**Core Concept**
The management of tuberculosis (TB) in pregnancy requires careful consideration of the risks and benefits of antitubercular therapy (ATT) to both the mother and the fetus. Category I ATT refers to the standard treatment regimen for pulmonary TB, which includes isoniazid, rifampicin, pyrazinamide, and ethambutol.

**Why the Correct Answer is Right**
The World Health Organization (WHO) recommends starting Category I ATT in the first trimester of pregnancy for sputum-positive TB, as the benefits of treatment outweigh the risks. This approach has been shown to reduce maternal mortality and improve fetal outcomes. Category I ATT is effective in treating pulmonary TB, and the regimen used does not have a significant impact on fetal development. The first trimester is a critical period for fetal organogenesis, and delaying treatment may lead to worsening of maternal health and increased risk of complications.

**Why Each Wrong Option is Incorrect**
**Option A:** Waiting for the second trimester to start ATT may lead to worsening of maternal health and increased risk of complications, including TB-related maternal mortality. Delaying treatment also increases the risk of vertical transmission of TB to the fetus.
**Option C:** Category II ATT is typically reserved for patients with severe TB or those who are unable to tolerate Category I ATT. Starting Category II ATT in the first trimester may not provide adequate treatment and may increase the risk of treatment failure.
**Option D:** Category III ATT is not a standard treatment regimen for pulmonary TB, and starting it in the second trimester may delay treatment and increase the risk of complications.

**Clinical Pearl / High-Yield Fact**
The WHO recommends that all pregnant women with sputum-positive TB be started on Category I ATT in the first trimester, as the benefits of treatment outweigh the risks. This approach has been shown to reduce maternal mortality and improve fetal outcomes.

**✓ Correct Answer: B. Start Category I ATT in first trimester**