Multi-region maternity sizing, US vs EU vs UK, how do you handle it in Magento?

Maternity sizing is messier than fashion because each region uses different number conventions and the pre-pregnancy-to-current mapping varies by brand.

• US: XS / S / M / L / XL / 1X / 2X / 3X for apparel; band 30-46 + cup B, K for nursing bras.
• UK: 6 / 8 / 10 / 12 / 14 / 16 / 18 / 20 (typically US + 4); band 30-46 + cup B, K (mostly matches US, with some divergence at K+).
• EU: 34 / 36 / 38 / 40 / 42 / 44 / 46 (typically US + 30); band 65-105 (different numbering entirely; conversion table mandatory) + cup B, K.
• AU: mostly matches UK (8 / 10 / 12 ...) with some maternity-specific deviations.

Magento implementation:

• Multi-Source Inventory (MSI) with sources per region. Same SKU pool, different stock per source.
• Store views per region, en_US, en_GB, en_AU, de_DE, fr_FR. Each store view shows the right size labels via Magento’s attribute options per store-view configuration.
• Single underlying attribute with per-store-view labels, the size attribute value is the SKU-level canonical size (often stored as US numeric); the displayed label changes per store view. One SKU, multiple labels.
• Size-converter widget on PDP, shows the customer their size in their region + cross-region equivalents. Magento custom block, Hyvä-rendered.
• Pre-pregnancy size capture at account creation, lets the recommendation engine compute “your maternity size in this brand” reliably.

The thing that breaks most maternity stores at multi-region: belly band sizing uses circumference (in inches or cm) rather than dress size, it doesn’t map to S/M/L. Build a separate belly_band_size attribute with cm-based values (e.g. 65cm, 75cm, 85cm) and a region-aware unit toggle on the PDP fit guide.