Size Newborn, but these did fit my son when he was under 5 lbs. (the boy version).
12 Pairs Preemie Socks Baby Girls Boys Premature Ruffle Socks Preemie Turn Cuff Cotton Socks Hospital NICU for Newborn (Ballet Style)
Twistover - 10 Pairs of Preemie Cotton Terry Socks for Newborn, Light Purple, Light Taro, Pink, Light Khaki, Beige, Preemie
10 Pairs Preemie Socks Ruffle Lace Ruffle Cotton Socks for Preemie Girls Boys