Interesting. Probably need a large scale study. My older two have been tested and I recall that DD19 had a 94th percentile PSI, and DD17 had a 96th percentile PSI. DD10 has not been tested, but I would guess a similar PSI. All have brown eyes.

However, based upon the study of my three kids, birth weight should increase the earlier a kid is born. Eldest 3 days early 6lbs 3oz, middle 5 days early 6lbs 13oz, youngest 18 days early 7lbs 10 oz. Hence the need for a large scale study.