Final answer:
The mother least likely to be at risk of puerperal infection is the one who had a typical vaginal birth of a 3200-gram infant without additional complications or risk factors.
Step-by-step explanation:
Among the four new mothers mentioned, the one least likely at risk for developing a puerperal infection would be the mother who gave birth vaginally to a 3200-gram infant (option 3). This scenario appears to be the most typical and lacks the presence of risk factors known to increase the likelihood of postpartum infections. Increased numbers of vaginal exams, as in option 1, a history of previous puerperal infections, as in option 2, and prolonged rupture of the membranes, as in option 4, are all factors that can enhance the risk of puerperal infection. As Ignaz Semmelweis discovered in the 19th century, proper hygiene and handwashing protocols are essential to prevent the spread of infections, which is particularly relevant to the context of option 1.