Like HM,we up the feed during the last 2-3 weeks, and double for the last ten days (more if she clears it quickly). The last ten days is when the piglets put on much of their growth,until then they are really tiny.
After birth, there are a number of rules of thumb. One is to feed an extra pound per piglet each day until you reach the number of piglets eg with 12 piglets you would feed 6lbs (mums normal feed) on day 1, 7lbs day 2, 8lbs day 3 until you get to 18lbs on day 12 (mums normal 6lbs plus 12 pounds - 1 per piglet). Since all sows are different, we tend to feed to appettite and condition- feed more to a sow who is losing condition, less to one that is able to maintain. Normally they go off food for a couple of days, but then we feed double in the first week,and then watch condition and add/subtract.
It would be highly unlikely that lack of feed in the last few weeks would cause two healty but no more, more likely you wouldhave several small, or somemumified or stillborn in addition to the two.