# 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.

*Published 2026-06-25 · By Maya Ellison, CNM*

The short answer
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](https://www.marchofdimes.org/find-support/topics/miscarriage-loss-grief/miscarriage), 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](https://www.medicalnewstoday.com/articles/322634), show the following approximate rates for clinically confirmed pregnancies:

  Approximate miscarriage rates by gestational week (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](https://www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2018/11/early-pregnancy-loss) and [Cleveland Clinic's advanced maternal age guidance](https://my.clevelandclinic.org/health/diseases/22438-advanced-maternal-age) together describe the following approximate miscarriage probability by age group:

  Approximate miscarriage risk by maternal age (ACOG/Cleveland Clinic)

      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](https://www.mdpi.com/2073-4409/14/1/8) 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.

A note on modifiable risk factors
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](https://www.marchofdimes.org/find-support/topics/miscarriage-loss-grief/miscarriage) 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.

## Sources

1. [Early Pregnancy Loss](https://www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2018/11/early-pregnancy-loss)
2. [Miscarriage](https://www.marchofdimes.org/find-support/topics/miscarriage-loss-grief/miscarriage)
3. [Miscarriage rates by week: Risks and statistics](https://www.medicalnewstoday.com/articles/322634)
4. [Chromosomal Abnormalities in Miscarriages and Maternal Age: New Insights from the Study of 7118 Cases](https://www.mdpi.com/2073-4409/14/1/8)
5. [Vitamin D and miscarriage: a systematic review and meta-analysis](https://www.sciencedirect.com/science/article/pii/S0015028222002588)
6. [Exploring Progesterone Deficiency in First-Trimester Miscarriage and the Impact of Hormone Therapy on Foetal Development: A Scoping Review](https://pmc.ncbi.nlm.nih.gov/articles/PMC11049201/)
7. [Miscarriage Statistics 2026: Causes, Rates, Psychological Impact](https://fertilityroad.com/treatment-options-abroad/miscarriage-statistics/)
8. [Advanced Maternal Age: Pregnancy After 35](https://my.clevelandclinic.org/health/diseases/22438-advanced-maternal-age)

---
Source: https://natalnew.com/trimesters/first-trimester-miscarriage-risk-by-week
Index: https://natalnew.com/llms.txt · Full text: https://natalnew.com/llms-full.txt