Speaking to The Times in a new interview ahead of her West End return in The King and I, the 39-year-old said: "I don't know what the plan is," adding: "Like in life, you just never know what's going to happen."
She went on to say that nevertheless, she will stay busy: "I get a bit restless when I have too much time. I don't like to ponder my own thoughts."
Earlier this month, The Sun reported that Helen's character decides to leave at the end of series 13, while Olly had been written out of scripts.
HELLO! understands that this is not the case, and that Trixie is not leaving Poplar at the end of the new series, while Olly will appear in all of the new episodes. His departure has not been confirmed.
Trixie isn't the only character whose future has been uncertain recently. At the end of series 12, fans were left concerned that Nancy (Megan Cusack) might be departing Nonnatus House after being offered a new nursing job in the countryside.
In the series finale, Nancy decided that she would make her decision after Trixie and Matthew's wedding, leaving her future up in the air.
However, during a recent roundtable discussion, actress Megan revealed that Nancy is still in Poplar in the Christmas special, which sees the nurse move into Nonnatus House with her daughter, Colette.
"Me and my daughter move into Nonnatus House," she said. "We have our own little bedsit, which is very sweet."
Detailing the new set, Megan added: "It was cute as well because we weren't allowed to see it, especially little Francesca [Fullilove], who plays Colette. She wasn't allowed to see the set until we actually went to film us going in for the first time. So it was a nice little surprise."
It's not long now until Call the Midwife returns to our screens with its annual festive episode, which begins two weeks before Christmas in 1968 with "Apollo 8 poised to circle the moon".
The Nonnatus House family set out to cheer up Sister Monica Joan, who becomes convinced that she might not see another Christmas.
Elsewhere, newlyweds Trixie and Matthew prepare for their first Yuletide as husband and wife when Trixie's brother Geoffrey pays them an unexpected visit just days before Christmas day.
Meanwhile, Cyril (Zephryn Taitte) gently intervenes when he "discovers a lost soul living alone in a dilapidated basement flat", and Nurse Crane (Linda Bassett), who is away on her refresher course, attempts to make it home in time for Christmas and is faced with "treacherously heavy snowfall."