During pregnancy, what principal diagnosis code should be assigned for an HIV-related illness?

The selection of O98.7- as the principal diagnosis code is justified because this code is specifically used to indicate that the patient is pregnant and has an HIV-related illness. In ICD-10-CM coding for pregnancy, it is crucial to prioritize the maternal condition that impacts the pregnancy, hence the use of O98.7- which identifies the condition as occurring in a pregnant patient.

Following this, B20 is assigned to denote the actual diagnosis of HIV disease. This sequence accurately captures the relevant information regarding the patient's health status during pregnancy. This coding approach is aligned with existing guidelines which dictate that the principal diagnosis should reflect the condition directly impacting the pregnancy, thus correctly documenting both the pregnancy and the HIV-related illness for complete and accurate medical records.

In contrast, other options may lead to improper coding practices, such as prioritizing the HIV diagnosis without recognizing the relevant pregnancy context, or using less specific codes which do not adequately convey the patient's overall health picture during pregnancy.