Did you know that Spain is the third country with the most twin births in the world ? The country also leads the number of twins in Europe with an average rate of around 4%. Among other reasons, it is due to the growing use of assisted reproduction techniques. Unlike other countries, Spanish law allows up to three embryos to be transferred in assisted fertilization techniques, which considerably increases the chances of having a twin pregnancy.

Although in recent years, many clinics have opted to transfer a single embryo in each attempt, it is estimated that since the introduction of assisted reproduction techniques the number of twin pregnancies in Spain has tripled, or what is the same, have increased by 287%. However, assisted reproduction techniques are not the only “culprits”, there are other factors that can increase a woman’s chances of having twins or twins.

Factors that increase your chances of having twins

1. The age of the mother

As the mother’s age increases her fertility decreases, but instead, her chances of having a multiple pregnancy increase. This was confirmed by a study carried out at the Vrije University Medical Center in Amsterdam, which found that between the ages of 30 and 34, the chances of having twins increase to 4% , while in the following five years they rise to 5% . and from the age of 40 they shoot up. Among other factors, it is due to the fact that as age increases, hormones stimulate ovulation, and several ovules can be generated in each menstrual cycle.

2. Mother’s weight

Having a BMI equal to or greater than 30 increases the chances of having multiple ovulation and, with it, a multiple pregnancy. This was corroborated by a study carried out at the National Institute of Child Health and Human Development in the United States, in which the self-reported body mass index of women before becoming pregnant was related to the prevalence of multiple gestations. The results revealed that those women who were overweight before conceiving were more likely to have twins compared to those who were of normal weight.

3. Size of the mother

Taller women are also more likely to have multiple pregnancies, as revealed by research conducted at the US National Institute of Child Health and Human Development. That probability increases considerably in the case of women who are very tall and who are also overweight. The causes are not entirely clear, but experts believe that it may be because growth hormone stimulates multiple ovulation, increasing the chances of having a twin pregnancy.

4. History of twin pregnancy

Having had a previous twin pregnancy increases the chances of developing a new multiple gestation. Scientists believe that it is due to a natural predisposition of the mother to have multiple ovulation, which in turn increases the chances of twin fertilization. In the case of a first pregnancy of twins through assisted reproduction, in the second pregnancy the statistics are practically the same.

5. Genetic inheritance

Having twins in the family doubles the chances of having a multiple pregnancy, according to a study conducted at the Free University of Amsterdam. The chances are greater if it is the maternal family, but it should also be taken into account that although men do not manifest this inheritance because they do not ovulate, they do transmit this probability to their daughters. Therefore, if there are fraternal twins in the mother’s paternal family, the possibility of having inherited these genes and having a multiple pregnancy is quite high.

Improper use of the contraceptive pill is also known to increase the chances of a multiple pregnancy. This is because after stopping the pills , there is usually a rebound effect that stimulates ovulation and increases the possibility of producing more than one egg per period. If right at that moment, the woman becomes pregnant, she has a greater probability of having a pregnancy of twins or twins.

Likewise, it has been found that race can influence the development of a multiple pregnancy. Asian women are the least likely to carry twins or twins to term, while black women are the most likely, as revealed by a study by the United States Department of Health and Human Services. in conjunction with other institutions.

The real chances of having twins

Although they are often used interchangeably, there are actually important differences between twins and twins. Fraternal twins develop from two different eggs, each fertilized by a sperm, giving rise to two independent zygotes. On the other hand, twins are formed from the same egg that, after being fertilized by a single sperm, divides, giving rise to two embryos.

In practice, it is very easy to distinguish fraternal twins from twins since while the latter share the same genetic information and have identical characteristics, the fraternal twins do not have many common traits since they do not share the same genetic information. A distinction that you must take into account when assessing your chances of having a twin or twin pregnancy since they vary.

Basically, it is estimated that the chances of a pregnant woman having twins naturally are 1.1%, that is, approximately 1 in 90 women has twins. In contrast, the chances of having a twin pregnancy are almost three times lower, 0.4%, this means that only 1 in 250 pregnancies is twin.

However, in the case of in vitro fertilization , although the chances of having twins remain unchanged since it is usually due to an “accident” during fertilization, the chances of having a twin rise considerably to 30-35%. A risk that increases when the use of drugs to stimulate the production of eggs is added to the transmission of more than one embryo, which increases the chances of a multiple pregnancy.

  • Europa Press (2015) Spain is the third country in the world with births of twins. In: The Voice of Galicia .
  • Spanish Fertility Society (-) Multiple pregnancy. Spanish Fertility Society .
  • Beemsterboer, S. et. Al. (2006) The paradox of declining fertility but increasing twinning rates with advancing maternal age. The Human Reproduction , 21(6): 1531–1532.
  • Reddy, U. et. Al. (2005) Relationship of maternal body mass index and height to twinning. Obstetrics & Gynecology , 105(3): 593-597.
  • Hoekstra, Ch. et. Al. (2008) Dizygotic twinning. The Human Reproduction Updates , 14(1): 37-47.
  • Martin, J. et. Al. (2015) Births: Final Data for 2013. National Vital Statistics Reports , 64(1): 1-65.
  • Torres, V. (2016) Spain, the kingdom of the twins. In: The Country .