People are infected with malaria from parasites inside mosquitoes
Scientists hope new research may help cut the death toll from two of malaria's most lethal forms.
Placental malaria and cerebral malaria kill hundreds of thousands of young children a year, with the cerebral form deadly in up to 40% of cases.
The Canadian researchers say they have have discovered a distinctive chemical signature for each type.
This gives the option of earlier, or more intense treatment in those who need it, they say.
Billions of people worldwide are under threat from malaria, and the death toll from its various forms is thought to exceed a million a year.
Children can be vulnerable to the disease even before birth, if their mothers - particularly those expecting their first child - develop placental malaria during pregnancy. It causes the birth of underdeveloped or low birthweight babies and the threat of severe anaemia or death to the woman.
However, it was unclear exactly how the malaria parasite could cause these problems.
Specialists from Toronto's McLaughlin-Rotman Centre for Global Health found the women with placental malaria carried a protein called C5a in their blood.
This appears to contribute to an excessive immune response, causing inflammation in the placenta and getting in the way of normal blood vessel growth.
This might well stop the baby getting enough nutrients during pregnancy.
Dr Kevin Kain, who led the research, said: "A test that helps detect placental malaria means women can be treated earlier in pregnancy, reducing the risk of death or or anaemia for them."
Out of balance
Dr Kain was also involved in the second find, a combination of blood vessel-controlling proteins which indicate the presence of cerebral malaria.
In healthy children, angiopoietin-1 and angiopoietin-2 (ANG-1 and 2) are kept in strict balance, but in those with cerebral malaria, the balance disappears.
The bigger the imbalance, the more likely it was that the child would not survive.
The researchers said a test based on the chemicals would help doctors prioritise the sickest children.
Dr Delmiro Fernandez-Reyes, head of the division of parasitology at London's National Institute for Medical Research, welcomed the research, presented at American Society of Tropical Medicine and Hygiene meeting in New Orleans.
However, he said that their findings would need to be validated by other researchers.
He said: "What we are hoping for eventually will be a number of these biomarkers, which, together, will allow doctors to have a clear picture of what is happening in the patient."
An using the biomarker to predict or identify cerebral malaria, he said, would not necessarily be practical, given the sudden onset of the disease.
"A child can be playing happily one day, and the next morning they are in the clinic with cerebral malaria," he said.
He said that the find could offer insights towards new drugs to help fight the disease.
Meanwhile, The Lancet medical journal has reported on a new way to make sure that children with malaria get the treatment they need quickly.
Normally, the only type of malaria medication available away from hospitals and clinics is pills, but children are often so ill that taking them is impossible.
A study looked at the success of a simple suppository version of the drugs, and found that it halved the risk of death or severe disability in patients with severe malaria, who were travelling from rural villages.
Professor Nick White of the Centre for Tropical Medicine, University of Oxford, who helped design the treatment, said: "If you're several hours away from a clinic, it can be the difference between life and death."