**Core Concept**
Hellin's law is a statistical principle used to estimate the likelihood of twin pregnancies in the general population. This law is based on the observation that the frequency of twin births is inversely proportional to the square of the population size. It is a useful tool for obstetricians to estimate the risk of multiple gestations.

**Why the Correct Answer is Right**
Hellin's law states that the chances of twin births are approximately 1 in 80. This is because the law takes into account the fact that the likelihood of twin births decreases as the population size increases. In other words, as the number of pregnant women in a population grows, the number of twin births decreases. This is because the chances of two eggs being released at the same time and fertilized by two different sperm are relatively low. The law is a useful tool for clinicians to estimate the risk of multiple gestations and to counsel patients appropriately.

**Why Each Wrong Option is Incorrect**
**Option A:** 1 in 60 is too high and does not accurately reflect the estimated risk of twin births according to Hellin's law.
**Option B:** 1 in 70 is also too high and does not accurately reflect the estimated risk of twin births according to Hellin's law.
**Option D:** 1 in 90 is too low and does not accurately reflect the estimated risk of twin births according to Hellin's law.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that Hellin's law is a statistical estimate and may not apply to individual cases. Women who have a family history of twins or who are over 35 years old may have a higher risk of multiple gestations, regardless of the estimated risk according to Hellin's law.

**✓ Correct Answer: C. 1 in 80**