Does Birth Frequency Affect Chances of Autism?

A new study suggests that having babies at close intervals may increase the risk autism in the second child by up to three times.

Babies who were conceived within a year of their older sibling were found to have the greatest risk. On the other hand, babies conceived within 12 to 23 months and 24 to 35 months of their older sibling also had a heightened risk of being autistic, albeit the risk was not as evident... The study found that second-born children who were conceived within a year of the first-born kids had a more than three times higher to have autism than those who were conceived intervals of more than three years. Moreover, children who were conceived within 12 to 23 months had almost two times the risk of having autism, while those conceived within 24 to 35 months were found to have 26 percent higher odds of having autism, the researchers found.

Wow!  We just conclusively disproved myth that childhood vaccines were causing autism, and now we have a new suspect.  Unfortunately, this one, if it pans out, will directly implicate parents, who have the option of choosing how frequently to have children.  Will autistic children, or their lawyers start suing parents for having them too close to their older sibling?

What mechanisms are offered to account for the increase in autism in the second children from closely space births?

The president of scientific affairs for Autism Speaks, Andy Shih, said that it is not known why closely spaced pregnancies may raise the risk of autism, but that it could be attributed to the mother’s body having insufficient time to recover fully from the impact of the previous pregnancy. Shih said that when you get pregnant so quickly after the first, the environment of the womb may not have undergone a complete recovery to be able to provide optimal support to a second pregnancy. According to the researchers, the first pregnancy may eat up essential nutrients such as folate, and iron, plus the fact that the mother may also have additional stress during the second pregnancy.

But wait, people used to have a lot more kids, one would presume they were closely spaced; why have the rates of autism diagnosis increased recently?

The findings of the study have a special significance because of the trend in women having closely spaced pregnancies. Between 1995 and 2002, the proportion of births taking place within 24 months of a prior delivery went up from 11 percent to 18 percent. The reason for this could be that more women are postponing first pregnancies and are in a hurry to have their second baby due to concerns regarding waning fertility, noted the researchers.

Hmmm, so the decrease in births is actually leading to more closely spaced births, and that, in turn, is increasing autism?  Unintended consequences will get you every time...