Trimester by Trimester
Miscarriage Risk by Week and Maternal Age: The Real Numbers
Week-by-week and age-stratified miscarriage statistics from ACOG and the March of Dimes — plus warning signs and when to call your provider.
Clinically reviewed · June 2026
Miscarriage risk in a clinically confirmed pregnancy falls from roughly 9–10% at week 6 to under 1% by week 9, then drops again after week 12. Maternal age is the dominant driver: rates range from about 9–17% in women under 30 to more than 57% at age 45. Most early losses trace to chromosomal errors in the embryo — not anything you did.
Hearing the words "miscarriage risk" can feel heavy, especially in the early weeks when everything still feels uncertain. The truth is that the numbers are both more sobering and more reassuring than most people realize — sobering because early loss is genuinely common, reassuring because risk drops quickly with each passing week. This guide walks through what the research actually shows, week by week and age group by age group, in plain language.
This article provides general educational information, not medical advice. Talk with your OB-GYN, midwife, or maternal-fetal medicine specialist about your personal risk factors and any concerns.
How does miscarriage risk change week by week in the first trimester?
The first trimester is the highest-risk window of any pregnancy, and for good biological reason: it is when the embryo builds every major organ system from scratch. Any disruption to that extraordinarily complex process — most often a chromosomal error in the embryo itself — can end the pregnancy. The March of Dimes estimates that approximately 80% of all miscarriages occur before week 12, with the majority concentrated in the first eight weeks.
The best available week-by-week data from published cohort studies, as summarized by Medical News Today, show the following approximate rates for clinically confirmed pregnancies:
| Gestational Week | Approximate Miscarriage Rate | What is happening developmentally |
|---|---|---|
| Week 6 | ~9.4% | Primitive heart tube pulsing; neural tube formation underway; placenta developing |
| Week 7 | ~4.2% | Limb buds, early circulatory system; heartbeat visible on transvaginal ultrasound |
| Week 8 | ~1.5% | All major organ systems present; embryo transitions to "fetus"; umbilical cord fully functional |
| Week 9 | ~0.5% | Heartbeat audible via Doppler; muscles and teeth buds forming |
| Weeks 10–13 | <1% | Fingers individuated; bone calcification; liver producing bile |
| Weeks 14–20 | ~1–5% | Second trimester; most organ development complete |
The sharp decline between weeks 6 and 9 is one of the most clinically meaningful trends in early pregnancy. Once a heartbeat is confirmed by ultrasound at eight weeks and the pregnancy has progressed to week 10, the ongoing risk is low for most women without additional risk factors.
It is worth noting that these rates apply to clinically confirmed pregnancies — those identified before or around the time of a missed period. When very early chemical pregnancies (losses before a positive test is recorded) are included, some research places the total figure above 30%. Most of those losses go unrecognized as pregnancies, experienced as a late or unusually heavy period.
How does maternal age change the miscarriage odds — at every age?
If gestational week tells you how much risk you carry right now, maternal age tells you the underlying baseline you started from. The relationship between age and miscarriage risk is steep, consistent across populations, and largely biological.
ACOG data on early pregnancy loss and Cleveland Clinic's advanced maternal age guidance together describe the following approximate miscarriage probability by age group:
| Maternal Age | Approximate Miscarriage Risk | Context |
|---|---|---|
| Under 30 | 9–17% | Lowest baseline risk; egg quality is generally highest in this window |
| Age 35 | ~20% | The threshold often called "advanced maternal age"; risk begins rising meaningfully |
| Age 40 | 33–40% | One in three pregnancies; increased chromosomal error rates |
| Age 45 and above | 57–80%+ | Chromosomal abnormalities found in the vast majority of losses at this age |
Why does age drive risk so dramatically? The answer lies in chromosomes. A landmark 2024 peer-reviewed study of 7,118 miscarriage cases published in MDPI Cells found chromosomal abnormalities in 67.25% of all miscarriage specimens. The rate of chromosomal errors increased by approximately 0.7% per year of maternal age between ages 23 and 37, then accelerated to 2.1% per year between ages 38 and 44. At age 38, the abnormality rate surged by 14.79% in a single year. By age 44, 94% of miscarried pregnancies carried chromosomal defects.
Older eggs — which have been in a suspended state of cell division since before birth — are more prone to errors when they complete their division at ovulation. These errors, primarily trisomies (extra chromosomes), typically result in embryos that cannot develop normally. Most are eliminated by the body in early miscarriage, which is a biological protective mechanism rather than a failure of the body to sustain a pregnancy.
