Julia Grovenburg is due to give birth at the end of December 2009 -- and again in January 2010. The Arkansas resident says she is carrying two fetuses conceived 2.5 weeks apart. She's not the first woman to say she has conceived though already pregnant -- a phenomenon called superfetation.

Getting pregnant while pregnant: Superfetation occurs when a pregnant woman ovulates (rare), the ovum gets fertilized (rarer) and the fetus finds room in the womb (alert the media).

Doubters: Some medical experts say superfetation in this case is unlikely. Here's why. Her obstetrician disagrees. What he says.

Amazing multiples:Ame and Lia Herrity were conceived three weeks apart and born together in 2007 (by cesarean section). Thomas and Harriet Mullineux share a similar story.

Room for doubt: In 2002, Italy's Flavia D'Angelo announced that she was carrying triplets she conceived while she was six months pregnant. Or so she said.

Major misconceptions: Pregnancy stops ovulation -- usually. But breast-feeding and ''it's my first time'' are among birth control myths.

Other multiples: If a woman is carrying two fetuses fathered by two different men, the medical term is this.

Are they twins? Here's a refresher on twins. Now you can join the debate on how to categorize the in utero Grovenburgs.