Hong Kong birth study reveals mothers’ migrant status linked to newborns’ weight
25 June 2013
A new study suggests that the migrant status of couples having babies in Hong Kong is a key factor that can be linked to babies’ birth weights. It suggests that couples born in Hong Kong have significantly lighter babies than Mainland Chinese mothers who give birth in Hong Kong. Mainland Chinese couples are only half as likely to give birth to low birth weight children and just one-fifth as likely to give have very low birth weight births as Hong Kong-born couples. ‘Low birth weight’ (LBW) of below 2.5 kg or ‘very low birth weight’ of under 1.5 kg is an important predictor of infant death and illness that can be linked to ill health in childhood and later life, says the study published in the online early edition of Journal of Biosocial Science.
The researchers from Oxford University and the University of Piraeus in Greece examined the data of over 825,000 babies in the Special Administrative Region of Hong Kong between 1995 and 2009.They found that Mainland Chinese couples in Hong Kong were almost twice as likely to have high birth weight babies as Hong Kong born couples. The paper cites other studies showing that high birth weight babies of over 5 kg have a greater likelihood of developing type 1 diabetes in childhood and rheumatoid arthritis, while high birth weight females exhibit higher chances of becoming obese adolescents and developing type 2 diabetes.
Researcher Dr Stuart Basten, from the Department of Social Policy and Intervention at Oxford University, said: ‘Our study appears to support the ‘healthy migrant theory’ of previous studies that suggests recent immigrants have better health than women of the same ethnicity who are not foreign born. We can speculate that in this case, women who have travelled from Mainland China to live in Hong Kong are generally more socially and economically advantaged than the couples who were born in Hong Kong, which is why their babies are heavier.’
Overall, the study found the prevalence of low birth weight births in Hong Kong was low compared to other parts of Asia and Europe. However, migrant women from South and South-east Asia were found to be around 1.3-times more likely to give birth to very low birth weight babies than women born in Hong Kong. Meanwhile, mothers from developed countries were over five times more likely to give birth to heavy weight babies than couples where both partners are born in Hong Kong.
Social and economic factors also play their part as the study found teenagers and single mothers, and especially mothers over the age of 35, face higher risks of poor pregnancy outcomes and particular risks of having babies of low and very low birth weights. Older women are also more likely to give birth to heavy birth weight babies.
Researcher Dr Georgia Verropoulou from the University of Piraeus said: ‘This large-scale study has identified specific high-risk groups that should help policy makers to target groups that need the most support in pregnancy. Single mothers represent a fast growing group worldwide. Meanwhile, immigrants from South and South-East Asia also seem to be an especially susceptible group linked to low birth weight babies. Meanwhile, this study suggests that particular vigilance is also needed for women born in developed countries who should be monitored for heavy birth weight babies.’
For more information, please contact the University of Oxford Press Office on press.office@admin.ox.ac.uk . Alternatively contact Dr Stuart Basten at stuart.basten@spi.ox.ac.uk