Global twin birth rates may have peaked as one in 42 are born a twin, which is likely due to the accessibility of IVF and other fertility treatments.
European researchers examined twinning rates during 2010-2015 across 165 countries, showing a global surge since the 1980s from nine to 12 twin births per 1000 deliveries. This is primarily driven by increases in twin birth rates in Europe (+58 percent), Asia (+32 percent) and North America (+71 percent) where access to fertility treatments, such as IVF, has significantly improved over the same 30-year period.
'The relative and absolute numbers of twins in the world are higher than they have ever been since the mid-20th century and this is likely to be an all-time high.' said Professor Christiaan Monden of the University of Oxford and first author of the study. 'This is important as twin deliveries are associated with higher death rates among babies and children and more complications for mothers and children during pregnancy'.
In the paper, published in Human Reproduction, 74 of 112 countries which also had data available from 1980-1985 showed at least a ten percent increase in twinning rates. Among this group was the UK, however, the actual frequency of twin births is thought to have fallen since 2007 when the Human Fertilisation and Embryology Authority (HFEA) launched their 'One at a Time' campaign. IVF is associated with a higher likelihood of multiple or twin births, which the HFEA aims to reduce to avoid health complications such as postnatal depression or low birth weight.
Previous research by the authors demonstrated that IVF is among fertility treatments that can have three times the effect on twin birth rates as delayed childrearing age.
According to the Guardian, chair of the British Fertility Society and consultant gynaecologist at St Mary's Hospital in Manchester, Dr Raj Mathur, commented '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'.
The researchers aim to update their findings with data from the early 2020s to establish whether twin births have truly plateaued. As IVF availability continues to expand into regions with already high twinning rates, such as West and Central Africa, this will be essential for forecasting the demand on health services.