Chances of miscarriage by week

How it works

How it works as a count is a week number plus a group, not a private lottery ticket. Clinicians call early pregnancy loss a miscarriage before 13 completed weeks. About 10 in 100 known pregnancies end that way. Many other losses happen so early that a test was never taken, so they never enter that “known” 10.

Most pregnancy losses that will happen, happen in the first trimester. The chance is not a flat line across forty weeks. It is higher at the start, when a pregnancy may never develop a heartbeat, and lower later, once a pregnancy is well established. Seeing cardiac activity on an ultrasound is one mark of a pregnancy that is progressing. Absence of that activity on a very early scan can also mean it is simply too soon. Repeat dates belong to a clinic, not to a guide.

Weeks themselves are a ruler. Ordinary clinical dating counts from the first day of the last menstrual period, or from a date a clinician assigned. A “week 6” and a “week 12” are 42 and 84 days on that ruler if the start is known. Mixing a home-app week with a clinic week is how people invent a risk that applies to neither clock.

Early loss: before 13 completed weeks, in common U.S. clinical language. About 10 in 100 known pregnancies end in that early loss. The chance is higher in the earliest weeks and lower later. Age and a prior loss are among the factors clinicians weigh; a webpage is not one of those factors.

About half of early miscarriages involve a pregnancy that did not develop as expected, often a chromosome problem. That is a statement about biology, not a verdict that someone caused week 7 by lifting a bag. Week numbers do not punish. They label time.

Why a week-by-week table is the wrong object

People ask for a percentage beside week 5, week 8, week 12, as if each square of the calendar had an official odds printed on it. Groups differ by age, by whether the pregnancy is already visible on ultrasound, by whether cardiac activity has been seen, and by whether the person even knows they are pregnant yet. A single column of percentages cannot hold those groups. Sticking one number on “week 6” for everyone is a false calm or a false panic, both of which are still false.

What you can honestly say without a chart: as completed weeks accrue, the remaining chance of miscarriage in a progressing pregnancy tends to fall. After the first trimester, loss is less common than in those first weeks, and a later loss is named and handled differently. After 20 weeks, clinicians use other terms than miscarriage. The vocabulary change is not a superstition. It is a different part of the timeline.

If you are bleeding, cramping, or frightened, a percentage from the internet is not care. Contact a clinician. If you have had more than one loss, that is also a clinical conversation. Repeated miscarriage is uncommon relative to a single early loss. Most people who have one early loss later have a pregnancy that continues. That sentence is hope with a boundary: it is a pattern in a population, not a coupon for your next week.

A week number is a count from a start date. It is not a verdict on a person, and it is not a private odds table with your name at the top.

Counting the week you actually mean

Write the start beside the week. “12 weeks from last period” can be checked. “12 weeks because an app guessed from a symptom” cannot. If two apps disagree, they are using different starts or different midnights. Pick the dating your clinic uses and stay on it when you talk about chance, because chance talk without a start is theatre.

The first trimester in common U.S. grouping runs through 13 weeks 6 days. Week 4, week 8, and week 12 are marks on that same seven-day stick, not three different diseases. What changes is how much of the early-risk window you have already walked through, and what a scan can already show.

Do not convert a week number into a promise, a neighbour’s story into your percentage, or two internet tables into an average. A number that belongs to you has to come from the person who has your age, your history, and your ultrasound.