How to read the band →
Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Martha
Martha is now well below its former popularity. All-time it's been given to 553,732 U.S. babies, the 1,162nd most common name by sound today, peaking at 10,673 in 1947, with 393 in 2025.
Martha has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).