As said above, 37 weeks is full term. Baby's lungs should be fully developed by then. If there's concerns that maybe baby's growth restricted or something, I wonder if just giving you steroids to mature the baby's lungs just in case would be less of a worry than an amnio?
And, DaisyBee, 4.5-5lb isn't really tiny to us NICU nurses, so it's good to know your little one might still not have ended up in NICU even if she'd been that small. But now I'm all scared of delivering a baby >7lb, as that looks huge to me!