Vitamin K deficiency bleeding of the newborn practice

A 5-week-old girl is brought to the emergency department after two episodes of vomiting and an hour of unusual drowsiness. She was born at home at term after an uncomplicated pregnancy and has been exclusively breastfed. She is pale and irritable, the anterior fontanelle is full, and there are two bruises over the left thigh that the parents cannot account for. She is afebrile and there is no history of injury. Which one of the following items of the birth history is most important to establish?