Out of 33 pregnancies, 1 woman gives birth to twins. This shows a 74% increase in twin births over the last 20 years, in part due to the improvement and increased use of infertility treatments.
The most common form of twins is fraternal twins. This is conceived when 2 eggs are released during ovulation. Boy-girl fraternal twins consist of around 40% of double births. The next most common is fraternal girls followed by fraternal boys.