Laura Matthews-James, 35, from Pen-y-groes, was seven months pregnant when her Fiat 500 collided with Robert Hitchcock's car on 26 February 2016.
She denies causing death by driving without due care and attention after the crash on the B4300 near Carmarthen.
Swansea Crown Court heard she had no memory of overtaking two vehicles at once before crashing.
Ms Matthews-James, a biomedical scientist, had been on her way to work when she crashed into Mr Hitchcock, 54.
He was killed instantly and she was airlifted to hospital where doctors discovered her baby had died and performed an emergency Caesarean section.
She told Swansea Crown Court she had no memory of the crash but had no reason to rush to her job at Glangwili Hospital in Carmarthen.
She said: "I wouldn't take any risks because I was pregnant.
"My boss was quite flexible as long as I was there around 9am."
She admitted overtaking cars, sometimes two at a time on the same stretch of road on previous occasions, but said there had never been any problems.
She told the court: "You can see quite far ahead."
Asked why she overtook cars if she was not late, she said: "Just because they were going slower than I wanted to go.
"I was going about 40 in a 60 area. I thought to myself, 'I don't want to do 40 all the way to Carmarthen'."
The court heard mud from surrounding fields was found scattered along the road after the crash, which could have created a potential hazard.
Ignatius Hughes QC, defending, said Ms Matthews-James had been diagnosed with post traumatic stress disorder after the combination of the crash and losing her unborn son.
Mr Hughes read out a statement from a forensic psychiatrist who said she had been left in a "fragile and stressed" emotional state.
It said: "She has said she doesn't want to bring a child into the world because in her words 'I've killed my baby'".
The trial continues.
A woman who lost her unborn baby after a head-on crash that killed a man has denied taking a risk by overtaking.