[Abstract below]
German scientists found the rate of twin births in areas with high environmental pollution were double that of other areas.
The rate was highest among women living near a toxic waste incinerator, the authors say in the Occupational and Environmental Medicine journal.
They recommend further research to find out why this might be.
The University of Hamburg team compared twin birth rates among mothers living near an incinerator in Hesse and mothers living in two other regions of Germany.
Proximity to pollution
One region was 20km north of the incinerator and the other was a non-industrial area much further away.
In areas where people lived close to the incinerator or other heavy industries, the twin birth rate was about twice as high as other areas.
In Hesse, 5.3% of mothers had twins compared to 1.6% 20km away and 2.3% in the non-industrial area.
Dr Nadia Obi-Osius and colleagues then checked the trend was not due to fertility treatment, which is known to increase the likelihood of multiple births.
Fertility treatment was more common in the non-polluted areas than in the polluted regions, and the twinning rate was no higher among women undergoing fertility treatment.
In the UK, the proportion of multiple births has increased by 20% in the last 10 years, according to the Office for National Statistics.
In 2002, the multiple birth rate was 15 per 1,000 women giving birth, compared with 12.5 in 1992.
In Scotland in the early 1980s women living near to incinerators showed higher twinning rates.
Belgian researchers have found similar trends.
But Swedish scientists found no increase in twinning rate around 14 incinerator plants.
Possible mechanism
Given the increased health risks of multiple births, such as low birth weight, the researchers say further research is needed to find out why this might occur.
Professor Nick Fisk, professor of Obstetrics and Gynaecology at Queen Charlottes' Hospital in London, said there were a couple of possible mechanisms behind the trend.
He said it might be that the women in the study were at lower risk of miscarriage, but he thought that was unlikely.
He said it was possible that toxic waste had an effect on female hormones.
"It is possible that something in the toxic waste suppresses oestrogen levels in women. Therefore, they have higher gonadotrophin levels - they are the hormones that kick start the egg forming," he explained.
If you have higher gonadotrophin levels you are more likely to make more eggs that could become fertilised at the same time, resulting in non-identical twins.
"There is a plausible mechanism but that would only apply to non-identical twins."
"It's very different from identical twins which occur when the fertilised egg splits very early on," he said.
source: http://news.bbc.co.uk/go/pr/fr/-/1/hi/health/3742967.stm 25may04
ABSTRACT
Obi-Osius1, B Misselwitz2, W Karmaus3 and J Witten4
1 Epidemiological Working Group of the Ministry of Environment and Health and
the Institute for Medical Biometry and Epidemiology, University Hospital
Hamburg-Eppendorf, Germany
2 Institute of Quality Assurance of Hesse, Eschborn/Frankfurt, Germany
3 Department of Epidemiology, Michigan State University, East Lansing, USA
4 Ministry of Social Welfare of Hesse, Department of Health, Wiesbaden, Germany
Correspondence to: Dipl. Biol. N Obi-Osius Epidemiological Working Group, Ministry of Environment and Health and the Institute for Medical Biometry and Epidemiology, University Hospital Hamburg-Eppendorf, Winterhuder Weg 29, 22085 Hamburg, Germany; osius@uke.uni-hamburg.de
Aims: To investigate whether twinning occurs more frequently in residents in the vicinity of a toxic waste incinerator (TWI).
Methods: Within a longitudinal environmental study that addressed child health second grade school children and their parents were recruited. The proportion of twinning in the TWI region was compared with two comparison areas. In a second confirmatory investigation, birth records for the years 1994–97 from the Hessian Perinatal Survey (HEPS) were accessed to determine whether the incidence of twinning was higher in regions around the TWI compared to adjacent reference areas.
Results: In the environmental study, 61.5% of the children and 95% of their mothers participated. In mothers, twinning was 5.3% in the TWI region compared to 1.6% and 2.3% in the comparison regions. The proportion of mothers with fertility assessment/treatment was 5.7%, 8.3%, and 0% respectively. The prevalence of twinning was not significantly higher (4.5%) in mothers with treatment compared to mothers without (3.7%). From the HEPS, data of 20 603 births was analysed. The incidence of twins was significantly higher in areas which surround the TWI and other industries (1.4–1.6 per 100 births) compared to births in reference areas (0.8 per 100).
Conclusions: Twinning rates may be associated with exposure to industrial pollution. Future environmental health studies that consider multiple births as an outcome are warranted. These should also investigate whether the incidence of monozygotic or dizygotic twinning may be associated with industrial pollution.
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Keywords: twin births; multiple births; incinerator; environmental pollution
Abbreviations: DZ, dizygotic twinning; EES, environmental epidemiological study; ESIS, European Study on Infertility and Sterility; HEPS, Hessian Perinatal Survey; MZ, monozygotic twinning; OWC, Odenwald control; PCA, postal code area; RVC, Rhine Valley control; TWI, toxic waste incinerator
source: http://oem.bmjjournals.com/cgi/content/abstract/61/6/482 25may04
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