|A city worker sprays chemicals with a fumigator to kill mosquitoes in an effort to control the spread of the Zika virus at a school in Bangkok in September 2016|
Zika causes only mild symptoms in most, including fever, sore eyes and a rash. But pregnant women with the virus risk giving birth to babies with microcephaly -- a deformation that leads to abnormally small brains and heads.
There have been no confirmed cases of Zika-related microcephaly in Thailand so far, but authorities have been monitoring 36 pregnant women infected with the virus.
"If a case of Zika-related microcephaly is confirmed then it would be the first confirmed case in the WHO Southeast Asia region," said Michael Vurens van Es, World Health Organization regional spokesman.
Among the women being monitored by Thai authorities, eight have now given birth and three of the babies have been born with microcephaly, while an ultrasound scan on another mother showed her child also has the condition, according to a ministry statement late Tuesday.
Between 200 to 300 Thai children are born with the condition each year, which can also be caused by Down syndrome and other infections during pregnancy such as German measles and chickenpox, the statement added.
"As of now we cannot conclude that there is a link to Zika," said Suwanchai Wattanayingcharoenchai, a ministry official, in the statement.
"Authorities will have to wait for lab results," he said, adding doctors will meet on Friday to discuss their findings.
Scientists this month warned that the world should prepare for a "global epidemic" of microcephaly as the Zika virus takes root in new countries.
WHO said evidence suggested that Zika has been present in Southeast Asia for several years, adding that the number of confirmed cases has risen in conjunction with heightened surveillance.
Thai authorities have been at pains to reassure locals and the millions of foreign tourists who visit each year that they are fighting the spread of the mosquitos which carry the virus.
Experts say it will be years before a vaccine is developed to prevent infection from Zika.