Discouraging information about infant immunisation during pregnancy causes women to delay immunising babies, but positive information doesn't ensure they will do so on time.
That finding is the latest research from the Growing Up In New Zealand longitudinal study, and is published in the journal Pediatrics.
The ambiguity created by pregnant women receiving conflicting advice about infant immunisation is an area which needs attention, the study's senior author, Professor Cameron Grant, says.
"We cannot prevent pregnant women from being exposed to information discouraging immunisation, but we can improve the ways in which we deliver encouraging information and ensure that they meet the information needs of everyone," he said.
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About a third of 6182 mothers interviewed said they had received only encouraging information, while 9 percent received both encouraging and discouraging advice and 5 percent received only discouraging information.
Of the 44 percent of women who did not recall receiving any information during pregnancy, 70 percent of their infants were immunised on time.
This compares with 57 percent of infants of women who received discouraging information and 61 percent of infants of women who received both encouraging and discouraging information.
The researchers said babies needed to get their shots on time, and the longer babies go without receiving key vaccines, the more likely they are to end up in hospital.
Prof Grant says he was concerned to see one in six women who recalled receiving discouraging information identified health care providers as a source of information.
The main sources of discouraging information were family, friends and media.
"It is clear that pregnant women receiving information which discourages infant immunisation has a negative effect on subsequent health care delivery to that infant, even when they have also received information which encourages immunisation," Prof Grant said.
"In contrast, the receipt of encouraging information about infant immunisation during the pregnancy is no more effective than receiving no information."