America's Serena Williams (left) greets France's Marion Bartoli during a tournament in New York on Monday. Pic/AFP

Serena Williams has revealed preparing for her return to tennis following the birth of her first child has been difficult and that she still has doubts about how she can keep going. Williams makes her comeback to the WTA Tour this week when she takes on Kazakhstan's Zarina Diyas in the opening round of the BNP Paribas Open in Indian Wells.