First-born children showed higher rates of autism, ADHD and food allergies, while second-born siblings faced more substance use disorders and migraines.
https://www.foxnews.com/health/birth-order-linked-150-health-conditions-study-10-million-american-siblings-two-decades
https://www.foxnews.com/health/birth-order-linked-150-health-conditions-study-10-million-american-siblings-two-decades