Subsequent births in families of children with disabilities: using demographic data to examine parents’ reproductive patterns.

14 Aug

A team at Vanderbilt University has looked into the question of whether families with disabled children are more or less likely to have more kids. They studied families with children with Down Syndrome and Spina Bifida. The reasons for this was that they could track these directly from the birth records. Disabilities like autism or intellectual disability are not diagnosed until later in life and, thus, would not be in the birth records.

The researchers found that this group of parents were more likely to have one ore more addtional children than parents whose children did not have these disabilities. We can speculate as to the reasons for this. An obvious speculation is the desire to have more siblings who can help nurture the disabled sibling in childhood, and the desire to have additional siblings to help advocate for the disabled sibling after the parents pass.

I would be very interested in whether this tendency for subsequent children would be true for families with an autistic child. There is a very different set of circumstances there. The recurrence risk for autism (or ASD’s) is high, about 20%. Also, there is no prenatal test as there is with Down Syndrome or Spina Bifidia. The counter argument is that given that autism is not diagnosed until later in life (3 years or older is not uncomon), the family might have made the decision to have subsequent children before learning of the child’s disability, or, at least, the specific nature of the disability.

Subsequent births in families of children with disabilities: using demographic data to examine parents’ reproductive patterns.


The authors determined family reproductive patterns after the birth of a child with (vs. without) a disability. Using Tennessee birth records, the authors examined families of children with Down syndrome (N=1,123), spina bifida (N=368), and population group (N=734,189). Families of children with Down syndrome and with spina bifida were more likely to have subsequent children and larger family sizes than the population group. When a 1st-born target child was born, 28.8% of families had a 2nd child in the population group compared with 37.1% and 45.7% when the child had spina bifida or Down syndrome, respectively. Families of children with disabilities were more likely to have subsequent children regardless of maternal race, marital status, and educational level.

One Response to “Subsequent births in families of children with disabilities: using demographic data to examine parents’ reproductive patterns.”

  1. RAJ August 15, 2011 at 11:29 #

    In the fifty years since the discovery of the chromosome mutation (Trisomy 21)responsible for Downs Syndrome a great deal of knowledge about reoccurrance risks for Downs Syndrome has been well established. In Downs Syndrome and Mosaic Downs Syndrome the mutation is not inherited. A tiny percentage of cases are what is called Translocation Downs Syndrome where a parent does not have the mutation but does have an elevated risk for having a Downs Syndrome child . For almost all cases of Downs Syndrome (99%) the risk for a reoccurrance is no greater than population risks for Downs Syndrome. Genetic counselers reassure the parents that they are not at greater risk for a reoccurance than any other family in the general population which may be why parents of Downs Syndrome children are not fearful of having a second child with Downs Syndrome.

    Downs Syndrome with co-occuring autism is far greater than the prevalance of autism in the general population. Ghaziuddin (1997, 2000) compared a group of Downs Syndrome children and their first degree relatives (parents and siblings) with or without co-occurring autism. In Downs Syndrome with co-occurring autism there was an excess of first degree relatives (parents and siblings) who met the description of broad autism phenotype (BAP) features compared to first degree relatives in Downs Syndrome children without autism who did not. None of the first degree relatives with BAP features had Downs Syndrome or autism.

    The twin studies in Downs Syndrome demonstrate that in Downs Syndrome MZ twins are almost always concordant for Downs syndrome while DZ twins are almost always discordant for Downs Syndrome which further obfuscates the concepts of ‘genetics’ and ‘inheritance’ which are all too frequently used by autism researchers as if these concepts were interchangeable.
    The false claim the you can calculate a ‘heritability’ estimate based solely on the difference in concordance rates between MZ and DZ twins would make Downs Syndrome, not autism, the most ‘heritable’ of all the development disorders.

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