Pregnant women are being told to avoid taking fish oil supplements following the results of a study which shocked New Zealand scientists.
"Our recommendation at this time, until there is more information, is not to take fish oil during pregnancy," says lead researcher Professor Wayne Cutfield from the Liggins Institute.
Between 10 and 20 percent of pregnant women are estimated to take fish oil.
Auckland mum-to-be Diane Maxwell is expecting her first child and says she wants to give her baby the best start.
"They have been saying that fish oil helps the brain develop better and that's what I want for my baby."
But this new study has raised concerns about the health effects of taking fish oil during pregnancy.
A separate study last year, also by the Liggins Institute, found most fish oil supplements sold in New Zealand had gone off. So scientists tested it on pregnant rats.
"By the second day of life, almost a third of the baby rats had died," says Prof Cutfield.
"This was an unexpected and fairly dramatic finding.
"In addition we found that the mothers, after they'd stopped taking the fish oil, three weeks after delivery, they were more insulin-resistant which makes them more diabetes-prone."
Prof Cutfield says they expected the study to show some health risks, but nothing so dramatic.
Research fellow Dr Ben Albert emphasises that the results of this study cannot be directly applied to humans.
"Obviously, rats are not humans. Also, it's important to note that the fish oil dose we gave to the rats was higher than doses humans take, but the dose commonly used in fish oil studies in rats."
The Ministry for Primary Industry and the Ministry of Health say the study doesn't prove a risk to humans.
"It is really important that anybody, but particularly pregnant women know, that there is not a food safety issue shown in this study in terms of consumption of fish oil supplements," says Jenny Reid, MPI manager of Food Science and Risk Assessment.
Industry spokesperson and executive director of Natural Products NZ, Alison Quesnel, agrees it's safe.
"There's many studies showing the advantages of fish oil," she says.
"[There is] rigorous testing within their manufacturing and so do the processors of the actual fish oil, so we're confident that our product meets quality expectations."
But she adds any pregnant mother with concerns should always consult their doctor.
So should we be concerned?
"The benefits of fish oil in pregnancy are dubious at best," says Prof Cutfield.
"We don't believe there is serious harm to babies from oxidised fish oil, but there could be some effect - we simply don't know that."
He says more research is needed, but until then he believes pregnant women should avoid it.