Final answer:
Option A) 'is less costly' is the correct answer, as it is not a biological or health benefit, unlike the other options which correctly refer to benefits such as the amenorrhaeic effect, uterine contraction facilitation, and a potential decreased risk of breast cancer.
Step-by-step explanation:
The question "Which of the following is NOT a maternal benefit of breastfeeding?" is referring to commonly known advantages that mothers may experience from breastfeeding.
Among the options provided, B) shortens the intervals between pregnancies is a known benefit due to the amenorrhaeic effect of breastfeeding, which can act as a natural form of contraception by delaying the return of menstrual cycles. C) assists the uterus in returning to prepregnancy size is also a benefit, as the release of oxytocin during breastfeeding promotes uterine contractions to help the uterus shrink back to its original size. D) potential decreased risk of breast cancer is recognized as a benefit with some studies suggesting that prolonged breastfeeding can lower the risk of breast cancer.
Therefore, A) is less costly is the correct answer, as it is not related to biological or health benefits but rather to the financial aspect of feeding a newborn.