The Iowa Code Section 709.4 would seem to apply
709.4 Sexual abuse in the third degree.
A person commits sexual abuse in the third degree when the person performs a sex act under any of the following circumstances:
1. The act is done by force or against the will of the other participant, whether or not the other participant is the person's spouse or is cohabiting with the person.
2. The act is between persons who are not at the time cohabiting as husband and wife and if any of the following are true:
a. The other participant is suffering from a mental defect or incapacity which precludes giving consent.
b. The other participant is twelve or thirteen years of age.
c. The other participant is fourteen or fifteen years of age and any of the following are true:
(1) The person is a member of the same household as the other participant.
(2) The person is related to the other participant by blood or affinity to the fourth degree.
(3) The person is in a position of authority over the other participant and uses that authority to coerce the other participant to submit.
(4) The person is five or more years older than the other participant.