THURSDAY, June 16, 2016 (HealthDay News) -- In the first reporting of Zika-related birth defects in the United States, federal health officials said Thursday that three babies have been born with these birth defects while three pregnancies have been lost because of brain damage caused by the virus.
Those six cases will likely not be the last, as 234 pregnant women in the United States have already been diagnosed with Zika infection, according to the U.S. Centers for Disease Control and Prevention. Many of those pregnancies are continuing, and the new statistics don't include any Zika infections in U.S. territories such as Puerto Rico.
While most adults report only mild symptoms with the mosquito-borne disease, infection with the virus during early pregnancy can be far more threatening. Zika has been definitively linked to a devastating birth defect known as microcephaly -- a condition where an infant is born with an abnormally small head and brain.
All of the U.S. cases are linked to travel to areas where Zika has been circulating, and there have not yet been any cases of Zika infection spread within the United States.
But, as the weather continues to warm up and mosquito season arrives, Zika infections and the risk of birth defects are expected to increase in the United States, particularly in Gulf Coast states such as Florida, Louisiana and Texas, health officials have said.
On Wednesday, a new study was released that suggests the risk of Zika-related birth defects may be confined to maternal infections that occur during the first two trimesters of a pregnancy.
Colombian and U.S. researchers studied almost 12,000 pregnancies occurring in 2015 among women in Colombia, a country that is endemic for the mosquito that spreads the Zika virus.
The study detected no cases of infant abnormalities among women who contracted Zika during the last three months of their pregnancy, the researchers said.
They stressed that at the time of the study's publication, 10 percent of the 1,850 women infected late in pregnancy had not yet given birth -- so the data remains incomplete and "preliminary."
Still, data on the other 90 percent of women suggest that "maternal infection with the Zika virus during the third trimester of pregnancy is not linked to structural abnormalities in the fetus," the researchers concluded.
The study was published in the New England Journal of Medicine.
In other Zika news, the CDC on Tuesday announced a plan to respond in a targeted and rapid way to any outbreaks of Zika infection in the United States.
If local infections occur, the affected state can reach out to expert teams from the CDC that will travel to the area. Part of the plan also involves detailed steps on destroying mosquitoes and their breeding sites within 150 yards of the infected person's property, according to the Associated Press.
Such efforts would continue for at least 45 days after the last reported Zika illness in the area, the AP said.
The vast majority of Zika infections so far have occurred in Latin America, and Brazil has been the epicenter with an estimated 5,000 cases of microcephaly. But Zika is now circulating in Puerto Rico, the U.S. Virgin Islands and American Samoa.
Last week, the World Health Organization issued a recommendation that couples who are trying to have children and live in Zika-affected areas should consider delaying pregnancy to avoid having babies born with birth defects.
In the United States, the CDC has refrained from recommending that couples delay pregnancy in Zika-affected areas. However, Puerto Rico's health secretary has issued advice that is similar to the new World Health Organization (WHO) guideline, The New York Times reported.
Mosquito bites remain the most common way Zika is spread, but transmission of the virus through sex is more common than previously thought, WHO officials have said.
Women of child-bearing age who live in an active Zika region should protect themselves from mosquitoes by wearing long-sleeved shirts and long pants, using mosquito repellent when outside, and staying indoors as much as possible, according to the CDC.
President Barack Obama has asked Congress to allocate $1.9 billion to combat the Zika threat, but lawmakers have yet to agree on a spending package.
Visit the U.S. Centers for Disease Control and Prevention for more on the Zika virus.
This Q&A will tell you what you need to know about Zika.
To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.