Miles was crossing a street in the city’s Brooklyn Park Slope neighbourhood on 5 March when she and her four-year-old daughter Abigail were knocked down by Dorothy Burns.
Abigail was killed and her mother, whose real name is Ruthie Ann Blumenstein, was taken to hospital.
The 34-year-old was said to be in a stable condition and her unborn child “doing well” in the immediate aftermath, but she and husband Jonathan Blumenstein have now lost the baby girl they had been expecting this month.
Family lawyer Ben Rubinowitz said the miscarriage had come as a direct result of the accident, which has seen Burns charged with manslaughter, criminally negligent homicide, reckless endangerment, assault and reckless driving.
But the 44-year-old cannot be prosecuted for the unborn baby’s death, as state laws regarding homicide do not apply.
“At the time of the crash, Ruthie was pregnant and was severely injured,” said Mr Rubinowitz.
“This past Friday, Ruthie and Jonathan lost their baby, Sophia Rosemary Wong Blumenstein. The pain suffered by Ruthie and Jonathan is nearly impossible to fathom.
“As you might imagine, they are overwhelmed by the sadness of the deaths of their children.”
According to the New York Daily News, among the other people hit by the Volvo S60 was Miles’ friend Lauren Lew and her one-year-old son Joshua, who also died.
A fifth victim, a 46-year-old man, was also hit by Burns.
Other local media reports suggest Burns had been battling various health problems, including multiple sclerosis, and had got behind the wheel against her doctor’s orders.
Six months prior, she reportedly avoided charges after colliding with another woman, leaving her with multiple injuries.
In the wake of the accident in March, a GoFundMe page was set up to raise funds for Miles and her family and raised more than $426,000 (£314,515).
Miles is best known for her Tony Award-winning performance as Lady Thiang in the revival of Rodgers and Hammerstein’s The King and I.
She won for best featured actress in a musical in 2015 and had been due to play the same role in London’s West End this summer.