Non-immune fetal hydrops: criteria (≥2 cavities) and algorithm for identifying the cause
Definition and ≥2 cavities criterion
Non-immune fetal hydrops is usually detected on ultrasound based on the presence of fluid in two or more fetal serous cavities, including skin edema, ascites, pleural and/or pericardial effusion (ISUOG, Ultrasound in Obstetrics & Gynecology, 2024). NIHF accounts for nearly 90% of all fetal hydrops cases.
Phenotypes of fluid accumulation
According to a series of 55 NIHF cases, fluid accumulation in a single cavity was noted in 25.5% (14/55), while accumulation in more than one cavity was found in 74.5% (41/55). Associated structural anomalies were identified in 16.4% (9/55).
| Prenatal phenotype | n (%) |
|---|---|
| Fluid accumulation in a single cavity | 14 (25.5) |
| — without associated structural anomaly | 12 (21.8) |
| — with associated structural anomaly | 2 (3.6) |
| Fluid accumulation in >1 cavity | 41 (74.5) |
| — without associated structural anomaly | 34 (61.8) |
| — with associated structural anomaly | 7 (12.7) |
Etiology of NIHF
According to ISUOG (2024), the etiologies of NIHF include viral infection, cardiac disease, chromosomal anomalies, and hematological and metabolic disorders. New hematological causes of fetal anemia leading to the development of hydrops have been described.
Algorithm for identifying the cause
Following diagnosis establishment, a search for the underlying cause should be undertaken. According to ISUOG principles (in the context of searching for the cause of fetal pathology), this search should include detailed anatomic scanning (anomaly scan) and screening for viral infections—cytomegalovirus, rubella, and toxoplasmosis.
The specific list of laboratory investigations and the sequence of diagnostic steps specifically for NIHF are not detailed in the fragments provided—[refer to] the complete text of the guideline for details.
Frequently asked questions
How many cavities must be involved to diagnose hydrops?
Fluid must be present in two or more fetal serous cavities, including skin edema, ascites, pleural and/or pericardial effusion (ISUOG, 2024).
What proportion of hydrops cases are non-immune?
Non-immune fetal hydrops accounts for nearly 90% of all hydrops cases (ISUOG, 2024).
What etiologies of NIHF should be considered?
Viral infection, cardiac disease, chromosomal anomalies, hematological and metabolic disorders (ISUOG, 2024).
Which infections should be screened for when searching for the cause?
According to ISUOG principles, screening includes cytomegalovirus, rubella, and toxoplasmosis as part of the etiological search and detailed anatomic scanning.
How frequently are associated structural anomalies encountered?
In a series of 55 NIHF cases, associated structural anomalies were identified in 16.4% (9/55).