Women who take multivitamins while pregnant lower their risk of having an underweight baby.
So concludes a major new study by Canadian researchers that challenges the World Health Organization strategy of recommending iron and folic acid supplements alone.
Low birth weight is a leading cause of illness and death in newborns, and a condition that has lasting effects throughout life. Newborns weighing less than 2,500 grams — about 5 1/2 lbs. — are considered to be underweight.
In 2008, a total of 367,089 babies were born in Canada. About six per cent were low birth-weight babies. That's up from 5.7 per cent of hospital births in 2001-02. No one knows why the rate is increasing, but one theory attributes it to a greater frequency of multiple births, such as twins and triplets, from reproductive technologies. The rate also goes up significantly for women 35 and older.
Babies born weighing less than normal are at a higher risk of being admitted to the intensive care unit. They also have an increased risk of infections, feeding problems, cerebral palsy, poor growth and mortality.
And the risks continue as the child grows: Several studies have linked low birth weight to problems with thinking, learning and memory in childhood, as well as to a higher risk of heart disease, diabetes, depression and other chronic illnesses in adulthood.
The World Health Organization currently recommends, based on a review it did in 2005, that all pregnant women take iron and folic acid supplements to improve fetal growth and to prevent spina bifida and neural tube defects.
When WHO compared studies available at that time, it concluded multivitamins didn't add any extra benefit over folic acid and iron alone, the Canadian researchers say. But since then, several randomized, controlled trials have been done.
The Toronto team pooled the results of 13 studies, including more recent ones, and found that, compared to placebos, or sugar pills, "multivitamins were effective in reducing low birth weight," says lead author Dr. Prakesh Shah, a neonatologist at Mount Sinai and associate professor at the University of Toronto. Compared with iron and folic acid alone, multivitamins lowered the risk of low birth weight by 17 per cent.
Multivitamins are thought to boost immune function in women, improve their overall nutritional status and improve fetal growth.
Overall, the birth weight of babies was 54 grams higher, on average, among babies born to women given multivitamins than among those who received iron-folic acid supplements alone.
The Society of Obstetricians and Gynaecologists of Canada recommends pregnant women take folic acid in combination with a multivitamin supplement, but primarily for the prevention of neural tube defects and other congenital anomalies.
Shah says different studies used different vitamin combinations, but the components that came out consistently in his team's review included:
Vitamin A (2,640 IU, or international units), vitamin D (200 IU), vitamin E (10 milligrams), vitamin B1 (1.4 milligrams), folic acid (400 micrograms), vitamin C (70 milligrams), zinc (15 milligrams) and iron (30 milligrams). Shah says women should start taking multivitamins as soon as they know they are pregnant and continue taking them throughout their pregnancy.
But Dr. Vyta Senikas says women should start taking supplements as soon as they are thinking of conceiving.
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