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Twin birth rate on the rise due to assisted conception

15 February 2016
Appeared in BioNews 839

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, according to a recent study.

In England and Wales, the rate increased from 9.9 twins per 1000 births in 1975 to 16.1 in 2011, while similar increases were reported for the US (from 9.5 to 16.9), Germany (from 9.2 to 17.2) and France (from 9.3 to 17.4).

The increase is due to a higher incidence of fraternal twins, which arise when two eggs are released at the same time and fertilised by two different sperm. This event occurs more frequently in older women, and the authors think this partially accounts for the recent increase in twin births in developed countries.

The other reason for the increase, according to the study, is a 'sharp rise' in fertility treatments. In the early years of IVF it was commonplace to implant three or more embryos, resulting in high multiple birth rates by the year 2000. Ovarian stimulation by hormone treatments also increases the likelihood of two eggs being released at the same time.

'We're not sure if the rate will continue to rise, but the data is increasingly seen as a public health crisis', Gilles Pison, study co-author from the French National Institute for Demographic Studies, told the Independent.

In the report, published in Population and Development Review, the authors drew attention to the dangers associated with twin births compared to singletons: '[Twin babies] have lower birth weight, more complications at birth, and are more often born premature – all of which are associated with many long-term health problems.'

Multiple births also pose a risk to the mother, with an increased risk of health issues such as pre-eclampsia and postpartum depression.

The authors estimate the effect of fertility treatments on increased twinning rates to be on average 'about three times greater than the effect of delayed childbearing'. To address the high percentages of multiple births following medically assisted reproduction, many countries have introduced guidelines encouraging the transfer of fewer embryos following IVF.

Reflecting these changing practices, researchers observed a decline in multiple births in recent years in around a quarter of the countries studied. In the majority of countries however, including England and Wales, twin births have continued to rise.

The authors think this increase may reflect the increasing number of women turning to fertility treatments and the continuing trend toward later motherhood.

'The number of treatments continues to increase, and the average age of women undergoing these treatments is rising,' the team write.

They suggest that better data should be maintained on the age and nationalities of women having twin births in order to keep track of the impact of policies and practices around medically assisted reproduction.

7 October 2019 - by Dr Jennifer Frosch 
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 reports...
11 February 2019 - by Jakki Magowan 
Women who have fertility treatments have a slightly higher risk of severe complications during pregnancy and delivery than those not undergoing treatment...
3 May 2016 - by Anneesa Amjad 
A study has identified two gene variants that increase the likelihood of a woman having twins and could explain why twins appears to run in families...
22 February 2016 - by Ryan Ross 
The use of IVF technologies could be storing up future health problems for children born through the technique, according to an evolutionary biologist...
11 January 2016 - by Dr Katie Howe 
Children conceived using IVF and other fertility treatments are at no greater risk of developmental delays than children conceived naturally, according to a large US study...
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....
16 December 2013 - by Dr Jess Buxton 
Twins have long been an endless source of fascination to their family, friends and society, and also to scientists. This year, the topics of twins in genetics and twins in fertility treatment formed the two halves of Progress Educational Trust's annual conference...
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...
25 November 2013 - by Ari Haque 
A report from the Office for National Statistics (ONS) shows that the number of multiple births among women over 45 has increased by 23 percent in the past year. The increase is thought to be in part due to more older women using IVF treatment to conceive...
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