De or het vetzwelling?

The correct Dutch article is:

de vetzwelling

Rule Words ending in -ing: almost always de. See the rule
Meaning (Dutch) (medisch) chronische, erfelijke vetverdelingsstoornis waarbij vet zich onevenredig ophopt in de benen, billen en soms armen, terwijl de rest van het lichaam slanker blijft

How to use vetzwelling

the vetzwellingde vetzwelling
this vetzwellingdeze vetzwelling
that vetzwellingdie vetzwelling
our vetzwellingonze vetzwelling
your vetzwellingjouw vetzwelling
every vetzwellingelke vetzwelling
which vetzwelling?welke vetzwelling?
a big vetzwelling / the big vetzwellingeen grote vetzwelling, de grote vetzwelling

Meaning, plural, diminutive, pronunciation and translations: WikiWoordenboek (Dutch Wiktionary) (CC BY-SA 4.0). Example sentences: Tatoeba (CC BY 2.0 FR).