Final answer:
The couple in the question is experiencing secondary infertility, which is diagnosed when a couple is unable to conceive or carry another child to term after having had one or more children previously.
Step-by-step explanation:
The couple described in the question is exhibiting secondary infertility, which is the inability to become pregnant or to carry a baby to term after previously having one or more children.
In this case, as they already have a 3-year-old daughter and a 7-year-old son, and they have been trying to conceive for a year without success, secondary infertility is their current condition.
Infertility can be related to factors such as age, health, lifestyle, or specific issues with reproductive systems, and it can affect both men and women. Although they have conceived before, there are still many potential causes for their difficulty in achieving another pregnancy.