There's no evidence that ichthyosis leads to premature births. However, you have a 11% chance of having a preemie for your first child. Once you've had one preemie, your risk goes to 20%. Once you've had 2 preemies, your chances of another are about 45%. Speaking from experience - I have 3 preemies, so I did the research.
That said, what shot do they want to give you? Progesterone has been shown to help prevent the cervix from thinning and prevent premature contractions. It only helps, though, if the prematurity was caused by a progesterone problem. This is fairly new research, so it likely hasn't been approved yet.
In my case, I tested positive for having 2 mutated copies of a gene called MTFHR, which can cause clots, placental insufficiency, IUGR and premature birth. Ask your doctor about that - it's just a blood test. Another thing you might want to ask about is seeing an MFM in addition to the OB.
Ichthyosis-en-Confetti Type 2
Husband, Nathan - 10, Elliot - 7, Oliver - 4, all affected.
I also have an unaffected daughter, age 8.
email: jennifer at confettiskin dot com
facebook - find me on "ichthyosis mommy spot" or "friends of ichthyosis"