march to may: the pre-summer baseline window
Spring is also form season. School medicals, summer camp requirements, sports club registrations and pre-travel checks all tend to land between April and June, and a home visit spares you a clinic waiting room with a bored child. Book fasting draws early in the morning while mornings are still pleasant; by June the 7am slots fill with everyone flying out for the summer.
There is a quieter medical argument for spring baselines too: if your annual numbers are always taken in the same season, year-on-year comparisons actually mean something. A vitamin D reading from March and one from October can differ substantially in the same person with no change in health.