Miscarriage is most common before 12 weeks of pregnancy, with the highest risk concentrated between weeks 4 and 6. After week 6, the probability drops sharply each week. By week 8, the risk falls to roughly 1.5%, and it continues to decline from there. Between 10 and 20 percent of known pregnancies end in miscarriage, with the vast majority occurring in this early window.
Risk by Week in the First Trimester
The earliest weeks of pregnancy carry the greatest vulnerability. Many losses happen before a person even realizes they’re pregnant. These very early miscarriages, sometimes called chemical pregnancies, occur within the first five weeks, before anything is visible on ultrasound. A pregnancy test may come back positive, but bleeding starts shortly after, and hormone levels drop back to zero. Because these losses happen so early, they often go uncounted in miscarriage statistics.
Once a pregnancy is confirmed and far enough along to be seen on ultrasound, the numbers become clearer. At 6 weeks, the risk of miscarriage is about 9.4%. By week 7, it drops to 4.2%. At week 8, it falls further to just 1.5%, and it continues to decrease with each passing week. This steep decline is one reason many people choose to wait until around 12 weeks to share pregnancy news.
The pattern makes biological sense. The earliest weeks are when the embryo is implanting, forming its first structures, and beginning cell division at a furious pace. Any major error during this process is likely to stop development entirely. Once the embryo establishes a strong blood supply and begins developing recognizable anatomy, the pregnancy becomes progressively more stable.
Why Early Miscarriages Happen
Chromosomal abnormalities cause about 50% of all first-trimester miscarriages. These are random errors that occur when the egg and sperm combine, resulting in too many or too few chromosomes for the embryo to develop normally. This is not something either parent can prevent or predict in most cases. The embryo simply isn’t viable, and the pregnancy ends on its own.
The remaining first-trimester losses stem from a range of factors: problems with the uterine lining, hormonal imbalances that can’t sustain a pregnancy, or issues with blood flow to the developing embryo. In many cases, no specific cause is ever identified. A single early miscarriage is extremely common and does not indicate a fertility problem or increased risk in future pregnancies.
How Age Affects the Numbers
Maternal age is the single biggest factor influencing miscarriage risk. The overall statistics shift dramatically depending on how old you are when you conceive. Between ages 20 and 30, the chance of miscarriage ranges from about 9% to 17%. At 35, it rises to around 20%, or 1 in 5 pregnancies. At 40, the risk jumps to 40%. By age 45, it reaches roughly 80%.
This increase is driven primarily by egg quality. As eggs age, they become more prone to the chromosomal errors that cause early pregnancy loss. The weekly risk pattern still follows the same curve (highest in weeks 4 through 6, dropping rapidly after), but the overall probability at every point is higher for older parents.
The 12-Week Milestone
Reaching 12 weeks marks a significant turning point. The risk of miscarriage drops dramatically after this point, which is why it’s often treated as a psychological milestone. Once you’ve seen or heard a heartbeat and passed the first trimester, the vast majority of the danger has passed.
Detecting a heartbeat on ultrasound is itself a reassuring sign. The studies showing a 9.4% risk at week 6 and 1.5% at week 8 reflect that once cardiac activity is confirmed, the pregnancy is on a much more stable trajectory. Each additional week with a heartbeat lowers the risk further.
Second-Trimester Loss Is Rare
Pregnancy loss between weeks 13 and 19 occurs in roughly 1% to 5% of pregnancies. The causes at this stage tend to be different from early miscarriage. Rather than chromosomal problems in the embryo, second-trimester losses are more often related to structural issues in the parent’s body. These include cervical insufficiency (where the cervix opens too early without contractions), uterine abnormalities, infections, blood clotting disorders, and problems with the placenta.
Uncontrolled chronic conditions like diabetes and high blood pressure also raise the risk during this period. Smoking and drug use are additional contributing factors. Unlike first-trimester losses, second-trimester miscarriages are more likely to have an identifiable and sometimes treatable cause, which matters for planning future pregnancies.
Missed Miscarriage: When There Are No Symptoms
Not all miscarriages involve obvious cramping and bleeding. In a missed miscarriage, the embryo stops developing but isn’t expelled from the body. You may still feel pregnant, and your body may not show any outward signs of a problem. These are often discovered unexpectedly during a routine ultrasound, typically at the 12-week scan. The scan reveals that the embryo has no heartbeat or stopped growing weeks earlier.
A missed miscarriage can happen at any point in the first trimester, but it’s most commonly diagnosed at that first scheduled ultrasound because that’s when the pregnancy is first visualized in detail. The experience can be particularly jarring because there was no warning. After diagnosis, the options typically include waiting for the body to pass the tissue naturally, taking medication to help the process along, or having a minor procedure to complete it.
What the Numbers Mean for You
If you’re in the early weeks and anxious about miscarriage, the statistics offer a genuinely reassuring trend. Each week that passes without a problem meaningfully lowers your risk. By the time you reach 8 weeks, there’s roughly a 98.5% chance the pregnancy will continue. By 12 weeks, the odds are overwhelmingly in your favor.
If you’ve experienced a miscarriage, the numbers also provide context: this is one of the most common complications in human reproduction. The majority of people who miscarry go on to have successful pregnancies afterward. One early loss, while emotionally painful, is not a sign that something is wrong with your body or your ability to carry a pregnancy.