Ultrasounds during the early weeks of pregnancy may not be effective in detecting fetal brain damage among pregnant women infected by Zika virus, as evidenced by a new report published on March 30.

Researchers in the United States said a Finnish woman — whose identity was not disclosed — went through three ultrasounds during the first weeks of her pregnancy, but the diagnostic technique failed to show signs of brain damage in the fetus.

The unidentified woman was infected with Zika while she was traveling in Mexico, Guatemala and Belize in November last year.

At 19 weeks, another ultrasound scan revealed significant abnormalities. A week later, a more sophisticated magnetic resonance imaging (MRI) scan identified even greater fetal brain damage.

The MRI scan showed that the fetal brain shrunk from a normal head circumference in the 47th percentile at 16 weeks to the 24th percentile at 20 weeks.

The head circumference was not small enough to be diagnosed as microcephaly, but given the extent of brain damage revealed by the MRI, the woman decided to terminate the pregnancy at the 21st week.

Unusual Findings

Report co-author Adre du Plessis says their report suggests that physicians use caution in reassuring patients who have "normal fetal ultrasound examinations" early in their gestation.

In fact, there is an enormous amount of information about this strain of Zika that scientists still do not know about.

Du Plessis said the virus appears to be behaving very differently now than in the past.

"What we do know for sure is if the fetal brain is affected this appears to be a very bad situation," said du Plessis.

Additionally, researchers discovered that the 33-year-old woman still tested positive for Zika 10 weeks after she was infected during this trip — far beyond what experts have believed is the case. Doctors said Zika typically remains in the blood of infected patients for five to seven days.

Neuropathologist Dr. Cheng Ying-Ho said the study raises questions as to whether there is a relationship between the duration of the virus infection in the mother and the severity of fetal brain damage.

Study authors believe that their findings also call into focus the current recommendations for Zika testing in pregnant patients, which suggest testing for presence of Zika within two weeks of the infections and do not recommend MRI scans.

"What really matters is whether there is evidence of changes in the brain to suggest injury in the context of a proven viral infection in the mother," added du Plessis.

The findings are featured in the New England Journal of Medicine.

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