You shouldn’t eat it.
The problem is not arbutin but hydroquinone, its hydrolysis product and this one is not recommended as topical treatment during pregnancy (FDA lists it as possibly embryotoxic based on animal studies though human data are lacking). Example publication
HERE.
Now, we don’t know how much arbutin turns into hydroquinone but the part that does, is systemically available and potentially harmful. If you balance the benefits of arbutin (or rather lack thereof), probably a transient/reversible increase in skin pigmentation, and the fact that you’d better be use something against stretch marks than pigment issues against a possible, irreversible damage to the unborn child and as a consequence probably to its mother too… Sure, some people put beauty first but honestly, one would wonder why someone with that attitude decided that getting pregnant were a smart idea.