if your pearls are 1938 and Cultured and not Natural Pearls which are very valuable and very rare, then it would appear your pearls are of Japanese origin - Japan dominated pearl culturing in the 20th century.
Few of the early products however resembled the round, lustrous gems associated with Japanese cultured pearls of today. Most were quite small and irregualr in shape more like half pearls (mabe). By the 1920s, round pearls 2-3 mm in diameter were becoming more common and fueled a fashion fury for cultured pearls. Pearls were being cultured by Japanese firms operating primarily out of Indonesia and the Philipines.
In 1931, a total of 51 Japnese farms produced over one million pearls! During that decade, farmers began experimenting and collecting embryonic oysters adn raising them in tankd so they would not have to rely on oysters collected in teh wild. This caused a great leap in production. Within seven years, 289 farms cultured 11 million pearls, nearly all were for export.
(Muller, 1997, "Cultured Pearls: The First Hundred Years", Golay Buchel, KK, Tokyo, 18pp)
World War II devasted the pearling industry along with the rest of the Japanese economy, with only one-third of the farms able to remain in production, and even these were at a subsistence level. During the post-war construction, Mikimoto's internationally renowned brand helped the nation to recover. (Strack, "Pearls" 2006).