Miscarriage
Miscarriage, also known as early pregnancy loss or spontaneous abortion, refers to spontaneous pregnancy loss before 24 weeks of gestation.
This updated UKMLA guide to miscarriage is based primarily on NICE NG126, which covers causes, symptoms, referral criteria, diagnosis, and management.
Definition
Miscarriage refers to spontaneous pregnancy loss before 24 weeks of gestation.
The terms “miscarriage,” “early pregnancy loss,” and “spontaneous abortion” are used interchangeably.
Stillbirth is a closely related term, referring to fetal death / pregnancy loss from 24 weeks of gestation onwards, where the baby is born with no signs of life.
Causes and Risk Factors
>60% of miscarriages during 6-10 weeks of gestation are believed to be caused by abnormal fetal chromosomes (e.g. trisomies) [Ref]
Most common risk factor: advanced maternal age [Ref]
- Incidence at 20-30 y/o: 9-17%
- Incidence at 45 y/o: 75-80%
- NHS states maternal age >35 y/o and paternal age >45 y/o as a risk factor [Ref]
Other risk factors: [Ref]
| Obstetric factors |
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| Chronic medical conditions |
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| Infections |
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| Structural causes |
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| Modifiable risk factors |
|
Clinical Features
~80% of miscarriages occur within the 1st trimester
Non-specific clinical features:
- Vaginal bleeding
- Uterine cramping / pain
A miscarriage can be asymptomatic (missed miscarriage). It may only be notable due to the regression of common signs and symptoms of pregnancy, or when a pregnancy test turns -ve. [Ref]
More details on the types of miscarriage are discussed in the diagnosis section below.
Diagnosis
Referral Criteria
| Scenario | Referral recommendations | Rationale |
|---|---|---|
+ve Pregnancy test PLUS any of the following:
|
Immediate referral to early pregnancy assessment service (or out-of-hours gynaecology service) | Possible ectopic pregnancy |
Vaginal bleeding PLUS any of the following:
|
Refer to early pregnancy assessment service (or out-of-hours gynaecology service)
Urgency depends on clinical judgement |
Possible ectopic pregnancy or miscarriage |
Offer expectant management (instead of referring immediately) if ALL the following apply (low risk of ectopic pregnancy):
- <6 weeks of gestation
- PAINLESS bleeding
- No risk factors (e.g. previous ectopic pregnancy)
Expectant management involves:
- Safety netting – to return if bleeding continues or pain develops
- Repeat urine pregnancy test after 7-10 days, and return if +ve
Diagnostic Approach
Initial investigations (after clinical history and examination): [Ref]
- Serum β-hCG testing (does NOT diagnose miscarriage alone)
- Definitive test: TVUSTrans-vaginal ultrasound
If the initial hCG testing and ultrasound are inconclusive → perform serial β-hCG testing
- A decrease in >50% after 48 hours is supportive of a miscarriage
Types of Miscarriage – Diagnosis and Recognition
Disclaimer: By definition, miscarriage refers to a non-viable pregnancy / pregnancy loss before 24 weeks.
- Threatened miscarriage is technically not a true miscarriage, as the pregnancy remains viable.
- However, traditional teaching and most textbooks group all of these under “types of miscarriage.”
For clarity and exam relevance, the following classifications are presented together in line with traditional teaching. It is important to be aware that non-viability is NOT present in all types of miscarriage.
Miscarriage is subdivided into: [Ref1][Ref2]
| Miscarriage type | Description | Clinical history | Cervical os | Ultrasound findings |
|---|---|---|---|---|
| Threatened* | Pregnancy is at risk (threatened), but remains viable | Vaginal bleeding +/- mild cramping | Closed | Viable intrauterine pregnancy (fetal cardiac activity present) |
| Missed | Non-viable pregnancy in the uterus | Asymptomatic (symptoms have been “missed”) | Non-viable intrauterine pregnancy | |
| Inevitable | Pregnancy will NOT continue, and expulsion is inevitable (unavoidable) | Vaginal bleeding + cramping | Open | Intrauterine pregnancy +/- fetal cardiac activity (may be viable or non-viable)
Key point: Pregnancy will inevitably be expelled, regardless of current viability |
| Incomplete | Partial expulsion of POCProducts of conception |
Vaginal bleeding + cramping Passage of tissue / clots |
Heterogeneous material in the uterine cavity +/- endocervical canal (retained POCProducts of conception)
NO intrauterine pregnancy |
|
| Complete | Complete expulsion of POCProducts of conception | Vaginal bleeding + cramping (now resolved)
History of passage of tissue / clots |
Closed | Empty uterine cavity (no retained POCProducts of conception) |
Septic miscarriage is a complication of any type of miscarriage, characterised by infection.
