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Ultrasound misses many heart defects in foetuses
13 March 2014
Over six in every ten serious heart defects in foetuses go undetected in the ultrasound scans given to all pregnant women. According to research at Linköping University in Sweden, one reason why malformations are not found is obesity in the expectant mother.
Each year around 2,000 children are born in Sweden with serious malformations, of which almost half are heart defects. Discovering these during the first stage of pregnancy is a major challenge for prenatal healthcare.
“The lives of children born with serious heart defects are in constant danger; some of them need immediate operations or medical treatment. If these defects are detected during the pregnancy the babies can be born in Lund or Gothenburg where the hospital has facilities for child heart surgery,” explains Eric Hildebrand, senior physician at the Linköping University Hospital Women’s Clinic and also a graduate student in obstetrics and gynaecology at Linköping University.
The basis of his study is an examination of over 21,000 ultrasound scans in the south-east healthcare region in Sweden, covering the counties of Jönköping, Kalmar and Östergötland. In this region all expectant mothers are offered two ultrasound scans, the first in weeks 11-14, and the second in weeks 18-20. In the first scan the midwife dates the pregnancy, looks for the possibility of twins and carries out a general examination of the anatomy of the embryo. In the second scan the organs are screened for malformations.
In the examination the results of the two scans are compared. Not surprisingly, considerably fewer malformations are detected in the first scan. It was particularly difficult to find heart defects. During the eleventh to the fourteenth weeks no defects at all were found, but in the eighteenth to twentieth week, 37% of serious defects were discovered.
One reason for missing malformations is that the ultrasound image is affected by the body of the mother. For example diagnosis is made more difficult by obesity–a BMI over 30–which is the case for 13% of the mothers.
“Subcutaneous fat detracts from the quality of the image, making it more difficult for us to see malformations,” says Dr Hildebrand.
The statistics also show that obesity itself increases the risk of conditions like spina bifida, although the increased risk for the individual is small. That makes it extra important to be able to offer good embryo diagnostics for the expectant mother.
In the case of chromosome abnormalities, a thorough examination of the national medical birth register of children born between 1995 and 2010 showed that one in 700 children was born with Downs syndrome. A certain connection with obesity was also seen.
Dr Hildebrand puts forward a couple of important measures for a more trustworthy embryo diagnostic that came out of the in the studies:
- The methods of detecting heart defects need to be improved. One way is to give midwives additional education and training in interpreting heart images, including with what is known as colour Doppler for blood flow in the heart.
- The best diagnostic tool for Downs Syndrome is the CUB, or Combined Ultrasound and Biochemical screening test, which works just as well regardless of whether the mother is obese or not.
Thesis: Prenatal diagnosis of structural malformations and chromosome anomalies. Linköping University Medical Dissertations No. 1387. The thesis will be presented on March 14th 2014.