Around 30% of pregnancies (including unrecognised pregnancies) and 1 in 8 known pregnancies end in miscarriages, defined as the spontaneous loss of pregnancy before 24 weeks of gestation. Most miscarriages tend to occur in the first trimester. Miscarriage commonly presents with vaginal bleeding ± lower abdominal pain.

Chromosomal abnormalities are the major cause of first trimester miscarriages, but in many cases, the cause is unknown. About 1% of the population have recurrent miscarriages (3 or more consecutive miscarriages).


Miscarriages can be classified as follows:
  • Early miscarriage: < 13 weeks
  • Late miscarriage: 13-24 weeks

Miscarriages are also classified based on their clinical presentation and physical examination findings (pelvic and speculum examination).

Complete miscarriage
  • Both fetus and all pregnancy tissue have been expelled from the uterus
  • Bleeding stops and further treatment is not needed

Incomplete miscarriage
  • Fetus and parts of the membranes are expelled from the uterus
  • Placenta is not fully expelled and bleeding persists
  • Surgical management is often needed to remove the remaining products of conception

Missed miscarriage
  • Usually identified via ultrasound with a small for dates uterus
  • Fetus in the uterus that did not develop or has died
  • Often do not have typical clinical symptoms of pain or vaginal bleeding

Threatened miscarriage
  • Viable pregnancy with symptoms (such as vaginal bleeding) and a closed cervical os
  • 75% of threatened miscarriages will settle
  • Carry a higher risk of preterm delivery and preterm rupture of membranes

Inevitable miscarriage
  • Non-viable pregnancy with vaginal bleeding and an open cervical os
  • Progresses to an incomplete or complete miscarriage

Recurrent miscarriage
  • Occurs in 1% of patients
  • 3 or more consecutive miscarriages
  • Offered a referral for further investigation


  • Incidence: 350.00 cases per 100,000 person-years
  • Peak incidence: 30-40 years
Condition Relative
Ruptured ovarian cysts0.14
Ectopic pregnancy0.11
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+


In most cases, there is no identifiable cause for the miscarriage.

Some known causes of miscarriages include abnormal fetal development, maternal conditions, and uterine abnormalities.

Abnormal fetal development

Chromosomal and structural abnormalities have been identified after analysing pregnancy tissue from miscarriages. Chromosomal abnormalities are a common cause of first trimester miscarriages. Other genetic abnormalities have been identified that lead to problems in the development of the placenta or embryo.

Maternal conditions

Pre-existing conditions of the woman may be the cause for miscarriages.
  • Infections such as bacterial vaginosis have been identified to be associated with late miscarriages.
  • Antiphospholipid syndrome is present in 15% of women who experience recurrent miscarriages, in particular first trimester miscarriages.
  • Thrombophilia (factor V Leiden, prothrombin gene mutation) is another identified cause of recurrent miscarriages, commonly second trimester miscarriages.
  • Endocrine problems such as polycystic ovarian syndrome, thyroid disease, diabetes mellitus, and hyperprolactinaemia may also lead to miscarriages.
  • Genetic abnormalities in the parents may also lead to miscarriages. About 2-5% of miscarriages have been identified to have parents with chromosomal abnormalities.

Uterine conditions

Anatomical or structural abnormalities of the uterine may also cause miscarriages to occur.
  • Uterine abnormalities including septate, bicornuate, or acute uterus can affect the development of the growing fetus, making it incompatible for a viable pregnancy.
  • Cervical incompetence does not allow the normal development of the fetus.
  • Fibroids typically do not affect pregnancies, but a uterus may be distorted by fibroids to the extent that it is unable to accommodate the development of a healthy fetus.

Further miscarriages

Two identified risk factors of having another miscarriage are an increase in maternal age and previous miscarriages. There is a decline in the number and quality of the oocytes as women age.
  • There is a 93% risk of miscarriage in women aged 45 and older.
  • After three consecutive miscarriages, there is a 40% risk of a further miscarriage.

Other risk factors

Other risk factors for miscarriages include:
  • Environmental factors
    • High dose radiation
    • Heavy metal exposure
  • Paternal factors
    • Tight clothing (bottom) in males
    • Sperm abnormalities
    • Old paternal age
  • Lifestyle factors
    • Smoking
    • Stress
    • Obesity


A miscarriage occurs when the pregnancy isn't viable due to numerous reasons.

Vaginal bleeding is caused by
  • Haemorrhage in the decidua basalis leading to necrosis and inflammation
  • Ovum is unable to continue to develop in the uterus
    • Initiates uterine contractions
    • Cervix begins to dilate causing the loss of fetus and pregnancy tissue.

If this occurs early prior to 12 weeks, a complete miscarriage is more likely as the placenta is unlikely to have been independently developed, thus being expelled together with the fetus.

If this occurs between 12-24 weeks, the gestation sac is more likely to rupture and the fetus then expelled while parts of the placenta remain in the uterus, classified as an incomplete miscarriage.

Clinical features

The clinical features of miscarriages vary based on what category of miscarriage it is. A missed miscarriage often does not present with any symptoms while other types of miscarriages often present with signs and symptoms.