ACOG notes that autosomal trisomies account for 30–61% of chromosomally abnormal miscarriages, followed by triploidy (11–13%) and monosomy X (10–15%). Prenatal genetic counseling and options like preimplantation genetic testing (PGT-A) in an IVF cycle are available to women with recurrent loss or advanced maternal age who want to understand chromosomal status before transfer or further along in a naturally conceived pregnancy.
While chromosomal errors account for most early losses, research has identified several modifiable contributors worth discussing with your provider. A 2024 scoping review in Children (MDPI) found a significant link between progesterone deficiency and first-trimester miscarriage across all 23 included studies. Separately, a systematic review in Fertility and Sterility (Tamblyn et al., 2022; n = 7,663) found women with vitamin D deficiency had 94% higher odds of miscarriage than those who were vitamin D replete. Neither finding means you caused a miscarriage if levels were low — but both are testable and addressable in a subsequent pregnancy workup.
What are the warning signs of miscarriage — and when do you call?
Knowing when to reach out to your provider can feel anxiety-provoking, especially in the early weeks when some spotting and cramping can be normal. The key is knowing which symptoms represent a genuine signal.
Call your provider promptly if you experience:
- Any vaginal bleeding or spotting, regardless of quantity. Light spotting can be normal (implantation bleeding, cervical sensitivity), but it warrants evaluation to rule out more serious causes.
- Cramping or abdominal pain that is persistent, worsening, or severe — especially if it is accompanied by bleeding.
- Passing of clots, tissue, or fluid from the vagina. If possible and you feel comfortable doing so, your provider may ask you to bring a sample in a clean container.
- Sudden marked decrease in pregnancy symptoms, particularly nausea and breast tenderness disappearing abruptly rather than gradually. Gradual improvement as you approach weeks 10–14 is normal; a sudden drop is less so.
- Fever or foul-smelling discharge in combination with any of the above.
Seek emergency care immediately for:
- Severe one-sided abdominal or pelvic pain — this can indicate an ectopic pregnancy, which is a medical emergency requiring urgent treatment.
- Shoulder-tip pain (felt at the top of the shoulder), which can signal internal bleeding from a ruptured ectopic.
- Fainting, dizziness, or difficulty staying conscious.
- Persistent vomiting with inability to keep any fluids down for more than 12–24 hours.
The guidance above comes from the March of Dimes miscarriage resource and medical guidance from the Fertility Road summary of clinical protocols. If you are ever uncertain, err on the side of calling — your provider would rather reassure you than have you wait.
What should you know if you have had more than one miscarriage?
Experiencing a miscarriage is common — it affects roughly 10–20% of clinically confirmed pregnancies. One loss, while devastating, does not predict future losses for the majority of women. However, recurrent pregnancy loss (RPL), defined by ACOG as two or more consecutive pregnancy losses, occurs in approximately 2–5% of women who are trying to conceive.
After three consecutive losses, the risk of a further miscarriage rises to approximately 43%. ACOG recommends an evaluation workup after two or more losses — and after a single loss in women over 35 — to screen for identifiable and often treatable underlying causes:
- Uterine anatomy: a septate uterus, fibroids that impinge on the cavity, or adhesions can prevent successful implantation or early placentation.
- Antiphospholipid antibody syndrome (APS): an autoimmune condition that promotes blood clotting in placental vessels; it is treatable with low-dose aspirin and heparin.
- Parental chromosomal rearrangements: balanced translocations that produce unbalanced embryos; identified by parental karyotype.
- Thyroid and metabolic disorders: subclinical hypothyroidism and uncontrolled thyroid disease are associated with increased loss rates and are readily managed.
- Progesterone insufficiency: where luteal-phase defect or early-pregnancy progesterone levels are low, micronized progesterone supplementation is supported by FIGO (2023) and Cochrane (2025) evidence for women with recurrent loss and first-trimester bleeding.
Most causes of recurrent pregnancy loss are identifiable. If you have experienced two or more losses, asking your provider specifically for a recurrent pregnancy loss workup is a reasonable and well-supported next step.
Frequently asked
What is the miscarriage rate at 6 weeks pregnant?
