So far the US team has only had success in mice with its antibody treatment, but it says it might eventually lead to a therapy for women who catch Zika in pregnancy.
The Zika virus can severely damage a newborn`s brain.
The antibody therapy is made using blood cells from people who have recently had and fought off Zika.
In mice, the treatment significantly reduced the amount of Zika virus that circulated in the mother`s blood and crossed the placenta into the baby, Nature journal reports.
At birth, there was less damage to the placenta and these baby mice were much bigger than others whose mothers had not received the antibody treatment.
The researchers stress that years of testing will be needed to see if it could be a safe and effective treatment for pregnant women.
In the meantime, other scientists are focusing on making a vaccine that could protect people from catching Zika in the first place.
Zika is spread to people by mosquito bites. Outbreaks of the disease have been seen in the Americas and, more recently, in south-east Asia.
Singapore has said its outbreak was caused by a local strain, not the one which caused the huge outbreak in South America.
Prof Laura Rodrigues, from the London School of Hygiene and Tropical Medicine, said: "At the moment, if a pregnant woman is diagnosed with Zika she only really has one option - whether or not to have a termination.
"Even if we do one day have a vaccine that can protect people from catching Zika, there will still be some who will get infected.
"For these people, a treatment like this antibody one would be helpful."
Zika therapy `works in the womb`
08 November 2016
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Scientists say they may have found a way to protect babies in the womb from the harmful effects of Zika.
