It as not as though there was no contraception back then. My grandmother, a woman who was actually older than Ingrid, swore by her diaphragm. She said the only time she didn't use it, was when she got pregnant.
There is naturally always the possibility but when it comes to a certain passion like patriotism in this sense, there are worse such ramifications. Death, for instance. She was almost murdered so getting pregnant was probably one of the least of her worries.
I don't know how well your stomach is for violence and sex, but there is a show on now that demonstrates this very aspect. It's a really great show, but there is definitely a lot of explicit sex and violence. It's on a regular cable channel, not a paid channel, so it's not like Game of Thrones. Still, it's much more explicit than any other show on TV that I know of.
Anyway, it's an amazing show. It is considered by many (Variety Magazine, et al) as the very best show on television right now. It's called The Americans (2013). Past seasons are available on Amazon Prime, if you have that. Granted, it's not the 40s where there was not a near 99.9% effective piece of contraception, but it demonstrates the ideology behind your love of country and how far you area willing to go.
Hopefully I don't sound sarcastic or rude. I'm often told that I come off that way. I'm just trying to explain the psychology of it and make a suggestion that demonstrates it quite well.