taken from the newsgroup/usenet rec.arts.bodyart: Tattoo FAQ
HOW DOES WEIGHT GAIN/LOSS AFFECT A TATTOO?
Tattoos can definitely be affected by stretch marks. Whether you will or
won't get stretch marks is apparently determined genetically, so
placement is a consideration if you are planning on getting pregnant. I
know for a fact that stretch marks can ruin a tattoo, because I have a
very small tattoo that now looks more like a blob because of a large
stretch mark running through the middle of it. Luckily, this was a
home-brewed job (the kind done with India ink and a pin wrapped in
thread) so I was never particularly attached to the artwork. :-}
If your skin stretches from weight gain and then shrinks back up without
losing its elasticity (the loss of elasticity is what results in stretch
marks), then I would expect that there wouldn't be much distortion of
the tattoo, maybe none at all.
Or, put the tattoo someplace that won't get stretched so much, like the
chest area above the breasts. My upper stomach didn't stretch much,
either, but the lower abdominal skin did stretch quite a lot. (I've seen
stretch marks on hips, thighs and arms as well--probably related to
muscle gain from weight lifting as well as general fattening/thinning.)
HOW DOES LIFTING WEIGHTS AFFECT A TATTOO?
For most people, the amount of muscle gain is nowhere near as quick or
as dramatic as what you would see with the stretching of skin on a
pregnant person. For this reason, you don't really have to worry about
your tattoo changing shape when you start lifting weights. I don't know
what would happen though, if you decide you want to be the next Mr.
Universe and you currently weigh 90 pounds.
HOW DOES PREGNANCY AFFECT A TATTOO NEAR THE ABDOMEN?
If you are planning on getting pregnant, you should be very cautious
about the placement of any tattoo near the abdominal area. Not only will
the tattoo stretch during pregnancy--there is no guarantee that the
tattoo will go back to its original shape after the birth of your baby.
Be particularly wary of getting any tattoo where the shape is important,
such as with symmetrical tribal pieces, or Celtic knots. Even geometric
patterns such as a circle could end up looking like an oval (or worse,
an irregular blob). A more "giving" image, such as that of clouds, might
suit you better.
There are two options you might want to consider: a) Do not get any
tattoos around the abdominal area at all, but limit your ink to other
parts of your torso; b) Put off getting your abdominal tattoos until
after you have had your children.
Obviously, this involves some level of family planning.