The chance of miscarriage decreases significantly after the first trimester, with the sharpest drop happening between weeks 6 and 12. By week 13, the overall risk falls to roughly 1% to 3%, and by week 16 it drops to around 1% or lower. Most people searching for this information are in early pregnancy and anxious about the weeks ahead, so here’s a clear picture of how risk changes over time.
The First Trimester Is When Most Losses Occur
More than 80% of all miscarriages happen before 12 weeks of pregnancy. The overall rate of clinically recognized pregnancy loss is about 15% to 25%, but that number is heavily front-loaded into the earliest weeks. For women under 35, the risk between 6 and 12 weeks is roughly 9% to 12%. Each week that passes without complications chips away at that number.
The single biggest cause of early loss is a chromosomal problem in the embryo. About 50% to 60% of first-trimester miscarriages result from random genetic errors, most commonly an extra or missing chromosome. These aren’t caused by anything either parent did. They’re essentially random events during cell division, and they become more common with age.
Detecting a Heartbeat Changes the Picture
One of the most reassuring milestones is seeing a fetal heartbeat on ultrasound, typically between 6 and 8 weeks. A study published in the journal Obstetrics and Gynecology found that women with a normal heart rate and normal-sized embryo at that scan had only a 5% chance of pregnancy loss. In that same study, 95% of women who had both a normal fetal heart rate and appropriately sized embryo went on to deliver a live baby.
If the embryo measures small for its gestational age or the heart rate is unusually slow, the risk is higher, around 21%. That’s why early ultrasound measurements matter. But for the majority of pregnancies where both markers look healthy, the heartbeat milestone represents a real and meaningful drop in risk.
Week-by-Week Risk After the First Trimester
Once you cross into the second trimester at 13 weeks, the landscape shifts dramatically. Late miscarriage, defined as loss between 12 and 24 weeks, occurs in only 0.7% to 3% of pregnancies. By 16 weeks, the rate drops to about 1%. A large study of more than 264,000 pregnancies found a spontaneous loss rate of just 0.4% between weeks 15 and 21.
The causes of second-trimester loss are also different from earlier miscarriages. Instead of chromosomal problems, late losses are more often linked to issues with the placenta, the cervix, or infection. These are less common overall, which is why the numbers fall so steeply.
How Age Affects the Timeline
Maternal age is the strongest single predictor of miscarriage risk, and it influences how quickly that risk declines. The numbers at each age range look very different:
- Ages 20 to 30: 9% to 17% overall risk
- Age 35: about 20%, or 1 in 5
- Age 40: about 40%, or 4 in 10
- Age 45: about 80%, or 8 in 10
For women over 40, the risk approaches 50% in some estimates. The reason is straightforward: eggs accumulate more chromosomal errors over time. A 40-year-old’s embryos are far more likely to carry genetic abnormalities than a 28-year-old’s, which means the early weeks carry proportionally more danger.
Paternal age plays a smaller but real role. A meta-analysis covering multiple studies found that when the father is 40 to 44, the risk of miscarriage increases by about 23% compared to fathers aged 25 to 29. For fathers 45 and older, the risk rises by roughly 43%. For first-trimester losses specifically, the increase for fathers over 45 was even steeper, at about 74%.
Chemical Pregnancies: Losses Before You Even Know
Some losses happen so early that they never show up in the standard miscarriage statistics. A chemical pregnancy is a very early miscarriage that occurs within the first five weeks, before anything can be seen on ultrasound. The only sign of the pregnancy is a positive test driven by rising hormone levels, which then drop quickly. Many chemical pregnancies happen before a missed period or are mistaken for a late, heavy period.
Because chemical pregnancies often go unrecognized, they aren’t counted in the 15% to 25% figure for clinically recognized losses. If they were included, the true rate of all conceptions that fail to progress would be considerably higher. This is worth knowing because it means if you’ve experienced one, it’s extremely common and doesn’t indicate a fertility problem.
Risk After a Previous Miscarriage
If you’ve had one miscarriage, the risk of it happening again is about 20%. That’s only slightly higher than the baseline rate for any pregnancy. The vast majority of people who experience a single loss go on to have a healthy pregnancy afterward.
Recurrent pregnancy loss, typically defined as two or more consecutive miscarriages, is less common and more likely to have an identifiable underlying cause such as a hormonal imbalance, uterine structural issue, or a blood-clotting disorder. After three or more losses, evaluation for these causes is standard.
IVF Pregnancies Follow a Similar Pattern
If you conceived through IVF, your miscarriage timeline is broadly the same as for natural conception. Research comparing chromosomal findings in miscarriages from IVF and natural pregnancies found that IVF does not increase the risk of loss due to abnormal embryonic genetics. In women under 35, IVF miscarriages actually showed a lower rate of chromosomal abnormalities (37%) compared to natural conception miscarriages (62%), likely because embryo screening catches some problems before transfer. In women 35 and older, the rates were more similar between the two groups.
The age-related increase in miscarriage risk still applies to IVF pregnancies, particularly when using the patient’s own eggs rather than donor eggs. The reassuring milestones, like detecting a heartbeat and reaching the second trimester, carry the same significance regardless of how conception happened.