In her first public statement since her pregnancy was announced, Serena Williams has indicated she intends to return to tennis after the birth of her first child.

Williams posted a message to her baby on her Instagram account on Monday. “I can’t wait for you to join the players box next year. But most importantly, I am so happy to share being number one in the world with you,” wrote Williams. The baby is due later this year.

Williams also reclaimed the world No1 spot on Monday, although the woman she replaced, Angelique Kerber, can win back that ranking if she wins two matches at this week’s Porsche Grand Prix in Germany. Williams has now been No1 for a total of 317 weeks, which is third all-time behind Steffi Graf and Martina Navratilova.

Williams will be 36 if she returns at the start of next year but her trainer, Mackie Shilstone, is confident she will still be able to perform at the highest level. “Without a doubt I think she will come back and be even stronger – because she will be playing for two,” Shilstone told the Guardian last week. “If she sets foot on the court she will come to play. I hate using the word “star” but Serena is a star in the true sense. She is just unique.”

Several tennis players have won grand slams after giving birth. Belgium’s Kim Clijsters had a baby in 2008 then won the US Open in 2009 and 2011, as well as the Australian Open in 2011. Margaret Court Smith, whose grand slam record Williams is chasing, won three of her 24 championships after having a child in 1972