Researchers at the Chinese University said many pregnant women in Hong Kong had taken in excessive sodium – doubling the recommendation of the World Health Organisation.

The university surveyed about 160 women in early pregnancy during 2017 to 2018, and found that half of them had taken in too much salt.

Ronald Ma of the university said a high sodium intake could pose serious health risks for pregnant women.

"High sodium intake has been shown to be associated with a higher risk of pregnancy-associated high blood pressure, and also preeclampsia, which is a severe form of high blood pressure during pregnancy," he said.

Ma said problems like preeclampsia could also affect the health of newborns and result in problems like a low birth weight.

Meanwhile, the survey found that pregnant women had not taken in sufficient micronutrients, like calcium and iron, while 97 percent of them did not meet the recommended fibre intake.

Researcher Tsoi Kit-ying said even though most pregnant women did take nutritional supplements, they should not be regarded as a substitute for healthy diet.

"Some of them take in many different types of supplements, but they still eat junk food. That contributes to fat intake or salt intake. We are encouraging mothers to have a more balanced diet instead of relying on supplements," Tsoi said.