Summary

Miscarriage is the spontaneous loss of pregnancy before viability, defined as before 24 weeks gestation in the UK (before 20 weeks in some countries). It affects 10-20% of clinically recognised pregnancies and is the most common complication of early pregnancy. The vast majority (80%) occur in the first trimester. Women presenting with vaginal bleeding in early pregnancy require careful assessment to determine the type of miscarriage, exclude ectopic pregnancy, and provide appropriate management. [1,2]

Key Facts

• Definition: Loss of pregnancy before 24 weeks gestation (UK) or before 20 weeks (USA).
• Incidence: 10-20% of clinically recognised pregnancies; higher if biochemical pregnancies included. [3]
• Recurrence: Single miscarriage = 20% risk next pregnancy; 3 consecutive = 30-40% risk.
• Timing: 80% occur in first trimester (less than 12 weeks).
• Cause: 50-60% are due to chromosomal abnormalities (primarily trisomies).
• Terminology: "Miscarriage" is the preferred patient-facing term; "spontaneous abortion" is clinical/ICD terminology.

Clinical Pearls

Rule Out Ectopic First: Before diagnosing any type of intrauterine miscarriage, you must determine pregnancy location. An "incomplete miscarriage" diagnosis is dangerous if the pregnancy is actually ectopic.

Cervical Shock: Products of conception impacted in the cervical os cause vagal stimulation → bradycardia, hypotension, pallor. Treatment is IMMEDIATE removal of products from the os with sponge forceps.

Empty Uterus = Not Reassurance: An empty uterus on ultrasound with a positive pregnancy test may be: complete miscarriage, ectopic pregnancy, or very early intrauterine pregnancy. Serial β-hCG and follow-up scan are essential.

Anti-D Immunoglobulin: Give to all Rh-negative women with threatened, inevitable, incomplete, or missed miscarriage greater than 12 weeks, or any surgical/medical management.

Types of Miscarriage - Summary Table

Detailed Descriptions

Threatened Miscarriage

• Definition: Bleeding with viable intrauterine pregnancy.
• Presentation: Light vaginal bleeding, minimal pain, closed cervix.
• Ultrasound: Viable fetus (cardiac activity present).
• Prognosis: 50-75% continue to full-term delivery. [5]
• Management: Reassurance, avoid strenuous activity, follow-up scan in 1-2 weeks.

Inevitable Miscarriage

• Definition: Cervix is open, miscarriage will occur.
• Presentation: Heavy bleeding, significant cramping, os open.
• Ultrasound: Products in lower segment or cervix.
• Management: Cannot be prevented; expedite with medical or surgical management.

Incomplete Miscarriage

• Definition: Some products expelled, some retained.
• Presentation: Heavy bleeding, cramping, os may be open or closed.
• Ultrasound: Heterogeneous tissue greater than 15mm in endometrial cavity.
• Risk: Continued bleeding, infection.
• Management: Medical (misoprostol) or surgical (MVA/SMM).

Complete Miscarriage

• Definition: All products of conception expelled.
• Presentation: Bleeding settling, pain resolved, os closed.
• Ultrasound: Empty uterus or endometrial thickness less than 15mm.
• β-hCG: Declining.
• Management: Confirm completeness, emotional support, contraception.

Missed Miscarriage (Early Fetal Demise/Anembryonic Pregnancy)

• Definition: Non-viable pregnancy with retained products, no active bleeding.
• Types:
  • Early Fetal Demise: Embryo present but no cardiac activity.
  • Anembryonic Pregnancy: Gestational sac without embryo development.
• Presentation: Often asymptomatic; discovered on routine scan.
• Ultrasound Criteria (NICE):
  • CRL greater than or equal to 7mm with no heartbeat.
  • Mean sac diameter greater than or equal to 25mm with no embryo visible.
• Management: Expectant (2-3 week wait), medical, or surgical.

Septic Miscarriage

• Definition: Miscarriage complicated by uterine infection.
• Risk Factors: Retained products, unsafe abortion, instrumentation.
• Presentation: Fever, tachycardia, offensive vaginal discharge, uterine tenderness.
• Organisms: Polymicrobial; E. coli, anaerobes, Group A Strep.
• Management: IV broad-spectrum antibiotics + URGENT surgical evacuation.

General Assessment

• Vital signs: Pulse, BP (assess for shock).
• Pallor, distress level.
• Temperature (fever suggests infection).

