Butter Fly. I like it.
Actually, I would suggest that the term pregnant fly is more commonly understood to be flies where the distance between the body and the wing is more than one strike as per Cottle.
It is called a pregnant fly because it has "baby" flies embedded in the position e.g.
ATM SPX "non-pregnant" Fly is:
1275/1280/1285
An example pregnant fly would be:
1270/1280/1290 (note that it is equidistant)
This fly has 4 baby flies embedded in it. As per Cottle, the easy way to calculate that is to square the number of strikes between the wing and body. In this case it is 2 squared and hence there are 4 baby flies embeded.
In case you were wondering, the 4 baby flies are:
1270/1275/1280
1275/1280/1285
1275/1280/1285
1280/1285/1290
Why is it important to be able to dissect your position this way? Well if you know that a butterfly has maximal value when ATM then you can decide to sell some of the flies embedded in the position when it makes sense to do so etc. if you feel like taking profits or taking money off the table.
Where you have a fly where the strikes are not equidistant, it might be referred to as a skip-strike fly amongst other names.
If you want to call that a pregnant fly too then you are free to do so but some people might get confused by the differing terminology. Like any industry, half the battle is understanding the lingo.
MoMoney.
Quote from optioncoach:
A Prego FLy or commonly known as a pregnant Fly is a butterfly but the strikes are not equidistant. One wing is really far from the body so the risk graph looks "pregnant". I put a risk graph up here a few weeks ago in an EXCEL chart as an attachment which shows a sample risk graph.