Optimal pregnancy spacing in autism spectrum disorders: a multinational study of modifiable risk factors.

First published: August 23, 2021 https://doi.org/10.1002/aur.2599

Commentary

This study will investigate the relationship between the risk of autism spectrum disorder (ASD) and first and second child increased by both short and long interpregnancy intervals (IPI).

A backward-looking cohort study of singleton nonbirths was conducted and analyzed in Denmark, Finland and Sweden from 1998-2007. (N = 925,523 births were included.)

The optimal IPI was defined as the IPI with the lowest observed risk, and a generalized additive model was used to estimate the relative risk (RR) and 95% confidence interval (CI) for ASD.

The population impact factor (PIF) for ASD was estimated under the scenario of changing IPI distribution, ASD (N = 9302), IPI was U-shaped in all countries.

ASD risk was lowest at 35 months for all countries combined (optimal IPI) and at 30, 33, and 39 months for Denmark, Finland, and Sweden, respectively.

The fully adjusted RRs for the 6-, 12-, and 60-month IPIs were 1.41 (95% CI: 1.08, 1.85), 1.26 (95% CI: 1.02, 1.56), and 1.24 (95% CI: 0.98, 1.58).

In the most conservative scenario, the PIF ranged from 5% (95% CI: 1%-8%) in Denmark to 9% (95% CI: 6%-12%) in Sweden, and the minimal ASD risk followed the IPI of 30-39 months in the three countries.

These results may increase the optimal IPI and reduce its indications if they reflect a biological causal effect.