That is the concern of some mothers after they noticed that the items - made by Swiss premium brand Medela - discoloured and warped when steam-sterilised.

Mrs Sylvia Goh, 32, is among the concerned parents. She said her Medela SoftFit breast shields turned yellow after a month of use. The breast shields are funnels that work with the breast pumps to collect breast milk.

Mrs Goh, a marketing manager in a multinational firm, said the breast shields have also deformed and "don't fit well".

Unsure about the safety of the warped items, she bought another set from Medela. But they too disfigured after a month.

Another user, Mrs Ho Meiru, 28, a teacher, also encountered the same problem with SoftFit. "I was shocked when I read on a merchant's website that those shields are prone to deform at high temperatures," she said.

J&E Baby and Mothercare Products which mans Medela Singapore's hotline, put the blame on steam sterilisers.

But this explanation has made users even more confused since steaming is a sterilisation method recommended by hospitals.

"I called the hotline and was lold not to use my steam steriliser," said Mrs Goh. She gave birth to her first child, a boy, last month.

A staff member manning the hotline said steam may exceed 100 deg C, which leads to warping and discolouring of the plastic parts.

But this claim was disputed by Dr Leong Lai Peng, a senior lecturer in the National University of Singapore's department of chemistry.

"Steam cannot reach temperatures above 100 deg C in homes in conditions where no salt is added to water,"  she said.

A check of the discussion boards on Medela's United States website revealed that others have voiced similar concerns.

One customer wrote in a posting last July that he received conflicting sterilisation instructions.

A hospital nurse said the bottles must be sterilised every time before use, and the pump parts every 24 hours.

But the reply from Medela, he wrote, was: "You do not have to sterilise after each use ... only once/day Washing the parts of the kit that touch milk and rinsing after each use is good."

Ms Cynthia Pang, assistant director of lactation services at KK Women's and Children's Hospital, said sterilisation - by steam, boiling in water or chemical solution - is "recommended for feeding bottles and accessories for at least the first six months of a baby's life.

She added that commer \cial steam sterilisers "have not been found to be unsafe".

Some parents are playing it safe. Mrs Ling Jiahui, 28, is using sterilisation tablets, which dissolve even in cold water, after her SoftFit breast shields were deformed by boiling water.

When contacted, a Medela spokesman in Switzerland said: "If warping is not excessive, the breast shield will still work well. Yellow discolouring is not unsafe, provided the medium which caused the discolouring is not unsafe."

A spokesman for the Agri Food and Veterinary Authority (AVA) of Singapore said: "Users of the product must follow the manufacturer's instruction. AVA will investigate based on the feedback."