal placement of the balloon in 20 cases at a median gestational age of 26 weeks. The mean duration of the operation was 22 (range 5-54) minutes. In 11 (55%) of these patients, there was postoperative prelabor (ie, <37 weeks) amniorrhexis. Membranes ruptured before 32 weeks in 35%, with a decreasing trend as experience increased. Ultrasound scans after FETO demonstrated an increase in the echogenicity of the lungs within 48 hours and improvement in the LHR from a median 0.7 (range 0.4-0.9) before FETO to 1.8 (range 1.1-2.9) within 2 weeks after surgery. The median gestation at delivery was 33.2 (range 27-38) weeks, and in 14 (70%) this occurred after 32 weeks. Surgical repair of the diaphragmatic hernia could be done in 13 babies, and in all but 1 the defect was extensive and required the insertion of a patch. Survival to discharge was 50%. These 10 long-term surviving babies are now aged 7 to 26 (median 19) months without known neurologic morbidity. Eight babies died in the neonatal period due to complications of the underlying disease. Two nonsurvivors died from other causes but with appropriately developed lungs. Improved survival coincided with increasing experience, in turn related to reduced incidence of postoperative amniorrhexis, later delivery, and a change in the policy on the timing of removal of the balloon from intrapartum to the prenatal period. Survival in eligible contemporary controls was 1/12 (8%). The presence of liver herniation and a low lung-to-head ratio (LHR <1.0) is a good predictor of poor prognosis at different tertiary centers around the world. Severe CDH may be successfully treated with FETO, which is minimally invasive and may improve postnatal survival.