Clinical features
  • Vaginal bleeding
    • Vary from brownish light spotting to heavy bright-red blood with clots
    • Occurs in 20-30% of pregnant women in the first trimester, where a prospective study showed that 12% of these women then had an early miscarriage.
  • Lower abdominal cramping pain
  • Vaginal fluid discharge/tissue discharge
  • Loss of pregnancy symptoms (eg. No more nausea/breast tenderness)
  • Lower back pain

Referral criteria

Patients should be referred based on their presenting signs and symptoms and urgency of the situation.
  • Immediate admission to hospital
    • Any sign of haemodynamic instability
  • Immediate admission to early pregnancy assessment unit (EPAU) or out-of-hours gynaecology unit
    • Suspicion of ectopic pregnancy
  • Referred to EPAU or out-of-hours gynaecology unit
    • Symptoms that indicate an early pregnancy problem (excluding abdominal pain, pelvic tenderness, cervical motion tenderness) and is > 6 weeks pregnant or unknown gestation
    • Any doubt of viability of the pregnancy

If the patient presents with bleeding but no pain and is < 6 weeks pregnant, expectant management should be considered.
  • Repeat pregnancy test after 7-10 days
    • Negative pregnancy test: miscarriage
    • Positive pregnancy test with persistent symptoms: referred to an EPAU or out-of-hours gynaecology unit

All women who have been referred to an EPAU should be followed up with the appropriate support afterwards.

All women who have experienced recurrent miscarriages should be offered a referral to a specialist gynaecologist clinic to further investigate the cause.


Miscarriage is often suspected by its clinical presentation and confirmed by further investigation.

The most common investigation done is a transvaginal ultrasound scan to determine the location and viability of the pregnancy. If unable to determine the status of the fetus, a repeat scan will be done after a minimum of 7 days.

Other investigations that can be used are repeat serum beta-human chorionic gonadotropin (bhCG) levels to determine the trend of the hormone levels. bhCG levels will decrease after a miscarriage as it is produced by the placenta.

If an ectopic pregnancy as a differential diagnosis is suspected, a laparoscopy may be done.

Recurrent miscarriages are further investigated to identify any underlying cause. These investigations include:
  • Karyotyping to identify chromosomal abnormalities
  • Transvaginal ultrasound scans to identify structural or anatomical abnormalities
  • Blood tests
    • Antiphospholipid antibodies
    • Lupus anticoagulant

Differential diagnosis

Vaginal bleeding and abdominal pain in early pregnancy have numerous differential diagnoses. Ectopic pregnancy is the most important differential diagnosis to rule out as it is a medical emergency.

Pregnancy-related differential diagnoses:
  • Ectopic pregnancy
    • Similarities: vaginal bleeding and lower abdominal pain
    • Differences: pain is usually unilateral, more severe, and before bleeding presents. The bleeding in an ectopic pregnancy also tends to be darker and less heavy. There is also cervical excitation in ectopic pregnancy.
  • Molar pregnancy
    • Similarities: vaginal bleeding and abdominal pain.
    • Differences: heavy and prolonged bleeding with clots ± brown watery vaginal discharge. The uterus is large for its gestational dates. There are exaggerated symptoms of pregnancy such as extreme morning sickness.
  • Ruptured ovarian corpus luteum cyst
    • Unilateral peritonitic abdominal pain ± vaginal bleeding
  • Ovarian torsion
    • Palpable adnexal or pelvis mass with pelvic pain ± vaginal bleeding
  • Fibroid degeneration
    • Abdominal pain ± vaginal bleeding, fever, abdominal swelling

Non-pregnancy-related differential diagnoses:
  • Cervical pathology
    • Cervicitis: inflammation of the cervix may cause vaginal bleeding
    • Cervical ectropion: presents with spotting and pain commonly during or after intercourse
    • Cervical polyps: presents with intermenstrual spotting, bleeding after intercourse, heavier period flow, and vaginal discharge
    • Cervical trauma: may cause bleeding
  • Cancers: all may present with bleeding
    • Cervical cancer
    • Vulval cancer
    • Vaginal cancer
  • Haemorrhoids: may cause bleeding that is mistaken to be vaginal bleeding


In the 2019 NICE guidelines, 3 types of management for miscarriage were discussed:

Expectant management
  • 'Waiting for a spontaneous miscarriage'
  • First-line and involves waiting for 7-14 days for the miscarriage to complete spontaneously
  • If expectant management is unsuccessful then medical or surgical management may be offered

Some situations are better managed with medically or surgically. NICE list the following:
  • increased risk of haemorrhage
    • she is in the late first trimester
    • if she has coagulopathies or is unable to have a blood transfusion
  • previous adverse and/or traumatic experience associated with pregnancy (for example, stillbirth, miscarriage or antepartum haemorrhage)
  • evidence of infection.

Medical management:
  • 'Using tables to expedite the miscarriage'
  • Vaginal misoprostol
    • Prostaglandin analogue, binds to myometrial cells to cause strong myometrial contractions leading to the expulsion of tissue
  • The addition of oral mifepristone is not currently recommended by NICE in contrast to US guidelines
  • Advise them to contact the doctor if the bleeding hasn't started in 24 hours.
  • Should be given with antiemetics and pain relief

Surgical management
  • 'Undergoing a surgical procedure under local or general anaesthetic'
  • The two main options are vacuum aspiration (suction curettage) or surgical management in theatre
  • Vacuum aspiration is done under local anaesthetic as an outpatient
- Surgical management is done in theatre under general anaesthetic. This was previously referred to as 'Evacuation of retained products of conception'


There are some complications that may occur after having a miscarriage.
  • Incomplete miscarriage
    • Retained products of conception
    • May require medical or surgical intervention
  • Haemorrhagic shock
    • Due to excessive bleeding
    • Medical emergency that needs replacement of blood lost
  • Infection
    • 3% of women
    • Due to retained pregnancy tissue in the uterus
  • Psychological complications
    • Depression/anxiety
    • Follow-up should be arranged
  • Haemolytic disease of the newborn
    • Give anti-D immunoglobulin to rhesus-negative women who have had surgical intervention for their miscarriage
    • Do not give anti-D immunoglobulin to women who have only had medical management, a threatened, or complete miscarriage
  • Increased risk of having another miscarriage
    • 40% risk of a future miscarriage after three consecutive miscarriages