**Core Concept**
The routine vaccination in pregnancy is aimed at preventing complications such as preterm labor and fetal distress. Tetanus toxoid is a crucial vaccine given during pregnancy to protect the mother and the fetus from tetanus infection.

**Why the Correct Answer is Right**
Tetanus toxoid is administered during pregnancy as part of the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine. This vaccine is essential for pregnant women, particularly those who have not received the vaccine in the past 10 years, to prevent neonatal tetanus and maternal tetanus. The Tdap vaccine protects the mother from tetanus infection, which can be transmitted to the fetus through the placenta, and also provides passive immunity to the newborn.

**Why Each Wrong Option is Incorrect**
**Option A:** Influenza vaccine is recommended for pregnant women, especially during the flu season, but it is not a routine vaccine given during pregnancy.
**Option B:** Oral polio vaccine (OPV) is not recommended for pregnant women due to the theoretical risk of vaccine-associated poliomyelitis.
**Option D:** Rabies vaccine is not routinely given during pregnancy, except in high-risk situations such as exposure to an infected animal.

**Clinical Pearl / High-Yield Fact**
Pregnant women should receive the Tdap vaccine between 27 and 36 weeks of gestation, regardless of their vaccination history, to provide optimal protection against tetanus and pertussis.

**✓ Correct Answer: C. Tetanus**