At 6 weeks of pregnancy, the miscarriage rate for a clinically confirmed pregnancy is approximately 9.4%, according to cohort data cited by Medical News Today. This is among the highest weekly rates in the first trimester because the embryo's most critical organ systems — the neural tube, the primitive heart, and the placenta — are still forming, making this a window of significant biological vulnerability. The risk drops markedly in the days that follow: to about 4.2% at week 7, 1.5% at week 8, and below 1% by week 9. A heartbeat confirmed by ultrasound at 6 weeks is a reassuring sign, but it does not eliminate all risk. Most providers offer a repeat scan at 8–10 weeks before the nuchal translucency window to confirm ongoing viability. This is general information, not medical advice — speak with your provider about your individual risk.
How does miscarriage risk change week by week in the first trimester?
Risk declines steeply as the first trimester progresses. Published cohort data cited by Medical News Today show the following approximate rates for clinically confirmed pregnancies: week 6 — 9.4%, week 7 — 4.2%, week 8 — 1.5%, week 9 — 0.5%. After week 12, the risk drops to 1–5% for the period between weeks 14 and 20. The steep early-trimester decline reflects the completion of the most vulnerable stages of organogenesis and the establishment of stable placental function. ACOG notes that approximately 80% of all miscarriages occur before week 12, and the majority of those happen in the first eight weeks. Once you cross the 12-week mark with a healthy fetal heartbeat, your risk is substantially lower, though not zero. This information is educational, not a substitute for clinical guidance.
How does maternal age affect miscarriage risk?
Maternal age is the single strongest independent predictor of miscarriage risk. ACOG data indicate the following approximate rates: 9–17% for women aged 20–30; about 20% at age 35; 33–40% at age 40; and 57–80% or higher at age 45 and above. The driving mechanism is chromosomal: a 2024 peer-reviewed study of 7,118 miscarriage specimens published in MDPI Cells found chromosomal abnormalities in 67.25% of all cases, with the rate increasing by approximately 0.7% per year of maternal age between ages 23–37, and by 2.1% per year between ages 38–44. By age 44, 94% of miscarried pregnancies carried chromosomal defects. Older eggs are more prone to errors during division, leading to aneuploid embryos that cannot sustain a viable pregnancy. Speak with your OB-GYN or a genetic counselor about your individual age-related risk.
What are the warning signs of a miscarriage I should call my provider about?
Contact your obstetric provider promptly if you experience any of the following during the first trimester: vaginal bleeding or spotting of any amount; cramping or severe abdominal or low-back pain; passing of clots, tissue, or fluid from the vagina; foul-smelling discharge; or fever alongside any of the above, according to guidance from the March of Dimes. A sudden and marked decrease in pregnancy symptoms — such as nausea and breast tenderness disappearing abruptly — may also warrant a call, though symptom fluctuation is common in normal pregnancies. Seek emergency care immediately for severe one-sided abdominal pain, shoulder-tip pain, fainting, or persistent vomiting with inability to keep fluids down, as these can signal an ectopic pregnancy, which is a medical emergency. When in doubt, call your provider — that is what they are there for.
What causes most first-trimester miscarriages?
The majority of first-trimester miscarriages are caused by chromosomal abnormalities in the embryo — errors in chromosome number or structure that occur at or shortly after fertilization. ACOG states that approximately 50% of early pregnancy losses are attributable to chromosomal abnormalities, with that figure rising to more than 50% in women over 40. Autosomal trisomies — extra copies of chromosomes — account for 30–61% of chromosomally abnormal losses, followed by triploidy (11–13%) and monosomy X (10–15%). Beyond chromosomes, research published in Children (MDPI) has linked progesterone insufficiency to recurrent first-trimester loss through failure to maintain the uterine lining and regulate immune tolerance of the embryo. Anatomical factors, thyroid imbalance, and antiphospholipid antibody syndrome are other recognized contributors, particularly in recurrent loss. Most single miscarriages do not indicate an ongoing fertility problem; evaluation is typically recommended after two or more consecutive losses.
Is miscarriage risk higher with recurrent pregnancy loss?
Yes. While approximately 2–5% of women experience recurrent miscarriage (two or more consecutive losses), the risk of a subsequent loss rises meaningfully with each one. After three consecutive miscarriages, the risk of a further loss increases to approximately 43%, according to data cited by Fertility Road. ACOG recommends evaluation for underlying causes — including uterine structural anomalies such as a septate uterus or fibroids, antiphospholipid antibody syndrome, parental chromosomal rearrangements, and thyroid or metabolic disorders — after two or more losses, particularly in women over 35. Evaluation can identify treatable causes and guide management in a subsequent pregnancy. If you have experienced more than one loss, ask your provider for a recurrent pregnancy loss workup; most causes are identifiable and many are addressable.