Final answer:
The best response to the mother's concern about her baby's size is to inform her that large babies are common with gestational diabetes.
Step-by-step explanation:
The best response from the nurse to a client who has given birth to a large infant and has a history of gestational diabetes would be: b) Large babies are common with gestational diabetes. This statement addresses the mother's concern directly and provides an explanation related to her medical condition. It is well-established that gestational diabetes can lead to macrosomia, which is the medical term for a baby that is significantly larger than average at birth. It is essential for both the mother and baby to monitor their blood sugar levels after delivery, as gestational diabetes can influence the baby's health.