You're right that Insulin does not cross the placenta in significant amounts. It the need to use insulin is Indicative of poorer glucose control in general (not your fault just what it means if that makes sense). With poorer glucose control comes more glucose to the baby meaning baby produces more insulin and stores more fat. Insulin in itself is a growth hormone and works like many other growth hormones the body produces. Also Injected Insuln is an imperfect science. Unlike the body which secretes just the right amount all the time with an injection you are having a large bolus shot maybe two to four times a day. This means your sugar will bounce a lot more, it will go down when you have the Injection and tend to swing up again when the time for the next injection draws near. These swings means the baby's pancreas has to work harder eyc etc. unlike in a perfectly working pancreas where the curve of blood sugar levels is a lot flatter.....am I making sense.

Sounds like you need more carbs, look at low GI carbs as much as possible. Basmati rice, etc. have a look at the glycemic index website for more Info on better carbs to eat. But is you need Insuln, you need Insulin, no point star ing yourself and bubba just to stay off it.