Smoke engulfed their cities. Did it make their children sick?

Six years after Black Summer, parents and doctors face an unsettling question: What does bushfire smoke do to babies in the womb? (Grist: Amelia K. Bates)

Six years after Black Summer bushfires, parents and doctors face an unsettling question: What does bushfire smoke do to babies in the womb?

This story is a collaboration between the ABC's climate team and climate media organisation Grist.

They never thought the fires would reach them. They lived in cities, after all, far from the parched, combustible bush.

There's the woman who never expected to have to grab her one-year-old out of bed in the middle of the night, shielding her soft head from a hailstorm of flaming embers as she dashed to the car.

Or the mum of two who wound up on the beach holding her youngest, a nine-week-old baby, wondering how she would swim if the fires bearing down on her from the hills above forced her into the ocean.

Or the pregnant asthmatic who had to decide where to put her air purifier as suffocating smoke blanketed her neighbourhood — in her own bedroom, or the bedroom of her eldest child.

These women don't know each other, but they share the same instinctive feeling that they didn't know enough — and didn't do enough — to keep their children safe.

As urban sprawl encroaches on the bush, and as the planet grows drier in many places and hotter almost everywhere, bushfires are becoming more dynamic, unpredictable and far-reaching, affecting broader swaths of the world's population.

On the east coast of Australia and the west coast of the United States, two of the planet's most densely populated wildfire hotspots, millions now find themselves in the midst of a public health crisis that is not yet fully understood.

Even fires that are limited to wilderness can blanket major cities in levels of pollution that are without recent precedent, leaving residents to guess how to protect themselves and their families. And when bushfires push through city limits, they incinerate synthetic materials, vehicles and buildings, producing a mix of pollutants more toxic than the smoke that comes from burning vegetation.

This story is part of a Grist series called Vital Signs, exploring how climate change impacts human health. The reporting initiative is made possible thanks to funding from the Wellcome Trust.

None of this is theoretical. It's been six years since Australia's Black Summer bushfires coated the country's east coast in choking smoke, three years since 100 million Americans were exposed to deadly pollution from Canadian wildfires, and just one year since fires decimated