On the same principle that it is tempting fate to count things too closely, there was previously a prejudice in many people's minds about weighing newborn babies. First noticed by Chambers (1878: ii. 39), from Suffolk, although it was clearly well entrenched already, the belief is reported a number of times into the 20th century, and was not even extinct in the 1950s (Folk-Lore 68 (1957), 414). Opie and Tatem also record an earlier reference to the weighing of adults being considered unlucky, published in the British Apollo (7 Sept. 1709).
Opie and Tatem, 1989: 437.