**Core Concept**
The question is testing the understanding of the relationship between middle ear function and impedance audiometry. Impedance audiometry is a test used to assess the function of the middle ear system, including the tympanic membrane (eardrum), ossicles, and the middle ear muscles. The test measures the mobility of the eardrum and the conduction of sound through the middle ear.

**Why the Correct Answer is Right**
During pregnancy, there is an increase in blood volume and fluid retention, leading to a decrease in the mobility of the eardrum. This is known as middle ear barotrauma or Eustachian tube dysfunction. The graph that would be expected in this scenario is a type B tympanogram, which indicates a non-compliant middle ear system. The tympanogram would show a flat or depressed peak, indicating that the eardrum is not moving normally due to increased fluid and decreased mobility.

**Why Each Wrong Option is Incorrect**
* **Option A:** This would be a type A tympanogram, indicating a normal middle ear system with good mobility of the eardrum. This is not consistent with the patient's symptoms.
* **Option B:** This would be a type C tympanogram, indicating a tympanic membrane that is fixed in place, often due to otosclerosis. This is not consistent with the patient's symptoms of worsening hearing loss during pregnancy.
* **Option D:** This is not a valid option for a tympanogram type.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that middle ear barotrauma can occur during pregnancy due to increased fluid retention and decreased mobility of the eardrum. This can lead to conductive hearing loss, which can be temporary or permanent if left untreated.

**Correct Answer:** C.