Scans use ultrasound not radiation, but ultrasound is not definitely 100% safe.
One study has shown increased IUGR for babies scanned 5 times or more compared to babies only scanned once or twice.
Other studies have found that ultrasound can interfere with brain development (in animal studies), others (in humans) have found they heat tissue, can cause cavitation, and that the sound is very loud (potentially harmful to the foetus's hearing).
Not saying don't have them, but definitely I think it's wise to keep it to a minimum and only have them if medically indicated, rather than 'just in case'.
Remember also that around 99% of women prior to 1980 had no scans at all, and complications were not significantly different/higher than they are now.
I've chosen to have no scans or dopplers this pregnancy.
At 28 weeks a midwife (not my usual one) felt my baby was head down. And yesterday my usual midwife felt my bump and also said baby is head down, and also heard the heart beat really clearly with the pinnard and it's 140bpm.
I'm also measuring a week 'behind' but the bump is growing at the right rate as I measured 27 at 28weeks and 30 at 31 weeks and I'm still on the 50th centile on the growth chart so not worried