"Children born after an IPI [interpregnancy interval] of <12 months or ≥72 months had a 2- to 3-fold increased ASD [autism spectrum disorder] risk compared with children born after an interval of 36 to 47 months."
So said the study results published by Ousseny Zerbo and colleagues  looking at the increasingly interesting area of the autism research landscape: the interpregnancy interval (the time from the birth of an index child to the next conception/pregnancy of a sibling).
Looking at data derived from children "born at Kaiser Permanente Northern California (KPNC) between 2000 and 2009", researchers examined the IPI to evaluate the risk of ASD in second-born children. Various hazard ratios (HRs) are reported based on the spacing between children: "<6 months, 3.0 (1.9–4.7); 6 to 8 months, 2.1 (1.4–3.3); 9 to 11 months, 1.9 (1.3–2.1); 12 to 23 months, 1.5 (1.1–2.1); and ≥72 months, 2.4 (1.5–3.7)." Following a sort of U-shaped response curve and taking into account various factors that may potentially impact on offspring autism risk, researchers concluded that: "Children born after interpregnancy intervals <2 years or >6 years may be at increased risk of ASD."
Whilst the Zerbo findings have attracted some media attention (see here and see here) it is not necessarily new news that the IPI might show some connection to offspring autism risk. I've covered the topic on at least two other occasions on this blog (see here and see here) outside of other research suggesting similar things . The findings are fairly robust and importantly, seem to cross different geographies and different ethnicities, suggesting that the IPI might be something generalisable to autism across the globe.
As per my other musings on this topic, there are several possibilities as to how a short (or long) IPI might impact on offspring autism risk, mainly associated with more general research on how IPI might influence various birth outcomes (albeit with caveats ). Having watched the recent BBC series called 'Countdown to Life' documenting the nine months that made us, I'm particularly interested in the idea that there may be more than one mechanism at work depending on the IPI. Specifically, whether a short IPI where the greatest HR was reported by Zerbo, might be related to a depletion of maternal stores of various micronutrients (the authors have talked about folate although I'd be careful there, indeed very careful there ) that comes with pregnancy and David Barker style (see here) whether intrauterine health might be a factor in the elevated risk?
Music, and something a little 'cool' today: The Specials And Fun Boy Three - Our Lips Are Sealed (complete with a sample of the Go-Go's).
 Zerbo O. et al. Interpregnancy Interval and Risk of Autism Spectrum Disorders. Pediatrics. 2015. Sept 14.
 Coo H. et al. The association between the interpregnancy interval and autism spectrum disorder in a Canadian cohort. Can J Public Health. 2015 Feb 3;106(2):e36-42.
 Ball SJ. et al. Re-evaluation of link between interpregnancy interval and adverse birth outcomes: retrospective cohort study matching two intervals per mother. BMJ. 2014; 349: g4333.
 Virk J. et al. Preconceptional and prenatal supplementary folic acid and multivitamin intake and autism spectrum disorders. Autism. 2015 Sep 25. pii: 1362361315604076.
Zerbo, O., Yoshida, C., Gunderson, E., Dorward, K., & Croen, L. (2015). Interpregnancy Interval and Risk of Autism Spectrum Disorders PEDIATRICS DOI: 10.1542/peds.2015-1099