In this prospective multicenter study, we conclude that hydropic CDH is rare, only 2.8% of all prenatally diagnosed cases, and more commonly occurring in right-sided CDH. Survival rates are low, with higher rates of non-repair. Hydrops is a clinical entity characterized by the presence of skin and scalp edema or fluid in two or more body compartments. In cases of fetal thoracic anomalies, such as CDH, it is thought to be caused by obstruction of venous return to the heart leading to elevated systemic venous pressures [23].

When using the term ‘hydrops’ in CDH, effusions in the thoracic cavity and abdominal cavity concomitant to the side of the defect, should be considered as one compartment for obvious reasons, avoiding confusion. Thus, true hydrops in CDH should refer to patients with excess fluid in at least two non-communicating compartments.

However, the presence of excess fluid in only one compartment is associated with worse outcome. Even if the association is rare, nearly 3% of all prenatally diagnosed CDH will present with fluid in one compartment, the survival rates are low (47.3%, Table 3). True hydropic CDH is even rarer, only identified in 0.35% of the prenatally diagnosed CDH cases, and more commonly occurring in right-sided CDH. Survival rates for true hydropic CDH are very low: 78% of patients with true hydrops did not survive to discharge.

Earlier studies have reported a 46% survival rate for hydropic fetuses and as high as 90% mortality rate for hydrops associated with CDH [24].

Malformations are present in half of the CDH with fluid/edema, true hydrops (fluid in at least two compartments), or non-true hydrops (fluid in 1 compartment), and more common among those who died before discharge (56% vs 42%, Table 2).

Skin edema seems to be an independent risk factor for worse outcome, with higher mortality. However, even though the pathophysiological mechanisms underlying this event remain unknown, an increased central venous pressure and/or obstructed lymphatic drainage may be the most plausible explanation [25].

Although the pathogenesis of hydrops in fetuses with CDH is poorly understood, right-sided lesions seem to be more likely to cause hydrops in CDH. Most of the cases presented here were right sided and/or had a major portion of the liver in the chest, thus the pathophysiology may be similar to other intrathoracic lesions, with mediastinal obstruction from solid organ herniation obstructing blood return to the heart. Since there is a confined space within the thorax, the herniation of a solid organ such as the liver, leaving a smaller portion intraabdominally, may lead to kinking and obstruction of the inferior vena cava, portal, or hepatic vein [26]. There are a few cases reports in the literature with the successful placement of thoraco-amniotic shunt prenatally [27].

Hydrops is more commonly associated with right-sided CDH, as many as half of the patients with hydrops have a right-sided defect, but left-sided CDH with associated hydrops has a poorer outcome, with higher rates of associated anomalies, high rates of non-repairs, and is overrepresented among children who died before discharge (75% of the left-sided CDH with hydrops will demise, probably due to the complexity of the CDH). In the absence of fetal hydrops, left-sided CDH has usually been reported to have better survival rates [28, 29].

Reasons for non-repair are the critical condition of the newborn, due to the severity of the hernia and impossibility to stabilized, the co-occurrence of other major associated anomalies or clinical deterioration non-reversible, upon parental request or the multidisciplinary teams best judgment. Despite high rates of non-repairs, good patient selection and a more aggressive surgical approach can lead to acceptable survival rates: 80% of the patients repaired survive to discharge. ECLS support was offered to the same extent to patients who survived and those hydrops patients who died before discharge.

Some of the limitations of this study is that the variable reported to the registry is limited and varying over time. Some of the parameters, e.g., hernia size and O/E LHR, were introduced in recent most versions of the CDHSG reporting form. The rate of prenatal diagnosis has increased over time and the availability for genetic testing has also changed substantially during the period the data were collected. Management protocols have evolved [30, 31] and decision-making by multidisciplinary team approach has become more standard of care in recent years. Also, the interpretation of the results cannot be universally generalized to the entire CDH population, since the data only includes patients born at or transferred to the participating centers. Another limitation if the lack of long-term follow-up data, since the data collection only comprises the time of in-hospital stay, and therefore does not consider any events occurring after the patient is discharged from the center.

In conclusion, the association of CDH and hydrops in the fetus is rare and the sole presence of excess fluid or edema in 1 compartment is associated with poorer outcome. The combination is associated with the presence of other associated anomalies and right-sided defects with liver involvement. Special attention should be given to the presence of skin edema resulting in higher mortality rates. An initially aggressive surgical approach may result in acceptable survival rates comparable to non-hydropic cases. Early decision-making regarding the aims of care clearly influence outcome, since survival varies depending on the severity of the CDH and the presence of other associated anomalies.