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. 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. It’s much more common than many people realise, with studies showing that up to one in five recognised pregnancies end in miscarriage. Most of these happen during the first 12 weeks of pregnancy. The number is likely to be even higher, as some miscarriages happen very early and can easily be mistaken for a normal period.
As your pregnancy progresses, the chance of miscarriage becomes lower. Understanding how miscarriage risk changes throughout pregnancy, and what causes miscarriage, can help you feel more informed during this important time.
What is the miscarriage risk week by week?
Weeks 1 to 4
During the first few weeks of pregnancy, miscarriage risk is at its highest. General estimates suggest the risk is between 10% and 25% during this stage.
Many miscarriages that happen this early are known as chemical pregnancies. These occur shortly after implantation, before five weeks, and many people don’t even realise they were pregnant. What seems like a slightly heavier or later-than-usual period may actually have been a very early pregnancy loss.
Although this is upsetting for those who were trying to conceive, it’s important to remember that these early losses are usually caused by factors completely outside anyone’s control.
Weeks 5 to 8
By weeks five to eight, the risk begins to decrease as the pregnancy develops. General estimates place the risk at around 5% to 10% during this stage.
A 2008 Australian study found the chance of miscarriage was approximately 9.4% at six weeks, dropping to 4.2% by seven weeks. Around this time, many people have their first ultrasound and hear the baby’s heartbeat.
Seeing a heartbeat is a major milestone. While it doesn’t remove the risk completely, it is a very positive sign that the pregnancy is progressing well. If a heartbeat isn’t seen during the first scan, try not to panic – sometimes it’s too early. Your healthcare provider may recommend another scan a week later.
Weeks 9 to 12
The risk continues to fall throughout the remainder of the first trimester, with general estimates sitting at around 3% to 5%.
Research shows that once a healthy heartbeat has been detected on ultrasound, the chance of miscarriage drops significantly. In the same Australian study, the risk at eight weeks was around 1.5%, and it continued to decrease as the pregnancy progressed.
Weeks 13 to 20
Once you reach the second trimester, the chance of miscarriage becomes much lower. General estimates suggest the risk is around 1% to 3% between weeks 13 and 16, and less than 1% between weeks 17 and 20.
Research published in 2025 also found miscarriage rates between 14 and 19 weeks were generally between 1% and 5%. Pregnancy loss after 20 weeks is no longer called a miscarriage. Instead, it is known as a stillbirth.
What causes most miscarriages?
One of the hardest parts of miscarriage is wondering why it happened. The truth is that, 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. These genetic changes occur by chance during conception and prevent the pregnancy from developing normally. When this happens, the pregnancy is unfortunately not able to continue, regardless of anything the parents did or didn’t do.
Other factors also increase the likelihood of miscarriage, including:
- Increasing maternal age.
- Sperm-related factors, such as sperm DNA damage, chromosomal abnormalities and lifestyle factors like obesity, which can 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.
It’s also worth remembering that miscarriage is common. Studies estimate that around 15% of recognised pregnancies end in miscarriage, while experiencing three or more miscarriages in a row is rare, affecting fewer than 1% of pregnancies. Most people who experience a miscarriage will go on to have a successful pregnancy in the future.
Read: Recurrent Miscarriages? The Cause May Lie in Sperm Quality
When does miscarriage risk become lower?
Hearing or seeing a healthy heartbeat on an ultrasound usually happens around seven weeks of pregnancy. However, it may be a little earlier or later depending on when implantation occurred and your baby’s development. Research shows that once a heartbeat has been detected, the risk of miscarriage drops.
Another major milestone is reaching 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 if it’s accompanied by bleeding or pain.
- A noticeable decrease in your baby’s movements later in pregnancy, after you’ve been regularly feeling movement.
Some symptoms may point to an ectopic pregnancy, which is 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.
The reassuring news is that, for many people, a miscarriage is a one-off event, and their next pregnancy progresses normally. Even after recurrent miscarriages, there is still reason to be hopeful. Research shows that around 65 out of every 100 women with unexplained recurrent pregnancy loss go on to have a successful next pregnancy, even without special treatment.
Every fertility journey is different, but 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, we 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.