Abdominal Examination

• Tenderness (usually suprapubic).
• Uterine size (may be smaller than dates in missed miscarriage).
• Peritonism (suggests ectopic with bleeding).

Speculum Examination

Purpose

• Visualise cervix and os.
• Identify source of bleeding.
• Remove products from os if causing cervical shock.

Findings

Bimanual Examination

• Cervical motion tenderness (think ectopic).
• Uterine size.
• Adnexal mass (ectopic, corpus luteum cyst).

Prognosis After Single Miscarriage

• Risk of next pregnancy miscarriage: 20% (same as baseline).
• 85% of women will have successful subsequent pregnancy.
• No investigations or treatment needed after single miscarriage.

Prognosis After Recurrent Miscarriage (3+)

• Overall subsequent live birth rate: 60-75%.
• With antiphospholipid syndrome (treated): 70-80% success.
• Unexplained recurrent miscarriage: 75% success with supportive care only.

Time to Next Pregnancy

• WHO previously recommended 6-month wait (no evidence).
• Current evidence: Conception within 3 months of miscarriage has better outcomes than waiting longer. [7]
• Psychologically: Try when emotionally ready.

Follow-Up Recommendations

Key Guidelines

Landmark Studies

1. MIST Trial (2006) [6]

• Question: Expectant vs medical vs surgical for incomplete/missed miscarriage?
• N: 1,200 women.
• Result: All three effective; no difference in infection or subsequent fertility.
• Impact: Established patient choice as central to management.
• PMID: 16627509.

2. Quenby et al. (2021) [8]

• Question: Does progesterone prevent miscarriage in threatened miscarriage?
• N: PRISM trial, 4,153 women.
• Result: Vaginal progesterone reduced miscarriage in women with previous losses; no benefit in those without.
• Impact: Progesterone offered to women with threatened miscarriage and history of loss.
• PMID: 33164751.

3. Love et al. (2010) [7]

• Question: Optimal interpregnancy interval after miscarriage?
• N: 30,937 women.
• Result: Conception within 6 months had lowest risk of subsequent miscarriage.
• Impact: No evidence to delay conception.
• PMID: 20688838.

4. PROMISE Trial (2015)

• Question: Does progesterone prevent recurrent miscarriage?
• N: 826 women with recurrent miscarriage.
• Result: No overall benefit (but subgroup may benefit).
• Impact: Progesterone not routine for recurrent miscarriage.
• PMID: 26586795.

What is a Miscarriage?

A miscarriage is the loss of a pregnancy before 24 weeks. Most happen in the first 12 weeks. Miscarriages are very common - about 1 in 5 confirmed pregnancies ends in miscarriage.

Why Does Miscarriage Happen?

• Most miscarriages (over half) happen because of chromosome problems in the developing baby that happened by chance.
• It is NOT caused by anything you did - exercise, work, sex, or stress do not cause miscarriage.
• Sometimes the cause is not known.

What Are the Warning Signs?

• Vaginal bleeding (spotting to heavy).
• Cramping or pain in your lower tummy or back.
• Passing tissue or clots.
• Pregnancy symptoms (nausea, breast tenderness) reducing suddenly.

What Happens Next?

If you have bleeding in early pregnancy, you may be offered:

• Ultrasound scan: To check if the pregnancy is healthy.
• Blood tests: To check pregnancy hormone levels.
• Follow-up scan: Sometimes a second scan is needed a week later to be certain.

How is Miscarriage Managed?

There are three options, and you can usually choose:

Expectant (Wait and Watch)

• Let your body pass the pregnancy naturally.
• Can take 1-4 weeks.
• You'll have a pregnancy test in 3 weeks to confirm it's complete.

Medical (Tablets)

• A tablet called misoprostol helps your body pass the pregnancy.
• Usually works within a few days.
• Causes cramping and bleeding.

Surgical

• A small procedure to remove the pregnancy tissue.
• Done under local or general anaesthetic.
• Quick and effective.

What About Future Pregnancies?

• Most women who have a miscarriage go on to have a healthy pregnancy next time.
• You can try again when you feel ready - there's no need to wait.
• If you have three miscarriages in a row, you may be referred for specialist tests.

When to Seek Urgent Help

• Very heavy bleeding (soaking more than 1 pad per hour).
• Severe pain.
• Fever or feeling very unwell.
• Dizziness or fainting.
• Shoulder tip pain (could indicate ectopic pregnancy).

Support

• The Miscarriage Association: miscarriageassociation.org.uk
• Tommy's: tommys.org
• Sands (if late miscarriage): sands.org.uk