Petrova is a popular Russian (feminine) surname - like Ivanova, Pavlova, or Feodorovna. They're all based on common first names, like
Ivan,
Vasily,
Fedor,
Petr,
Pavel...
Masculine forms: Petrov
Ivanov
Pavlov
Feodorov
But I don't live in Russia, so I could be wrong. (But my native language is actually Russian)