Miscarriage is most common in the very earliest weeks of pregnancy, with the highest risk occurring before you even know you’re pregnant. The peak risk falls at or before 6 weeks from your last menstrual period (or about 2 weeks after ovulation), when roughly 8% of pregnancies are lost in a single week. From there, the risk drops steadily, falling below 0.5% per week by week 13.
Week-by-Week Risk in the First Trimester
A 2025 study in Fertility and Sterility pooled data from over 12,000 pregnancies and mapped the risk of miscarriage at each gestational week. The pattern is striking: the earlier the week, the higher the risk. At 2 weeks after ovulation (around 4 weeks from your last period), the weekly risk sits at about 8%. In studies that used highly sensitive daily hormone testing to detect pregnancies even earlier, the risk at that stage was closer to 20%.
By weeks 6 and 7 from your last period, the weekly risk drops to about 3%. It continues declining through weeks 8 and 9 (around 2 to 3% per week), then falls to roughly 1% at weeks 11 and 12. By week 13, the chance of losing the pregnancy in any given week is under half a percent.
What this means in practical terms: the first trimester accounts for about 80% of all miscarriages, and the majority of those happen before week 8. If you’ve passed week 10, the odds are strongly in your favor.
Chemical Pregnancies: The Earliest Losses
Many of the earliest miscarriages are chemical pregnancies, which happen before the sixth week of gestation, often just days after a fertilized egg attaches to the uterine lining. These pregnancies produce enough hormone to trigger a positive test but end before anything is visible on ultrasound. Chemical pregnancies account for an estimated 50 to 75% of all miscarriages. Most people who experience one notice only a late, heavy period and may never realize they were pregnant at all.
A clinical miscarriage, by contrast, occurs after the sixth week, when a pregnancy sac or embryo has developed enough to be seen on an ultrasound. The distinction matters because it explains why miscarriage statistics look so different depending on whether very early losses are counted. The commonly cited figure of 10 to 20% of “recognized” pregnancies ending in miscarriage refers mainly to clinical losses. When chemical pregnancies are included, the total loss rate for all conceptions rises to 30 to 40%.
Why the Earliest Weeks Are Most Dangerous
About 50% of first-trimester miscarriages are caused by chromosomal abnormalities. During fertilization, the egg and sperm each contribute a set of chromosomes. If either has too many or too few, the resulting embryo will have an abnormal number. As the embryo’s cells begin dividing and multiplying in those first weeks, errors in this process can also make continued development impossible. These problems are essentially random and not caused by anything the mother did or didn’t do.
The reason risk is concentrated so early is that the first few weeks involve the most critical developmental steps: implantation, the formation of a gestational sac, and the beginning of organ development. An embryo with a serious genetic error will typically fail during one of these early checkpoints rather than progressing further into pregnancy.
The Heartbeat Milestone
Detecting a fetal heartbeat on ultrasound is one of the most reassuring markers in early pregnancy. Research among women with a history of recurrent miscarriage shows that reaching 6 weeks of pregnancy gives a 78% chance of the pregnancy continuing. Seeing a heartbeat at 8 weeks raises that to 98%. By 10 weeks with a confirmed heartbeat, the chance of the pregnancy continuing climbs to 99.4%.
These numbers apply specifically to women who have experienced repeated losses, so they represent a higher-risk group. For women without that history, the odds after a heartbeat is detected are even more favorable.
How Age Affects the Timeline
Maternal age is one of the strongest predictors of miscarriage, and it shifts the overall risk substantially even though the week-by-week pattern (highest early, declining over time) stays the same. Women aged 25 to 29 have the lowest overall miscarriage rate at about 10%. The risk rises rapidly after 30 and reaches 53% among women aged 45 and older. This increase is driven largely by a higher rate of chromosomal abnormalities in eggs as women age.
Second Trimester: A Much Lower Risk
Once you cross into the second trimester at week 13, the risk of pregnancy loss drops dramatically. Only about 1 to 5% of pregnancies are lost between weeks 13 and 19. After week 20, the rate falls to 0.3%. Second-trimester losses have different causes than early miscarriages. They are more often related to structural issues with the uterus or cervix, infections, or blood clotting conditions rather than chromosomal problems.
What Miscarriage Feels Like at Different Stages
The physical experience of miscarriage varies depending on how far along the pregnancy is. Very early losses (before 6 weeks) often feel like a heavy, late period. You might notice slightly more cramping than usual and heavier bleeding, sometimes with small clots. Some people don’t distinguish it from a normal cycle at all.
Miscarriages later in the first trimester tend to be more physically intense. Cramping can be severe, and bleeding is often heavier than a normal period. You may pass large clots and, depending on the week, tissue that’s recognizable as a pregnancy sac. Bleeding can continue for up to three weeks after the miscarriage begins, though it typically tapers from heavy to light spotting over that time.
Early signs that a miscarriage may be starting include vaginal bleeding (which can range from light spotting to heavy flow), cramping or pain in the lower abdomen, and a sudden disappearance of pregnancy symptoms like nausea or breast tenderness. Light spotting and mild cramping are common in normal early pregnancies too, so these signs don’t always mean something is wrong.