The risk of miscarriage is highest during the earliest weeks of pregnancy and gradually decreases as the pregnancy develops. Most miscarriages happen during the first 12 weeks of pregnancy a period sometimes called the first trimester. The risk drops significantly once a heartbeat is seen on an ultrasound and continues to decrease throughout the second trimester. While no pregnancy comes with zero risk, most pregnancies continue normally beyond the first trimester.
A miscarriage is the loss of a pregnancy before 20 weeks of gestation; a loss occurring at or after 20 weeks is classified as a stillbirth. Miscarriage is much more common than many people realise studies estimate that up to one in five recognised pregnancies end in miscarriage, with most occurring in the first 12 weeks. The true number is likely higher, as some very early losses are mistaken for a normal period.
Miscarriage Risk by Week: Quick Reference Table
The table below combines general population estimates with findings from a large 2025 pooled-cohort analysis published in Fertility and Sterility, which tracked 12,390 pregnancies (2,635 miscarriages) across six major U.S. pregnancy-planning cohort studies not using assisted reproductive technology (ART).
| Gestational Stage | Estimated Miscarriage Risk | Source / Basis |
| Weeks 1–4 (from LMP) | 10%–25% | General population estimates; early losses often present as a late/heavy period (chemical pregnancy) |
| ≤6 weeks (from LMP) | ~4% | 2025 pooled-cohort study, Fertility and Sterility (12,390 pregnancies) |
| Weeks 5–8 | 5%–10% | General estimates; 2008 Australian cohort study: 9.4% at 6 weeks, 4.2% at 7 weeks |
| Weeks 9–12 | 3%–5% | 2008 Australian cohort study: ~1.5% at 8 weeks post-heartbeat detection |
| Weeks 13–16 | 1%–3% | General population estimates |
| Weeks 13–19 | <0.5% | 2025 pooled-cohort study, Fertility and Sterility |
| Weeks 17–20 | <1% | General population estimates |
What the Risk Looks Like Week by Week
Weeks 1 to 4
During the first few weeks of pregnancy, miscarriage risk is at its highest, with general estimates placing it between 10% and 25%. Many losses this early are chemical pregnancies occurring shortly after implantation, before five weeks and many people don’t realise they were pregnant. What seems like a slightly heavier or later-than-usual period may actually have been a very early pregnancy loss. These early losses are usually caused by factors completely outside anyone’s control.
Weeks 5 to 8
By weeks five to eight, risk begins to decrease as the pregnancy develops, with general estimates around 5% to 10%. A 2008 Australian cohort study found the chance of miscarriage was approximately 9.4% at six weeks, dropping to 4.2% by seven weeks. This aligns with the 2025 Fertility and Sterility pooled-cohort analysis, which found risk highest at six weeks or earlier from the last menstrual period (around 4%), declining steadily from there.
Around this time, many people have their first ultrasound and hear the baby’s heartbeat a major milestone. While it doesn’t remove the risk completely, it is a strong positive sign the pregnancy is progressing well. If a heartbeat isn’t seen at the first scan, try not to panic; it is sometimes simply too early, and your healthcare provider may recommend a follow-up scan a week later.
Weeks 9 to 12
Risk continues to fall through the remainder of the first trimester, with general estimates around 3% to 5%. In the 2008 Australian study, risk at eight weeks (once a healthy heartbeat had been detected) was around 1.5%, continuing to decrease as the pregnancy progressed.
Weeks 13 to 20
Once the second trimester begins, miscarriage risk becomes much lower around 1% to 3% between weeks 13 and 16, and under 1% between weeks 17 and 20. This is strongly supported by the 2025 pooled-cohort study, which found risk between weeks 13 and 19 had fallen below 0.5%. Pregnancy loss after 20 weeks is no longer classified as a miscarriage it is known as a stillbirth.
New diagnostic tools are also making it possible to assess miscarriage risk earlier in pregnancy. Read more in our guide to a new blood test for miscarriage risk.
What causes most miscarriages?
One of the hardest parts of miscarriage is wondering why it happened. In many cases, there isn’t anything the parents could have done differently. Research shows that around half of all miscarriages happen because of chromosomal abnormalities in the embryo genetic changes that occur by chance during conception and prevent normal development.
