mother-to-be; expectant mother
Wasei-eigo from English 'pre-mama'. Casual, modern term used especially in pregnancy-related contexts, magazines, and social media. Often paired with プレパパ (father-to-be).
wasei-eigo (Japanese-coined English), from pre-mama
See also: プレパパ
I'm attending a yoga class for expectant mothers.
My friend became a mother-to-be, so I sent her a congratulatory gift.