Leto (Λητώ) is from the Lycian lada (woman, wife) — the Greek Titaness daughter of Coeus and Phoebe. Mother by Zeus of the twin gods Apollo and Artemis — pursued by a jealous Hera through every country and forbidden refuge on any land; at last gave birth on the floating island of Delos, which Zeus secured with chains to the seabed for the event. Artemis was born first and immediately helped her mother deliver Apollo — for which Artemis became the goddess of childbirth. Worshipped throughout Lycia (now southern Turkey) as a primary regional goddess.
Featured in the Homeric Hymn to Apollo and Callimachus's Hymn to Delos.
Leto does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Leto reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.