Moderate iodine deficiency among pregnant women in Hong Kong: revisit the problem after two decades

A survey conducted during 2005 to 2007 by the Centre for Food Safety in Hong Kong suggested that only 5% of the local population had a sufficient dietary intake of iodine. The study, however, was limited as biochemical data (ie urinary iodine concentration) were lacking. Pregnant women are vulnerable to iodine deficiency because of their increased requirement. Recent studies have shown that iodine deficiency in early pregnancy is associated with poorer cognitive development in early childhood. This study reports the iodine status of women during early gestation at an obstetric unit in Hong Kong.

Healthy pregnant women with no history of hyperemesis gravidarum were enrolled into a study when they first made a booking in an antenatal clinic of a public hospital to investigate their iodine status during early pregnancy. All subjects were asked to collect their morning urine for measurement of iodine and creatinine levels. Daily dietary intake of iodine was assessed in a subgroup of participants by structured interview using a standard food frequency questionnaire.

A total of 600 pregnant women were enrolled at a median of 7.0 weeks of gestation. The median urinary iodine concentration and urinary iodine-to-creatinine ratio were 100 μg/L and 98 μg/g, respectively; 429 (71.5%) participants had iodine insufficiency according to the World Health Organization classification. Daily dietary intake of iodine was assessed in 146 participants. The median daily intake of iodine was 69.5 μg and 122 (83.6%) participants had an intake below the 250 μg recommended during pregnancy by the World Health Organization.

Local pregnant women continue to have an inadequate dietary intake of iodine and remain iodine-deficient.