Most miscarriages happen before the end of the first trimester, with the highest risk concentrated between weeks 4 and 6 of pregnancy. Around 80% of all miscarriages occur within the first 13 weeks, and the majority of those happen before a heartbeat can even be detected on ultrasound. Once you pass certain milestones, the risk drops sharply week by week.
When the Risk Is Highest
The earliest weeks of pregnancy carry the greatest risk because this is when the embryo is first implanting and its cells are dividing rapidly. Weeks 4 through 6 are the peak danger zone. Many of these very early losses are called chemical pregnancies, where a pregnancy test comes back positive but the pregnancy ends before anything is visible on ultrasound. Chemical pregnancies are estimated to account for 13 to 22% of all pregnancies, and many people experience them as a late or heavy period without ever realizing they were pregnant.
Once a pregnancy reaches 6 to 7 weeks and a heartbeat is visible on ultrasound, the risk of miscarriage drops to roughly 10%. That number continues to fall quickly from there. A study of over 300 women found that seeing a heartbeat at 8 weeks meant a 98% chance of the pregnancy continuing, and by 10 weeks that rose to 99.4%. So while weeks 4 through 6 represent the peak risk, every week that passes without problems significantly improves the odds.
Why Early Weeks Are So Vulnerable
Chromosomal abnormalities cause about half of all first-trimester miscarriages. When the egg and sperm merge, each contributes a set of chromosomes. If either one carries too many or too few, the resulting embryo has an abnormal number and typically cannot develop. As cells begin dividing and multiplying in those first few weeks, errors in that process can also stop growth entirely. These are random events, not something caused by anything the pregnant person did or didn’t do.
This is also why miscarriage risk is so tightly linked to age. The chance of chromosomal errors in eggs increases over time. Women aged 25 to 29 have the lowest miscarriage rate, around 10%. That rate climbs steadily after 30 and reaches 53% for women 45 and older. The underlying biology is the same: older eggs are more likely to carry chromosomal irregularities that prevent a pregnancy from progressing past those critical early weeks.
How Risk Changes Week by Week
There’s no single table that perfectly captures every person’s risk, because individual factors like age, health conditions, and pregnancy history all play a role. But the general pattern is consistent across studies. Here’s how it broadly breaks down:
- Weeks 4 to 5: Highest risk period. Many losses happen before a person even knows they’re pregnant.
- Week 6: If a heartbeat is seen, the chance of continuing the pregnancy is about 78%.
- Week 8: With a confirmed heartbeat, the chance of continuing rises to about 98%.
- Week 10: Risk drops to less than 1% with a confirmed heartbeat (99.4% continuation rate).
- Weeks 13 to 20: Second-trimester losses are uncommon, accounting for a small fraction of the overall 80% that happen in the first trimester.
The steep decline between weeks 6 and 10 is one reason many people choose to wait until after an early ultrasound to share pregnancy news. That first scan, typically around 7 to 8 weeks, provides a major reassurance point.
What a Miscarriage Feels Like at Different Stages
A very early miscarriage, around weeks 4 to 5, often resembles a period. You might notice heavier bleeding than usual, some cramping, and a brief delay in your cycle. Some people don’t realize it was a pregnancy loss at all.
Later in the first trimester, the signs become more distinct. Vaginal bleeding can range from light spotting to a flow heavier than a normal period. Cramping and lower abdominal pain are common, and some people notice that pregnancy symptoms like nausea or breast tenderness suddenly disappear. It’s normal to bleed for up to three weeks after a miscarriage.
If a miscarriage progresses on its own, the cramping can be intense, with heavy bleeding and large clots. Medical options to help the process along produce similar symptoms over a shorter, more predictable window.
Missed Miscarriage: When There Are No Symptoms
Not all miscarriages announce themselves with bleeding or pain. A missed miscarriage is when the pregnancy has stopped developing but hasn’t been physically expelled. Many people discover a missed miscarriage only at a routine ultrasound, which can be a shock when they’ve had no warning signs.
Doctors diagnose a missed miscarriage based on ultrasound findings. If an embryo measures 7 millimeters or more and has no heartbeat, or if a gestational sac reaches 25 millimeters with no embryo visible inside it, the pregnancy is considered nonviable. When measurements fall below those thresholds, a follow-up scan is usually scheduled one to two weeks later to confirm, since early pregnancies can simply be too small to evaluate definitively on a single scan.
Recurrent Loss Is More Common Than Many Realize
Recurrent pregnancy loss is now defined as two or more miscarriages, including chemical pregnancies and non-consecutive losses. That definition has broadened in recent years, reflecting growing recognition that even very early losses carry medical significance. Research suggests that each non-visualized pregnancy loss reduces the chance of a subsequent live birth by about 10%, a similar impact to each additional clinical miscarriage.
If you’ve experienced two or more losses, testing can sometimes identify treatable causes like hormonal imbalances, uterine structural issues, or blood clotting disorders. In about half of recurrent miscarriage cases, though, no specific cause is found, and many people go on to have successful pregnancies without any intervention.