A BMI of 25 or higher is termed overweight, while 30 and above is considered obese.
A Danish study has found that women with a body mass index (BMI) of 30 or higher are more likely to give birth to twins than normal-weight or underweight women.
However, the twins of obese women were slightly more likely to be opposite-sex than same-sex twins.
Why do obese women give birth to twins?
A study by Olga Basso, a research associate professor at the University of Arhus, and her team found that most twin births resulted in fraternal offspring, which are the result of two eggs being fertilized.
Factors believed to be behind twin births include maternal age, family history, race, and possibly height and weight.
Additional research by William Bates of Vanderbilt University agrees with this Olga. He suggests that hormonal differences between normal-weight and overweight women may be the cause of twin birth differences.
Overweight women have higher levels of luteinizing hormone, which triggers ovulation, allowing them to release two eggs at once during a monthly cycle.
However, it is not advisable for women to gain weight just because they want twins.