The idea that playing classical music, particularly compositions by Mozart, to a fetus can make a baby smarter is often referred to as the "Mozart effect." This concept suggests that exposure to classical music might enhance a baby's intelligence, particularly in spatial reasoning. However, the evidence supporting this claim is mixed and not as definitive as often portrayed in popular media.

### Key Points on the Mozart Effect and Prenatal Music Exposure

1. **Origin of the Mozart Effect**:
   - The term originated from a 1993 study by Rauscher, Shaw, and Ky that suggested listening to Mozart's music might temporarily improve spatial reasoning in college students. The findings were misinterpreted and overgeneralized to suggest broader intelligence benefits for infants and even fetuses.

2. **Research on Prenatal Music Exposure**:
   - **Mixed Results**: Some studies suggest that playing music to a fetus can lead to changes in fetal heart rate and movement, indicating that the fetus can hear and respond to music. However, there is no conclusive evidence that this leads to long-term intellectual benefits.
   - **Brain Development**: While music can stimulate a baby's auditory and sensory systems, there is no strong evidence to support that it specifically enhances cognitive development or makes babies smarter.

3. **Potential Benefits**:
   - **Soothing Effects**: Music can have a calming effect on both the mother and the fetus, potentially reducing stress and creating a positive environment for fetal development.
   - **Bonding**: Listening to music can be a bonding experience for parents and their unborn baby.

4. **Criticism and Limitations**:
   - **No Proven Cognitive Boost**: Many researchers argue that there is no solid scientific foundation to the claim that prenatal exposure to music boosts a baby's IQ or overall intelligence.
   - **Short-Term Effects**: Some of the observed benefits, like temporary increases in spatial-temporal reasoning, do not have lasting impacts on cognitive development.

5. **Overall Recommendation**:
   - While playing music to a fetus is not harmful and can be a pleasant experience, it should not be relied upon as a method to boost intelligence. Focus on overall well-being, stress reduction, and healthy prenatal practices for the best developmental outcomes.

### Conclusion

Playing classical music to a fetus is unlikely to make your baby smarter in the long term, but it can be a beneficial and enjoyable activity for both mother and baby. The key to healthy brain development lies more in overall prenatal care, nutrition, and a stress-free environment rather than in specific activities like listening to classical music.