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US twin birth rate lowest for a decade - better IVF may be reason

7 October 2019
Appeared in BioNews 1018

The incidence of twin births in the USA has declined to the lowest rate in a decade, the US Centres for Disease Control and Prevention (CDC) reports.

The rate of twin births has decreased by four percent in the last four years, after decades of steady growth since the 1980s. The report emphasises the importance of tracking birth rates due to the higher risk of pregnancy and birth complications affecting twins and their mothers. 

'Though the majority of twins are healthy, the risks are higher for them,' Dr Dmitry Kissin from the CDC told the Wall Street Journal. 'The reduction of twins in this case is a very good thing.' 

Numbers of twin births more than doubled between 1980 (68,339) and 2007 (138,961) – coinciding with the availability of IVF, and the societal trend towards women having their children later in life. As a proportion of total births twins went from 18.9 per thousand to 33.9 – a 67 percent increase. 

However, since 2014, the rate has started dropping by an average of two percent a year. In 2018, the number of twins born (123,536) marked the lowest number reported since 2002.

The report, which used data from the National Vital Statistics System, showed that rates declined more with maternal age: falling by 10 percent for women aged 30 to 34, 12 percent for women aged 35 to 39 and 23 percent for women aged 40 and over. No changes were seen in birth rates among women under 30. Furthermore, twinning rates only fell significantly among white mothers, they remained stable among black and Hispanic women. 

White women over 30 are known to make up the majority of patients at US IVF clinics, and multiple pregnancies have been a common result of fertility treatment, although this may now be changing.

'In vitro fertilisation has improved,' Dr Kevin Doody from the Centre for Assisted Reproduction, Texas, who was not involved in the report told NPR. He called IVF technology 'much more mature' and continued: 

'As we became more aware of the health risks of multiple pregnancy and made efforts to reduce it with IVF, I think that's translated to a reduction in doing things that are risky from an ovulation induction or super-ovulation standpoint.'

Is Twin Childbearing on the Decline? Twin Births in the United States, 2014–2018
US Centers for Disease Control and Prevention |  3 October 2019
Rates of Twin Births in USA Drop After Decades of Increases
Wall Street Journal |  3 October 2019
Twin Birthrate Drops For First Time Since The '80s
npr |  3 October 2019
Twin births in USA now going down, at lowest level in decade
Associated Press |  3 October 2019
15 March 2021 - by Joseph Hamilton 
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 fertility treatments...
10 September 2018 - by Julianna Photopoulos 
Cuts to fertility treatments in the UK are putting women at higher risk of having multiple pregnancies, and increasing costs to the NHS, according to a new report...
15 February 2016 - by Dr Victoria Burchell 
The combination of increased use of fertility treatments and rising maternal age has caused a doubling in the rate of twin births in developed countries over the last 40 years...
26 January 2015 - by Purvi Shah 
A study has shown a decline in the rates of stillbirths and premature deliveries of babies conceived via assisted reproductive technology in four Nordic countries....
9 December 2013 - by Dr Victoria Burchell 
A high level of twin, triplet and other multiple births in the USA may be down to a rise in fertility treatments like ovarian stimulation being used independently of IVF...
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