Other factors that can increase the likelihood of miscarriage include:
- Increasing maternal age
- Sperm-related factors, such as sperm DNA damage, chromosomal abnormalities, and lifestyle factors like obesity that affect sperm quality
- Certain medical conditions, such as uncontrolled diabetes or thyroid disorders
- Uterine conditions, including some fibroids
- Smoking, alcohol use and high caffeine intake
- Very low or very high body weight
- Previous miscarriages
- Some hormonal disorders and blood clotting conditions
Read: Recurrent Miscarriages? The Cause May Lie in Sperm Quality
It’s also worth remembering that miscarriage is common. Studies estimate around 15% of recognised pregnancies end in miscarriage, while experiencing three or more miscarriages in a row recurrent pregnancy loss (RPL) is rare, affecting fewer than 1% of pregnancies. Most people who experience a miscarriage go on to have a successful pregnancy in the future.
When does miscarriage risk become lower?
Hearing or seeing a healthy heartbeat on ultrasound usually happens around seven weeks of pregnancy, though it can be earlier or later depending on implantation timing and development. Once a heartbeat has been detected, risk of miscarriage drops noticeably. Another major milestone is the 12-week mark: around 75% to 80% of miscarriages happen during the first trimester, so entering the second trimester means the likelihood of pregnancy loss becomes much lower.
When should you contact your healthcare team?
You should contact your healthcare team if you experience:
- Vaginal bleeding at any stage of pregnancy
- Heavy bleeding, or bleeding that becomes heavier over time
- Moderate to severe cramping or abdominal pain
- Passing blood clots or pregnancy tissue
- A sudden loss of pregnancy symptoms, particularly with bleeding or pain
- A noticeable decrease in your baby’s movements later in pregnancy, after regularly feeling movement
Some symptoms may point to an ectopic pregnancy, a medical emergency rather than a miscarriage. Seek urgent medical attention if you experience:
- Severe pain, especially on one side of your abdomen
- Pain in the tip of your shoulder
- Feeling faint or losing consciousness
- Heavy bleeding accompanied by severe pain
For many people, a miscarriage is a one-off event, and their next pregnancy progresses normally. Even after recurrent miscarriages, there is reason to be hopeful: research shows around 65 out of every 100 women with unexplained recurrent pregnancy loss go on to have a successful next pregnancy, even without special treatment.
If you’ve experienced a miscarriage, speaking with someone can help. Our counselling team is here to support you through the experience, whenever you’re ready.
Is miscarriage risk highest in the first few weeks of pregnancy?
Yes. Risk is highest in the earliest weeks general estimates range from 10% to 25% in weeks 1 to 4, while a 2025 pooled-cohort study found risk of around 4% at six weeks or earlier from the last menstrual period. Risk then declines steadily through the first trimester.
Does seeing a heartbeat on ultrasound mean the risk is gone?
No, but it is a strong positive sign. Once a healthy heartbeat is detected, usually around week seven, the risk of miscarriage drops significantly, though it does not disappear completely.
What is the miscarriage risk in the second trimester?
Risk is much lower in the second trimester around 1% to 3% between weeks 13 and 16, and under 1% between weeks 17 and 20. A 2025 pooled-cohort study found risk between weeks 13 and 19 had fallen below 0.5%.
What is the difference between a miscarriage and a stillbirth?
A miscarriage is a pregnancy loss before 20 weeks of gestation. A loss at or after 20 weeks is classified as a stillbirth.
Can lifestyle factors cause a miscarriage?
About half of all miscarriages are caused by chromosomal abnormalities that occur by chance during conception. Other contributing factors can include maternal age, certain medical conditions, uterine conditions, smoking, alcohol use, high caffeine intake, and very low or very high body weight.
Every Fertility Journey Is Different
A miscarriage does not mean you won’t go on to build the family you’ve been dreaming of. For many people, it is one chapter of their story, not the end of it. If you’re exploring donor egg treatment, Central IVF can help you access a wide range of carefully screened donor eggs through our partner clinics across Australia. Contact our team to learn more about our donor egg programs.
