Obesity of mother means ultrasound can miss heart defects in fetuses

Each year in Europe thousands of children are born 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 hospitals that have facilities for child heart surgery” explains Eric Hildebrand, senior physician at the Linköping University Hospital Women’s Clinic.

But more than six out of every ten serious heart defects in fetuses go undetected in the ultrasound scans given to all pregnant women. According to research recently carried out at Linköping University in Sweden, one reason why malformations are not found is obesity in the expectant mother.

The Swedish group carried out a study involving the 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 at weeks 11-14, and the second at 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 study the results of the two scans were 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 was the case in 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 who suggests two important measures:

•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 color Doppler for blood flow in the heart.

•The best diagnostic tool for Downs Syndrome is the CUB (Combined Ultrasound and Biochemical screening test), which works just as well regardless of whether the mother is obese or not.