A congenital diaphragmatic hernia (CDH) is a hole in the diaphragm, the muscle that helps with breathing and separates the chest and abdomen. This defect can allow the liver and bowel to move to the chest cavity and interfere with lung development, affecting lung and heart function in newborn babies. At birth, respiratory insufficiency and pulmonary hypertension contribute to poor outcomes. About one in every 3000 babies may be affected and the problem can be diagnosed during a routine mid-pregnancy ultrasound at around 20 weeks. For babies born with a CDH, surgery in early life is necessary, but even with new surgical techniques there can be a poor outlook and many long-term medical problems. Treatments are now possible in pregnancy. Interventions described to date include maternal antenatal corticosteroid administration and prenatal tracheal occlusion to improve lung growth and maturity by obstruction of the fetal trachea. This increases airway pressure by preventing secreted lung fluid from leaving the lungs resulting in growth and expansion of the lungs. There are potential side effects and complications for the mother with this procedure as the uterus and amniotic sac are entered in order to gain access to the unborn baby.

This review aimed to compare the new treatments used in pregnancy with standard current care, which is surgery to reduce the herniated abdominal contents and close the diaphragmatic defect in the first few days of life following stabilisation of the newborn in a neonatal intensive care unit.

We included three randomised controlled studies (involving 97 women). The quality of the studies was variable and a number of this review's important outcomes were not reported in the trials.

Two studies compared in-utero fetal tracheal occlusion with standard postnatal repair, but differences between the two studies meant that we were unable to combine the data in our analyses. Neither study reported on perinatal deaths. In single studies, in-utero fetal occlusion was associated with a slightly lower gestational age at birth but no clear difference in the risk of preterm birth before 37 weeks; the occurrence of pulmonary hypertension was reduced. there was no difference between groups in terms of preterm rupture of membranes < 37 weeks or maternal infectious morbidity and there were no maternal blood transfusions. Long-term infant survival was improved with in-utero tracheal occlusion in one study, but not in the other.

In the third study, antenatal corticosteroids were compared with placebo and there was no difference in the number of perinatal deaths. Nor was there any difference in terms of the number of days that babies were given mechanical ventilation or the number of days babies spent in hospital.

We conclude that the current evidence is too limited by small numbers of pregnancies and the variable methodological quality of the trials to recommend intervention (treatment) in pregnancy for women and their unborn babies with CDH. Further high-quality trials are needed in this area. WIth regard to the administration of antenatal corticosteroids, there remains a gap in current research, and a large, high-quality trial should be undertaken to answer this unresolved question. More studies are needed to further examine the effect of in-utero fetal tracheal occlusion on important neonatal outcomes and long-term infant survival and health. Long-term follow-up is of particular importance, and should include morbidity and mortality measures. Further studies should examine the benefits of an in-utero intervention in relation to the severity of the congenital diaphragmatic hernia (i.e. moderate and severe). Indeed, there are three ongoing studies, being conducted by European, North and South American fetal medicine centres, which will contribute to this gap. Ongoing research and any implementation into clinical practice should include standardisation of the procedure, inclusion criteria and long-term childhood follow-up.