Trimester-stage filter, how do you implement it in Magento attribute architecture?

Three pieces wired together:

• Product attribute: trimester_stage as a multi-select EAV attribute with values first_trimester, second_trimester, third_trimester, postpartum, nursing, plus all_stages for non-stage-specific SKUs (e.g. prenatal vitamins). Stored on every product. Each SKU is tagged with the stages it’s appropriate for.
• Customer attribute: due_date captured at account creation, account settings, or first-order checkout. Magento customer-segment rule auto-bins the customer to first_trimester (weeks 1-13), second_trimester (14-27), third_trimester (28-40), postpartum (40-52), nursing (overlap with postpartum + extended). Recalculates nightly via cron.
• PLP filter UI: Layered Navigation pulls the trimester_stage attribute and exposes it as a filter chip group at the top of category pages, pre-selected to the customer’s current stage if they’re logged in, otherwise expanded as “Which trimester are you in?” as the first interaction.

The killer move: email automation tied to stage transitions. Klaviyo / Listrak fires a different campaign when the customer crosses week 14 (1st → 2nd trimester) vs week 28 (2nd → 3rd) vs week 41 (postpartum). On the merchants I’ve shipped this on, stage-segmented email opens run 38-52% (vs 18-24% on generic) and PDP conversion lift is 18-26%.