Professor Cathy Warwick, chief executive of the Royal College of Midwives, said such parties - where people gather to view 3D and 4D scan pictures that have been paid for privately - raise ethical questions.
In a Scrubbing Up column for the BBC News website, Prof Warwick said mothers now give birth later in life and bring with them greater expectations and aspirations about childbirth.
"This ageing of mothers means greater demands on maternity services as pregnancies to older women are more likely to involve complications, which demand more of midwives and others in the maternity team," she said.
"However, I think the worrying trend towards the commercialisation of pregnancy and trend in 'foetus parties' can add to the burden and can increase the expectation for mothers which midwives then have to deal with.
"There is a worry that supposed diagnostic scans are now being used for entertainment. Across the country services for 'foetus parties' are popping up. There are companies across the country that provide gifts for parties featuring images of the foetus, from a fridge magnet for £3 to a teddy with 3D scan image for £15.
"Some companies provide a champagne celebration scan package for £165 and a VIP scan package for £185. This is a far cry from the original purpose of ultrasound."
Prof Warwick said ultrasound is a screening tool to help detect babies with serious problems and ensure pregnancy management is tailored appropriately. He said: "For example, if a baby is found to be growing slowly a decision may be taken to deliver early. However, the trend towards using ultrasound and technology via 'foetus parties' as a 'consumer tool' raises various ethical questions.
"If a woman is celebrating much more overtly than she might normally do regarding a pregnancy at an early stage during the pregnancy and then, at a later stage, a serious problem emerges, a mother may need increased counselling after raising everyone's expectations of her pregnancy at a 'foetus party', only to learn of complications later on."
Prof Warwick also questioned whether it may escalate the thinking among some people that a foetus should have a life of its own before birth and, therefore, rights of its own. He said: "And... what about the foetus? Is this 'yummy mummy' or WAG parenting taken to its absolute zenith and what does it do to the child being 'branded' in this way?"
