The '-sha' suffix is often used in short/informal versions of Russian names which might contribute to a lot of confusion since many people use the informal version of their name as formal overseas.

With the formal versions, the vowel rule is a good bet, but a lot of the informal versions for both male and female names end in 'sha' (and thus 'a').

Here's a few examples:

- Natalia: Natasha (Female)

- Aleksandr, Aleksandra: Sasha (Male/Female)

- Aleksei: Lyosha (Male)

- Daria: Dasha (Female)

- Oksana (Female)

- Nikita (Male)

- Yurii: Yura (Male)

- Pavel: Pasha (Male)

Keeping it terse here, the list goes on and on, you can come up with an 'a'-endng informal version of almost every male name.