This is Star Wars hindering a character because of a natural physical condition isn't fun, it's lame. Pregnant women have their limitations yes, but they are not all consuming handicaps. For the purposes of the game there should rarely be any effects on the mechanics at all, just some additional color to the gms descriptions and that's about it. While Padme may have sat out much of episode three, when the poo hit the fan she didn't hesitate to hop in her chrome ship and fly to volcano planet. No penalties, no weirdness, just play.
However, the fact that the OP even considered a miscarriage based on some die rol tells me that he's probably not mature enough to handle this scenario. Yes, you can work romance and family and other things into a game and have it add quite a lot, but the players and gm really need to know and understand what they are doing and how to handle iit. Probably better to retcon the issue or replace the character in question and move on before you end up getting stereotyped, and maybe revisit the idea down the road when you've got the experience as a gm to answer questions like this before you start. In the mean time if your players insist on hopping in the sack with every cantina waiter/waitress in the galaxy, just assume that the other party (if they are even interested) is on birth control and focus on getting back on the actual adventure.
It was relevant in two novels… nothing immature about the topic except you overreaction to it.
Actually, the part where the original poster asks "does a crit kill the baby" kind of pole-vaulted into the realm of bad taste.
If you *really* have to go here, and I wish you wouldn't, but you want to, so I'm going to say that late 2nd trimester into 3rd trimester I'd either add a flat difficulty die to physical difficulties, or I'd consider upgrading difficulty dice. All non-physicals shouldn't exactly be impacted.
If you're going to expose said woman to combat, either handle it with some "fade to black" level of decorum or find a different hobby.
technicaly i said
"2. Can or should critical hits or multpiple instances of strain to a PC have a chance to cause misscarriage"
i do recall saying Can
The force is not power it is life.