Actress Melissa Joan Hart is determined not to know the sex of her third child until he or she is born.

The heavily-pregnant star admits curiosity got the better of her when she first fell pregnant and a doctor let slip the sex the second time around - but this time she's determined to keep the big news a surprise until delivery day.

She says, "This time I was like, 'I am not finding out'. I told everyone."

Hart reveals she's not set on a name either - because she wants to see her child first.

She tells news show Access Hollywood Live, "We don't like to name the baby until we see it. It's kind of a superstition thing... I feel like we go to the hospital with, like, three names of each sex and the baby comes out (and) we see it and we name it."

But the actress admits her two young sons have already started coming up with names for their brother or sister: "They wanna call it Whatchamacallit Wilkerson."

The expectant father is Hart's rocker husband Mark Wilkerson.