Rate of Twin Births At A Global High
The first comprehensive global survey of twinning has reported an enormous increase in the number of twin births around the world, but appears to be plateauing.
One main reason for the increase is that, due to IVF and other fertility services being more readily available, the number of non-identical twin births is increasing. This is due to practices such as hormone stimulation releasing multiple ova, as well as the now discouraged practice of releasing multiple embryos into the womb in IVF. A systematic review also found that with IVF, letting embryos mature before implantation is also linked to increased odds of monozygotic twins. as well as women becoming pregnant later in life – age increases the likelihood of having natural, non-identical twins, peaking at age 35 to 39.
However, instead of continuing to climb, there are signs that twin births have reached a maximum.
“The trends are really quite striking,” said Christiaan Monden, a professor of sociology and demography at Oxford University. “Over the past 40 to 50 years we’ve seen a strong increase in twinning rates in rich, developed countries, and that has led to more twins in both a relative and an absolute sense than we’ve seen ever before.”
The researchers analysed twinning rates from 2010 to 2015 in 165 countries, which covered 99% of the world’s population. In 112 of those countries, they examined further birth records for 1980 to 1985.
Although Africa is still the leading continent for twin births, other regions are catching up. The researchers found that, since the 1980s, twinning rates have risen from 9 to 12 per 1000 births, with the greatest rise in more developed regions such as America (71%), Europe (60%) and Asia (32%).
In the UK, twinning rates rose about 62% but are thought to have fallen since the launch of a campaign to reduce multiple births in 2007.
Raj Mathur, the chair of the British Fertility Society and a consultant gynaecologist at St Mary’s Hospital, said: “It doesn’t surprise us that twinning rates have increased because the availability of assisted reproduction has increased and also because women are slightly older when they have their first children, and both those things will increase the twin rate.[…]
“I think we’ve reached a peak in terms of twinning rates from medical interventions, certainly in the developed world, but the spread of IVF in Africa and South America is still rather limited on a per capita basis, and there are vast numbers of sub-fertile people in Africa particularly who don’t have access to IVF.
Dr Mathur added a note of caution about IVF, as twins have more risks such as lower birth weights and higher still birth and infant mortality rates
“The challenge will be how to spread IVF to them without also giving them higher twin rates. The majority of twin babies are absolutely fine, but there is no doubt that a twin pregnancy carries greater risks for the mother and the baby, so when we can avoid it we should avoid it. The principle we follow is neatly summed up by the phrase ‘one at a time’,” Mathur said.
Source: The Guardian
