Today is #BumpDay and we’re celebrating all the twin siblings in the world! The rate of twin births has increased 76 percent since 1980, and will likely keep increasing in the future. That means that 1 in every 30 babies is born a twin. Crazy!

There are actually tons of fascinating facts about twins and their relationships. We did some research and compiled some of the most interesting facts we could find.

Do you know all of these facts about twins?

  • If you have twins, you’re more likely to give birth early. About 60 percent of twins are born prematurely. Most twin pregnancies last just 35 weeks. For this reason, you’ll get extra monitoring from your doctor throughout your pregnancy.
  • There are more than just two types of twins. Most people know that twins can be either fraternal or identical. However, twins can also be conjoined or “mirror image twins,” which happens when the egg splits more than one week after conception. Mirror image twins can have the same birthmarks on opposite sides, or one will be left-handed and the other will be right-handed.
  • Twins can develop their own language. Idioglossia or cryptophasia refers to when twins mimic the babbles of each other instead of their parents. About 40% of twins develop this special “language,” but it doesn’t affect their ability to learn how to speak!
  • The bonding starts before birth. 3D ultrasound images have shown images of twins bonding in utero. The fetuses reached for each other intentionally or caressed each other as early as 18 weeks!
  • Even identical twins have differences. Even if your twins look exactly alike, there is one part of the body that will never be identical. Even though identical twins share the same DNA, fingerprints are not generated solely from DNA. During weeks six through 13 of pregnancy, as the babies start to move, they each touch the amniotic sac and unique ridges and lines are formed on each twin’s hand that result in different fingerprints.
  • Massachusetts has the highest rate of twin births. For every 100 births, 4.5 of them will be twins. Connecticut and New Jersey follow as having the next highest rate of twins, while New Mexico has the lowest rate.
  • Tall women are more likely to give birth to twins. Taller women have more of the insulin-like growth factor protein (IGF). IGF increases the sensitivity of the ovaries to the follicle stimulating hormone, thereby increasing ovulation.

Aside from sharing a very strong bond, twins have some pretty amazing facts. If you’re expecting twins, make sure you follow these important steps during your pregnancy.