Continuity mistake: In the scene where Paltrow awakens the next morning after the birth you see her both her arms past her elbows and there is no sign of an injection wound on her right arm where Lange gave her the morphine shot. Yet later in the kitchen during the pivotal confrontation scene with Lange when Paltrow pulls up her sleeve to show her right arm as she explains how Lange tried to kill her the night before, there is a large large black and blue mark wound at the injection site on her right arm.
Continuity mistake: At delivery, Helen's roots are showing. The morning after, her hair is perfect, and the belly is gone. When did she had the time to dye her hair, and how did the belly disappear in only one night?
Other mistake: After Gwyneth Paltrow gives birth to her baby in Jessica Lang's room, the bottom half of her dress and part of the mattress is soaked in blood. A blanket is thrown over her to cover the sight by Lang when her husband walks in. He seems to have stayed there all night without having smelled it.