I Married A Shadow - 1983 - 6/10
AKA - J’ai épousé une Ombre

Low life boyfriend kicks his pregnant Hélène out of the car and speeds into the horizon.
Dumped, dejected, she boards a train going elsewhere, anywhere.
In the dining car, another female, a pregnant bride, befriends her and allows her to sleep in her cabin while she and new husband have dinner.
After a catastrophe, Hélène is mistaken for the bride by the grieving family.
Part mystery, part character study, as personal ethics conflict with wanting what will be best for the new infant.
The wine growing family, is wealthy, by the way.
I recognized William Irish in the opening credits as a pseudonym for an old mystery writer (Cornell Woolrich).
15 minutes into the film, I recalled the story from a vintage Suspense (OTR) episode, “They Call Me Patrice.”