In the United States, nearly one in every 33 babies is born with a birth defect, according to the Centers for Disease Control and Prevention.

Ranging from minor to severe, birth defects affect a newborn's organ function, appearance, or mental/physical growth. These defects manifest within the first trimester of pregnancy, a period when the fetal internal organs are still developing.

Extremely severe birth defects are the main cause of infant mortality in the U.S., and are responsible for about 20 percent of deaths in the country.

Since late 2015, an unprecedented link between a mosquito-borne virus and a birth defect known as microcephaly has been causing alarm among pregnant women.

Microcephaly Cases In Brazil

After the threatening health crisis hit the country: an unusual spike in microcephaly cases linked to Zika virus, officials in Brazil urged women to avoid getting pregnant during rainy season when mosquitoes are prevalent.

Microcephaly is a congenital condition in which the size of a newborn's head is abnormally small. The disorder may eventually lead to mental retardation.

About 2,782 cases of microcephaly were recorded in Brazil in November and December, a number tragically higher than that in 2014 which was 147, and 167 in 2013.

Based on the 2015 record, at least 40 babies passed away. Those who survived may face intellectual impairment for the rest of their lives.

How Microcephaly Is Linked To The Zika Virus

Though international scientists say it's too early to be sure, researchers in Brazil have found evidence that the rise in microcephaly cases is due to the Zika virus outbreak that occurred in May. The Zika virus is found in Aedes mosquitoes, the same carrier of chikungunya and dengue fever.

Officials calculate that about 440,000 to 1.3 million individuals in Brazil have caught the Zika virus since May, and because about 300,000 births happen in the country every year, the link between the mosquito-borne virus and microcephaly is strongly worrisome.

"It's a virus we don't know that much about. We are preparing for the unknown," said Fiocruz Research Institute Vice President Rodrigo Stabeli.

Suspicions began when scientists found that 17 microcephaly cases in French Polynesia were recorded after a Zika virus outbreak.

In November, experts in Brazil found the Zika virus genome in amniotic fluid samples from two women whose fetuses were identified to have microcephaly through ultrasound exams. On Nov. 28, researchers also found the Zika virus in the brain tissue of an infant with microcephaly who died.

Dr. Marco Collovati, the founder of OrangeLife, a company in Brazil that is developing a rapid test for Zika virus, said they are uncertain whether it's only the Zika virus that's been killing off infants, or if it's a combination of dengue, chikungunya and Zika.

"Maybe a woman was infected by dengue a year before, and now is pregnant and gets Zika," he said.

With the rise of microcephaly cases, experts have cautioned women in the country to hold off any plans for pregnancy.

Other Causes Of Birth Defects

Birth defects are typically the result of lifestyle behaviors, genetics, exposure to certain chemicals, infections acquired during gestation, or a combination of any of these factors.

Some causes of birth defects are not easy to identify, but harmful behaviors significantly increase the risk for birth defects. Using illegal drugs, smoking and alcohol abuse during pregnancy contribute to the potential development of microcephaly in a fetus.

The CDC also noted that being obese or uncontrolled diabetes during gestation is not good for the fetus, and that the risks of birth defects are high.

Meanwhile, some birth defects are caused by genetic factors. These factors may be linked to environmental factors or problems with chromosomes. Genetic abnormalities occur when a DNA becomes flawed because of a mutation. There are also cases where a part or the entire DNA itself is missing. Experts said these kinds of genetic abnormalities are often unpreventable.

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