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A rare birth defect is on the rise in Washington State, and the bizarre trend has health officials stumped.

The odd development was brought to light in 2012 by Sara Barron, who was working a nurse at Prosser Medical Hospital in rural Washington at the time.

That year, Barron encountered two cases of babies born with anencephaly - a neural tube birth defect that causes infants to be born without certain areas of the brain and skull. A devastating condition that affects only one or two babies out of every 10,000 pregnancies, anencephaly occurs when the upper part of the neural tube doesn’t close all the way during the first month of pregnancy.  Almost all babies born with this condition die shortly after pregnancy.

“We had this first case, and it’s horrifying,” Barron, now a nursing instructor at Washington State University, told FoxNews.com.  “And then less than a month later, we had another mother come in and have a baby with anencephaly… and it affected the whole hospital.  But I thought, two in two months with a hospital that small – that’s a lot.”

Throughout her entire 30-year nursing career, Barron had only encountered this birth defect twice before. Then, when Barron heard of another case of anencephaly at a hospital 30 miles away, she decided it was time to inform the Washington State Department of Health (DOH).

“As a member of the infection control group [at Prosser], we all meet once a month at the health department with lead epidemiologists in our area,” Barron said.  “And I said, ‘This isn’t infectious per se, but I’ve become aware of three cases [of anencephaly] in two months.  Has anyone else seen anything like this?’  And another person from another tiny hospital said, ‘Yeah, we just saw one.’  It was way too many in this small of an area.”

Barron’s report eventually sparked a state DOH investigation. After looking over hospital and medical records spanning a three-county area in the state, health officials found that the birth defect was indeed increasing in the region.

According to the report, published by the Centers for Disease Control and Prevention (CDC), there were a total of 23 anencephaly cases in the Washington state region between January 2010 and January 2013, equating to 8.4 cases per 10,000 live births. Comparatively, throughout the country there were an average of only 2.1 anencephaly cases per 10,000 live births during the same period.

So far, state health officials do not know what is behind this localized trend.  A state-led study looking into potential causes of this increase found “no common exposures, conditions, or causes.”  The state’s department of health noted the difficulty of using medical records to figure out the problem.

“Medical record reviews might not have captured all information, preventing a cause from being identified,” the Washington State Department of Health said in a press release.

While the exact cause of the Washington cases hasn’t been determined, Barron said she believes the pregnancies might have something to do with the agricultural industry – since most of the mothers affected have been from rural communities.

“If I was going to have a theory, I would say there’s something agricultural, like [new] pesticides or insecticides, which are known to cause neural defects,” Barron said.  “It’s a random guess, but all these women are so extremely rural.  Maybe it’s mosquito sprays, because the likelihood is high of them being in the fields or exposed to husbands in the field.  Plus these were all upstream and way upwind, so it’s not radiation from Handford – a big nuclear facility in the area.”

Health experts believe that many factors including genes, behaviors and the environment may contribute to incidences of anencephaly.  According to the CDC, a low intake of folic acid in the first month of pregnancy can increase a woman’s risk of having a baby with neural tube defects – including anencephaly.

With so much mystery surrounding these anencephaly cases, Barron believes that more could ultimately be done to get to the root of the problem.  She argued that health officials could utilize student researchers to conduct the investigation or interview mothers in the area.

“I wish they could have done more…I know the state looked at drinking water and well water, and they said there was no difference between healthy deliveries and abnormal deliveries,” Barron said. “But because we didn’t do any interviews with the women, we don’t know for sure what water these women were drinking when they conceived. Even in medical records, we don’t necessarily know how early they started taking folic acid.  We don’t know for sure what they were taking and when."