Table 3.

Advantages and disadvantages of different biomarkers for the identification of Hb Bart’s hydrops fetalis.

	Advantages	Disadvantages
Sonographic markers	Non-invasive technique High predictive performance	Require specialized sonographers Require specific equipment Operator-dependent
Biochemical markers	Non-invasive technique Can perform simultaneously with second trimester Down syndrome screening	Poor predictive performance Require validation Other conditions such as infection can interfere with the result
Cell-free fetal DNA	Non-invasive technique High predictive performance Can perform simultaneously with Down syndrome screening	Relatively high costs Complex techniques and laboratory device Requires further validation. Thus, the search for other biomarkers is continuing
Extracellular vesicles	Non-invasive technique Contain molecular information of dynamic cell and tissue states of disease pathophysiological changes and complications Compatible with multiple etiologies of hydrop fetalis	Relatively high costs Complex techniques and laboratory device Predictive performance requires further studies