Can a women become pregnant off of pre-cum fluid alone?

The short answer is yes.

The longer answer is that there are a lot of variables.

Do we know that pre-ejaculate fluid can contain active sperm? Yes, we do. We also know that there are far, far less sperm in pre-ejaculate -- when there are any at all -- than there are in a full ejaculation: a full ejaculation contains as many as 100 million soperm, whereas when sperm is in pre-ejaculate, it's more like a few million. But it only takes one active sperm and a few hundred helper sperm to create a pregnancy, so there are more than enough sperm in pre-ejaculate when sperm are present in it to make that happen.

There's no 100% way to know at the time if pre-ejaculate contains sperm, but it's generally agreed upon that it is most likely to when a man has recently ejaculated and has not urinated afterwards (urine flushes the urethra out). It's least likely to contain sperm when a man hasn't ejaculated in a while and/or has recently urinated before he's pre-ejaculating.

We also know that withdrawal isn't a very effective birth control method, and that enough people report using it perfectly -- withdrawing well before ejaculation -- and still becoming pregnant (including my parents as well as a close friend of mine, for a personal perspective), that we'd be remiss to rule out pre-ejaculate as a pregnancy risk. Bear in mind that during the Baby Boom in the United States -- a period in history when we had more births than any other -- that withdrawal was the most common method of birth control people were using.

Too, unprotected sex, period -- ejaculate or no -- poses risks of all sexually transmitted infections, which should be just as great a concern as pregnancy. And pre-ejaculate can transmit the HIV virus just as much as full ejaculate can.

So, having unprotected sex, period, just isn't a good idea unless you are trying to become pregnant AND you and your partner have both been practicing safer sex for at least six months, monogamously, AND each have at least TWO full and clear STI screens under your belts. While it'd be nice if we had more data on pre-ejaculate at this point, at the same time, it's not all that essential. We already have the essential information we need, which is that ANY unprotected intercourse presents risks of pregnancy and STIs.

If you want to engage in intercourse safely, you need a condom at a minimum, and if, for whatever reason, that's not an option than the only good choice is to choose not to have sex until condoms can be used.