During the second trimester, ultrasound can be used to note markers for increased likelihood of Down syndrome, but not all markers are created equal. According to a study published in the journal Ultrasound in Obstetrics & Gynecology, doctors should look for a specific set of markers associated with the highest risk.
Prenatal screening for Down syndrome is one of a series of tests offered to pregnant women. The test is not mandatory and some women choose not to have the test. Women who choose to be screened for Down syndrome are placed in a risk category based on age. Women at high risk may be given an ultrasound to ascertain if fetal development shows signs of Down syndrome characteristics. Development of the nose, brain, kidney, heart and bowels are noted during the ultrasound, as are bone growth and neck thickness. While all characteristics should be noted in the patient’s medical files, some Down syndrome characteristics post a higher risk than others.
Researchers pulled medical data from 48 studies spanning 1995 to 2012. Research revealed that fetuses exhibited just one marker is not necessarily at increased risk for Down syndrome, unless the marker was associated with significant increased risk based on live birth statistics. For instance, when neck thickness, dilated ventricles of the brain or arterial abnormalities of the upper extremities was noted the fetus has up to a four-fold greater risk of having Down syndrome. A missing or smaller than normal nose increases the risk to six-fold. It was also noted, alternatively, that lack of any Down syndrome characteristics decreased risk seven times.
Down syndrome is caused by a chromosomal anomaly. Early detection can help parents prepare for the possibility of having an infant with Down syndrome, but there is no treatment or cure for the condition. Ultrasound detection and chromosome tests are performed strictly for informational purposes and to detect possible physical anomalies prior to delivery.
Source: M. Agathokleous, P. Chaveeva, L. C. Y. Poon, P. Kosinski, K. H. Nicolaides. Meta-analysis of second-trimester markers for trisomy 21. Ultrasound in Obstetrics & Gynecology 24 Jan 2013; DOI: 10.1002/uog.12364.