Her Sister's Secret (1946)

A WWII tale of romance that begins during New Orlean's "Mardi Gras" celebration when a soldier and a girl meet and fall in love. He asks her to marry him but she decides to wait until his next leave. He is sent overseas and she does not receive his letter and feels abandoned, but she does find out she is pregnant. She gives the child to her married sister and does not see her child again for three years. She returns to her sister's home to reclaim the child, and the soldier, who has been searching for her, also turns up. The sister is not interested in giving up the child. Written by Les Adams

Unfortunately the movie Her Sister's Secret is not yet available on HBO Max.