How many cubes are there?

Brenda, pregnant with her first child, was paying a visit to her obstetrician's office. When the exam was over, she shyly began, "My husband wants me to ask you..."
"I know, I know," the doctor said, placing a reassuring hand on her shoulder, "I get asked this all the time. Sex is fine until late in the pregnancy."
"No, that's not it at all," Brenda confessed. "He wants to know if I can still mow the lawn."