This infection is one of the most common causes of death worldwide
More twin babies are being born today than at any other time since records began. In fact, approximately 1.6 million twin pairs are born around the world every year. Reasons for this twin boom include advancements in medical reproductive technologies. But it can also be explained by the fact that more women are having children later in life. Now you may be asking: how does delayed parenthood increase the chances of a multiple birth?
Click through the following gallery for the answer to this intriguing question, and find out what other factors increase the odds of having twins.
In 2024, the town of Inverclyde, Scotland, saw 10 sets of twins (six pictured) start elementary school all at once.
In the same month in the United States, 23 pairs of twins said goodbye to a Needham, Massachusetts, middle school as they finished their eighth grade studies. Earlier still in 2017, seven sets of twin siblings graduated from Portland High School in Maine.
The past 30 years or so has seen an increase in the instance of twins, with 3.1% of births being twins in 2021, compared with 1.9% in 1980.
In fact, each year approximately 1.6 million twin pairs are born around the world. Back in the 1980s, this figure was a third lower.
This is despite the fact that, globally, mothers are having fewer children. Yet while the birthrate appears to be in decline, the number of twins and triplets being born today is higher than ever before.
There are several reasons why this may be the case. Primarily, it's because more people are seeking help with getting pregnant.
According to a report published by Ohio State University, medical reproductive technologies like in vitro fertilization (IVF) are one of the factors contributing to a rise in twin births.
Indeed, fertility treatments, including drugs to increase ovulation and techniques like IVF, increase the chances of having multiple babies.
According to the UK's Human Fertilisation & Embryology Authority (HFEA), more than 1.3 million IVF cycles and 260,000 donor insemination cycles have been carried out in Great Britain, leading to the birth of 390,000 babies.
Interestingly, other factors believed to increase the odds of conceiving twins include older-age pregnancy.
A 2022 report by the Associated Press (AP) revealed that the median age of US women giving birth is from 27 to 30, the highest on record.
In the United Kingdom, a survey conducted by the Office for National Statistics (ONS) found that, on average, most women in Britain now have their first child from the age of 32 onwards. In 1960, the median age was 26.
As a woman gets older, the difficulty of getting pregnant and the percentage of miscarriages also increase.
But they are also likely to give birth to twins, even without using reproductive technologies like IVF. How is this so?
Women in their thirties have a greater chance of conceiving fraternal twins as a result of an evolutionary response to combat declining embryo viability.
In fact, a woman at 35 years old is four times more likely to have fraternal twins—a result from the fertilization of two separate eggs with two different sperm during the same pregnancy.
This occurs because it's more probable she'll release more than one egg during ovulation.
The likelihood of conceiving twins is a complex trait and one that can also be decided by family history. Twins tend to be more common in certain families, a factor linked to the parent whose body releases the egg.
For example, there may be an underlying genetic component that predisposes someone to release more than one egg at a time, ergo increasing the chance of having twins.
Race also plays a role in the twin boom. According to data published in 2024 by Statista, in the United States, non-Hispanic Black women currently have higher rates of twin births than any other ethnicity or race with 41.4 per 1,000 live births being twins.
Conversely, most statistics show that currently the lowest rate of twins is in the Asian population. Experts are at odds as to how much of a role ethnicity plays, but it may be due to dietary factors more than genetics.
It's worth pointing out the difference between fraternal twins and identical twins. As mentioned earlier, fraternal twins form from two eggs that are fertilized by two sperm.
Identical twins form when one fertilized egg splits and develops two babies.
Hyperovulation, also known as superovulation, is a rare condition that occurs when a woman releases more than one egg during a menstrual cycle.
This phenomenon is typically caused by fertility treatments or hormonal imbalances.
Hyperovulation can increase the odds of conceiving twins or multiple pregnancies, for example triplets. Rarer still is the birth of four twins, or quadruplets. In extreme cases, quintuplets (five) and the multiple births of six twins have been recorded. In Morocco in 2021, a woman successfully gave birth to the world's first nonuplets, nine babies born at the same time and all apparently in good health.
In the wider world, twinning rates are estimated to increase in most low-income countries by 2050 and even more by 2100, according to the journal Human Reproduction.
Many sub-Saharan African and South Asian countries are undergoing, and projected to further experience, the shift of maternal age at birth to older ages, the report notes. Presently, however, it's unknown how the changes in maternal age distribution are associated with the changes in twinning rates at the population level in these low-income nations.
One of the highest rates of twinning in the world is to be found among a particular Indigenous group in Africa called the Yoruba. Interestingly, experts at Ohio State University cite diet as one possible reason the twinning rate is so high among the Yoruba. It's rich in a specific kind of yam that contains a phytoestrogen, or plant-like estrogen, that may increase the rate of multiple births.
But it's in the Ivory Coast where the highest rate of twinning has been recorded. According to a study of data from 135 countries published by the University of Oxford in 2020, the African country registered a rate of 24.9 twins for every 1,000 deliveries in the period of 2010–2015, a fact confirmed by Guinness World Records.
Sources: (Geographical) (The Conversation) (Guinness World Records) (Ohio State University) (HFEA) (AP) (ONS) (Statista) (Parents) (Oxford Academic) (BBC)
Seeing double! Why are more twins being born?
What increases the odds of having twins?
HEALTH Children
More twin babies are being born today than at any other time since records began. In fact, approximately 1.6 million twin pairs are born around the world every year. Reasons for this twin boom include advancements in medical reproductive technologies. But it can also be explained by the fact that more women are having children later in life. Now you may be asking: how does delayed parenthood increase the chances of a multiple birth?
Click through the following gallery for the answer to this intriguing question, and find out what other factors increase the odds of having twins.