Each year, the Centers for Disease Control and Prevention (CDC) conduct a National Immunization Survey (NIS) in all 50 states, the District of Columbia, and selected geographic areas within the states. Random-digit dialing is used to survey households with age-eligible children.

Approximately 35,600 telephone interviews are obtained nationwide. Respondents are described as the person who is most knowledgeable about the child’s immunization status. Children are 19 to 35 months of age at the time of the interview.

Since July 2001, breastfeeding questions have been part of the NIS. The breastfeeding questions were modified in 2004 and 2006 based on cognitive testing of the questions. In the past, breastfeeding data were presented based on the year in which the data collection occurred. For example, the 2005 NIS was conducted in 2005 but the percentage of children reportedly breastfed at birth, six months, and 12 months, represented children born between February 2002 and May 2004.

In an effort to more accurately track and report national breastfeeding trends, NIS breastfeeding data is now presented by year of child’s birth. Among U.S. children born in 2004 - 73.8 percent were ever breastfed, 41.5 percent were breastfeeding at 6 months, and 20.9 percent were breastfeeding at 12 months. In addition, 30.5 percent were breastfeeding exclusively at 3 months and 11.3 percent were breastfeeding exclusively at 6 months.

Comparative data from the Ross Mothers Survey (RMS) show that among children born in 2004 - 64.7 percent were breastfeeding at birth, 31.9 percent were breastfeeding at 6 months, and 19.8 percent were breastfeeding at 12 months. Additionally, 41.7 percent were breastfeeding exclusively at 3 months and 17.4 percent were breastfeeding exclusively at 6 months.

A decline in breastfeeding rates from 2005 to 2006 was the subject of a previous post on baby gooroo®. Because the most recent NIS data targets children born in 2004, no comparison can be made with the 2006 RMS data.

How do the surveys differ?

The RMS has been used by Ross Products Division of Abbott Laboratories since 1955 to collect information on breastfeeding among U.S. children. The RMS is a mail survey as opposed to a telephone survey. It is sent periodically to a representative sample of mothers when their infants are one month of age, two months of age, three months of age, and so on until 12 months of age. Mothers are asked to recall the type of milk fed to their infant in the hospital and during each month of age. Only two categories of breastfeeding are considered - any breastfeeding (human milk or a combination of human milk and formula or cow’s milk) and exclusive breastfeeding (only human milk).

In 2001, 1.4 million questionnaires were mailed with a response rate of 31 percent or 43,400. Questionnaires are sent to a geographically representative sample of mothers, however each recipient decides whether or not to respond creating an element of self-selection. NIS respondents are randomly selected.

One advantage of the RMS is that it is conducted when children are 12 months of age or younger, while the NIS is conducted when children are 19 to 35 months of age. Theoretically the older the child the greater the risk for recall bias. Like the NIS data, the RMS data reflects the child’s birth year. However there is a delay of 2-3 years between when a child is born and when the NIS data is made public. Currently RMS data is available 1 year after the child is born.

For more information about the 2006 RMS data please contact Ross Products Division of Abbott Laboratories. If you are unable to access the 2006 data please contact Amy Spangler.

For more information about breastfeeding rates among children born in 2004, including rates by socio-demographic factors, please visit the CDC website.