Naomi Davies, a 34-year-old nursing assistant from Gloucester, visited Twycross Zoo in Leicestershire.
Accompanied by her fiancé, 40-year-old Ben Billingham, she visited the orangutan enclosure where the “really lovely” moment took place.
A baby orangutan climbed onto its mother’s back, and approached the glass of the enclosure which separates the animals from the viewing public.
While clinging to its mothers back, the baby pressed its face up against the glass to interact with the couple.
Adorable footage, filmed by Mr Billingham, shows Ms Davies pushing her naked pregnant belly against the glass, with the baby orangutan leaning in and repeatedly trying to kiss it.
Mr Billingham, a support worker, said the mum-to-be was incredibly moved by the gesture, and the sweet connection the orangutan had for her baby.
She reported that the mum and her offspring approached the glass and “were watching” the pair before the adorable action took place.
Ms Davies, who described the moment as “really lovely”, said: “We’d been to that zoo once before and absolutely loved it, but this trip was actually the first time I’d seen an orangutan in a zoo.”
She said: “My partner Ben said to try showing her my baby bump as he’d seen interactions from orangutans before.
Orangutans are recognised for the fact that their infants stay with their mother for six to seven years, and form a very close bond during that time.
She described the tender moment and the orangutan’s affection as “quite emotional”.
She said: “Seeing the mother and baby together both being interested in me made me realise the connection between a mother and child”.
The precious interaction between the mother-to-be and the orangutan took place in June 2019, and since then Ms Davies has given birth to a little girl named Constance.
She hopes to take her daughter back to Twycross Zoo in order for Constance to meet the orangutan she shared the special moment with.
Speaking of her intentions she said: “We love the zoo anyway, but I want to see if they come over again and if they recognise Constance!”
Additional reporting by James Bickerton