Continuity mistake: Alan and Marie are chatting with the doctor after the initial sonogram. Marie's hands change position few times between shots - for instance right after the "crack" joke, she lowers her hand but it's on top of her pregnant belly at the cut. (00:03:30)
Other mistake: At the first appointment in the movie, the sonogram screen says 15 weeks 1 day in the top left corner. Then the doctor goes on to say "Everything looks great for 35 weeks." (00:03:05)