In addition to the clinical features of miscarriage, additional signs include fever, uterine tenderness, purulent vaginal discharge, and signs of sepsis.
Confirming Pregnancy Viability
Test of choice: TVUSTrans-vaginal ultrasound
Ultrasonic criteria of non-viable pregnancy:
- CRLCrown-rump length ≥7 mm with no visible fetal heartbeat, or
- MSDMean sac diameter ≥25 mm with no visible fetal pole
However, NICE advises seeking a second opinion and/or repeating the scan before confirming the diagnosis
- Inform women that the diagnosis of miscarriage using 1 ultrasound scan cannot be guaranteed to be 100% accurate, and there is a small chance that the diagnosis may be incorrect, particularly at very early gestational ages
Exact ultrasound approach
The following information is included for completeness and to support understanding; they are unlikely to be examined in detail.
| Step | Ultrasound approach | Action / interpretation |
|---|---|---|
| 1 | Confirm whether there is an intrauterine pregnancy | If no intrauterine pregnancy is seen, consider a pregnancy of unknown location rather than assuming complete miscarriage
|
| 2 | Look for fetal cardiac activity (FCA) |
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| 3 | If fetal pole is visible → measure crown rump length (CRL)
If fetal pole not visible → proceed to step 4 |
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| 4 | Fetal pole not visible → measure mean sac diameter (MSD) |
|
Management
If the patient presents with haemorrhage / haemodynamic instability → urgent surgical uterine evacuation under general anaesthesia is necessary [Ref]
Septic Miscarriage
Threatened Miscarriage
As discussed above, threatened miscarriage is not a true miscarriage, as the pregnancy remains viable and may continue normally. Therefore, it is managed separately from other types of miscarriage.
Management depends on whether the patient has a history of previous miscarriage or not.
| No previous miscarriage | Offer expectant management:
|
| Yes previous miscarriage | Offer vaginal micronised progesterone
To be continued until 16 weeks of gestation |
Complete Miscarriage
No active medical or surgical interventions are necessary [Ref]
- As the complete expulsion of POCProducts of conception has already taken place
- Patient should be followed up with ultrasound +/- serial serum β-hCG measurements to confirm complete passage of POCProducts of conception
Other Miscarriages (Missed / Inevitable / Incomplete)
Approach:
- Expectant management for 7-14 days is generally 1st line for most patients
- Indications to offer non-expectant management (i.e. medical or surgical management) as 1st line:
- Expectant management is not acceptable to the patient → offer medical management
- Patient is at increased risk of haemorrhage (e.g. late first trimester)
- Patient is at increased risk from the effects of haemorrhage (e.g. coagulopathies, unable to have a blood transfusion)
- Presence of previous adverse and/or traumatic experience associated with pregnancy (e.g. stillbirth, miscarriage, antepartum haemorrhage)
Some factors might influence the decision of choosing between medical vs surgical management:
- Patient not willing to attend follow-up → surgical preferred
- Patient with medical comorbidities (e.g. severe anaemia, bleeding disorders, cardiovascular diseases) → surgical preferred (medical management carries a higher risk of significant blood loss)
Expectant Management
| Patient education at the start | Explain that expectant management involves waiting for the miscarriage to complete naturally with no medical or surgical treatment, usually over 7–14 days
Patients should be advised that:
|
| Safety-netting advice | Advise the patient to seek urgent medical help if they develop:
|
| Follow-up | If bleeding and pain settle within 7–14 days, this suggests that the miscarriage has completed.
Perform a home urine pregnancy test 3 weeks after:
If bleeding and pain do not start, or are persisting / increasing, offer a repeat ultrasound scan. |
Medical Management
| Choice of medical expulsion regimen | Depends on the type of miscarriage:
*Disclaimer: NICE only made specific recommendations on the medical management of missed and incomplete miscarriage. ACOG: medical management of inevitable miscarriage → mifepristone followed by misoprostol (similar to missed miscarriage) [Ref] |
| Supportive care | Provide analgesics and antiemetics as needed |
| Follow-up | Perform a home urinary pregnancy test 3 weeks after completion of medical management |
Surgical Management
Offer the women a choice of:
- Manual vacuum aspiration under local anaesthetic in outpatient setting, OR
- Surgical management under general anaesthetic in theatre
Offer anti-D immunoglobulin prophylaxis to all Rh-ve women who have a surgical management for miscarriage.
References
NICE Ectopic pregnancy and miscarriage: diagnosis and initial management
Related Articles
Pregnancy of Unknown Location (PUL)