**Core Concept**
A post coital bleed is a symptom that warrants investigation for potential underlying causes such as cervical or vaginal pathology. The absence of growth on per speculum examination suggests that the bleeding may not be due to a visible lesion, making further evaluation necessary.

**Why the Correct Answer is Right**
In this scenario, the next step would be to perform a **cervical biopsy**. This is because post coital bleeding can be a sign of cervical cancer or other precancerous lesions, which may not be visible on routine examination. A cervical biopsy allows for histopathological examination of the cervical tissue to rule out any malignancy. The biopsy should be taken from the posterior lip of the cervix, as this is the most common site for cervical neoplasms.

**Why Each Wrong Option is Incorrect**
**Option A:** Endocervical curettage (ECC) may be performed in cases of abnormal Pap smear results or in the presence of cervical lesions, but it is not the next step in this scenario where no growth is seen.

**Option B:** Colposcopy with biopsy is useful in evaluating visible lesions or abnormal Pap smear results, but it may not be necessary if no growth is visible.

**Option C:** Cone biopsy is typically performed in cases of high-grade cervical dysplasia or when a definitive diagnosis cannot be made after cervical biopsy.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that post coital bleeding is a red flag symptom that warrants further evaluation, even if no growth is visible on routine examination. A cervical biopsy is essential to rule out underlying malignancy.

**Correct Answer: A. Cervical biopsy.**