Cody Hagel, 18 - who has suffered with the condition for four years - starting mimicking the animals on her family's farm.
Pregnancy often alters the nature of Tourette's - sometimes eradicating it - although scientists are unsure why.
Since she was 14 years old, Cody has experienced between 10 and 20 leg twitches and head jerks a day but her "tics" were never verbal.
But Cody and her family were stunned when she started to make donkey noises - more than 30 times a day - after she conceived five months ago.
She has also started to shout the word "yes" and "haha".
Tourette's is is a neurological disorder characterised by repetitive, stereotyped, involuntary movements and vocalisations called tics.
Motor tics are sudden, brief, repetitive movements that involve a limited number of muscle groups. Vocal tics may include throat-clearing, sniffing/snorting, grunting, or barking. More complex vocal tics include words or phrases.
Pregnancy often alters the nature of Tourette's, possibly because of hormonal changes.
"My Tourette's started with the onset of puberty and I think my pregnancy hormones are probably to blame for the change in my tics," Cody explained.
"The braying started pretty much immediately after I fell pregnant and I've been suffering with it ever since."
The teenager lives with her mum Tanya and dad Dwayne on their farm in North Dakota.
They keep two donkeys called Oliver and Rachel who might be responsible for the teenager's embarrassing affliction.
"It's a familiar sound on the farm so that probably explains why I've started to mimic it," said Cody.
"It is embarrassing but my family are very understanding. If people start looking awkward or staring it makes it worse. So they tend to act like it's completely normal."
Now Cody, a first-time mum-to-be, is worried about passing on the Tourette's to her son, who she has already named Damien, after he is born.
"I've been told that if only one parent has Tourette's the baby has a 50 per cent chance of developing it too," she said.
"I feel bad for him already. But at least if it does happen I'll be able to help him through it."
A spokesperson from Tourette's UK told the Daily Mail: "Research is unclear with regards to the effect of pregnancy on Tourette's - indeed in some women, improvements in tic severity have been reported but not in others.
"The physiological effect of pregnancy may have had some effect on tic severity but it is really hard to know without formally assessing tics before and after pregnancy."
Wow. Did pregnancy have any strange effects on you?
More on Parentdish: Meet the mum-to-be craving road kill!
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