The risk of miscarriage drops sharply as pregnancy progresses, and most people are considered out of the highest-risk window by the end of week 12. After that point, the chance of loss falls to around 4% or less. Technically, a pregnancy loss is classified as a miscarriage up until 20 weeks (after which it’s called a stillbirth), but the vast majority of miscarriages happen well before then.
How Risk Changes Week by Week
The earliest weeks of pregnancy carry the highest risk, though many of those losses happen before a person even knows they’re pregnant. A pregnancy that ends around or before 5 weeks is sometimes called a chemical pregnancy because it may only show up as a faint positive test followed by a period that arrives close to on time.
Once a pregnancy is confirmed and progressing, the numbers become more concrete. At 6 weeks, the risk of miscarriage is about 9.4%. By 7 weeks, it drops to 4.2%. At 8 weeks, it’s down to roughly 1.5%, and it continues declining from there. These weekly drops mean the risk changes meaningfully with every passing week during the first trimester.
More than 80% of all miscarriages occur before the end of week 12. Between weeks 6 and 12, about 10 to 15% of known pregnancies end in loss. After 12 weeks, losses make up approximately 4% of pregnancy outcomes. So while there is no single day you cross a finish line, the transition from the first trimester to the second is the most significant turning point.
Why the First Trimester Is the Riskiest
About half of all first-trimester miscarriages are caused by chromosomal abnormalities in the embryo. These are random errors that occur when cells divide in the earliest stages of development. They aren’t caused by anything a parent did or didn’t do. An embryo with a major chromosomal problem typically cannot develop past a certain point, which is why most of these losses cluster in the first several weeks.
This also explains why risk drops so steeply as the weeks go on. If an embryo has the right number of chromosomes and is developing normally, it’s increasingly likely to continue doing so. Each milestone, like a visible heartbeat on an early ultrasound, is a signal that development is on track. By 8 weeks, with a confirmed heartbeat, the statistical odds shift heavily in favor of a healthy pregnancy.
What Happens After Week 12
Reaching the second trimester doesn’t eliminate all risk, but it changes both the likelihood and the nature of potential problems. Losses between 12 and 20 weeks are uncommon, occurring in roughly 1 to 5% of pregnancies, and they tend to have different causes than early miscarriages.
Chromosomal abnormalities account for fewer than 4% of second-trimester losses. Instead, the most common factor is placental problems, particularly infection and inflammation of the placental membranes. One review found that inflammation of the placenta was present in over half of losses between 18 and 24 weeks. Other identified causes include cervical insufficiency (where the cervix opens too early, accounting for about 8% of recurrent second-trimester losses), uterine structural differences, blood clotting disorders like antiphospholipid syndrome, and thyroid conditions. In about half of second-trimester losses, no clear cause is identified.
Because these causes are fundamentally different from the chromosomal issues behind early losses, they sometimes have identifiable warning signs and, in some cases, treatment options. A short or weakening cervix, for example, can be monitored and managed during pregnancy.
The 20-Week Cutoff
In the United States, a pregnancy loss before 20 weeks is classified as a miscarriage. A loss at or after 20 weeks is classified as a stillbirth. This isn’t just a labeling distinction. It reflects the fact that by 20 weeks, the causes, medical response, and experience of a loss are quite different from an early miscarriage. When people talk about being “out of the miscarriage window,” they’re typically referring to getting past the first trimester, but the formal medical definition extends to 20 weeks.
How Age Affects the Timeline
Your overall risk of miscarriage at any given week is influenced by age. For people between 20 and 30, the total miscarriage risk across a pregnancy is about 9 to 17%. At 35, that rises to around 20%. At 40, it’s roughly 40%, and by 45, it reaches about 80%. These numbers reflect the fact that chromosomal errors during egg development become more common with age, which means a higher proportion of pregnancies will have the kind of genetic problems that lead to early loss.
The week-by-week pattern of declining risk still holds at every age. A 38-year-old who reaches 12 weeks with a healthy ultrasound has a much lower risk going forward than she did at 6 weeks. But her baseline risk at each stage is somewhat higher than it would be for someone younger.
After Previous Miscarriages
If you’ve had one or more miscarriages before, you may feel like the “safe” window takes longer to reach. The anxiety is understandable, but the statistics are more reassuring than many people expect. Even after two consecutive miscarriages, there is a 65% chance the next pregnancy will result in a live birth without any medical intervention. More than half of families who experience recurrent loss go on to have healthy pregnancies.
For people with a history of second-trimester loss specifically, the causes tend to be identifiable and sometimes treatable. Conditions like placental inflammation or cervical insufficiency can recur, but knowing about them allows for closer monitoring in a subsequent pregnancy.
Milestones That Lower Your Risk
Rather than thinking of one single moment where you’re “safe,” it helps to understand the milestones that each represent a meaningful drop in risk:
- Confirmed heartbeat (around 6 to 7 weeks): Risk drops significantly once cardiac activity is visible on ultrasound.
- End of week 8: Risk falls to about 1.5% for most people.
- End of week 12: The first-trimester window closes. Over 80% of all miscarriages have already occurred by this point.
- Week 13 to 20: Risk continues to decline, though a small percentage of losses (1 to 5%) happen in this range.
- Week 20: The formal miscarriage window ends. Losses after this point are medically classified differently.
Each of these checkpoints represents real, measurable reassurance. If you’ve passed week 12 with a healthy pregnancy, the odds are strongly in your favor.