Sadly, Miscarriage in the first trimester. Some studies estimate as high as 40% of pregnancies terminate by 12 weeks.
Edit: Since this has gained mild traction I figure I should highlight a through-line featured in a lot of comments: normalize talking about miscarriage.
Obviously folks who have experienced a miscarriage should not be forced to discuss it if they aren't comfortable, but I have seen so many first-time pregnancies that miscarried where their first question was "what did I do wrong?" A significant majority of the time, there is nothing they did that triggered it; the more society is able and willing to provide that reassurance, the better off these people will be.
Edit: Since this has gained mild traction I figure I should highlight a through-line featured in a lot of comments: normalize talking about miscarriage.
Obviously folks who have experienced a miscarriage should not be forced to discuss it if they aren't comfortable, but I have seen so many first-time pregnancies that miscarried where their first question was "what did I do wrong?" A significant majority of the time, there is nothing they did that triggered it; the more society is able and willing to provide that reassurance, the better off these people will be.