Final answer:
A nurse should inform a couple that the risk associated with in vitro fertilization embryo transfer (IVF-ET) includes the possibility of a tubal pregnancy, where the embryo implants outside the uterus.
Step-by-step explanation:
The nurse's response to a couple concerned about the risks associated with an in vitro fertilization embryo transfer (IVF-ET) should include the risk of B. Tubal pregnancy. Also known as an ectopic pregnancy, this occurs when the embryo implants outside the uterine cavity, often in the fallopian tubes. While other risks such as congenital anomalies and effects of substances like alcohol on embryos are valid concerns in pregnancy, the question specifically relates to risks directly following IVF-ET, with tubal pregnancy being one of the more immediate and relevant risks.