Miscarriage

Synonym: spontaneous abortion (this term has fallen out of favour and is no longer commonly used).

Miscarriage is defined as the loss of a pregnancy before 24 weeks of gestation in the UK (though definitions vary and some countries define it as prior to 20 weeks).

Ectopic pregnancy and gestational trophoblastic disease are not included.

Types of miscarriage

• Threatened miscarriage: mild symptoms of bleeding. Usually little or no pain. The cervical os is closed.

• Inevitable miscarriage: usually presents with heavy bleeding with clots and pain. The cervical os is open. The pregnancy will not continue and will proceed to incomplete or complete miscarriage.

• Incomplete miscarriage: this occurs when the products of conception are partially expelled.

• Complete miscarriage: presents with a history of confirmed pregnancy, followed by heavy bleeding and clots; a subsequent ultrasound scan shows no pregnancy tissue in the uterine cavity.

• Missed miscarriage: the foetus is dead but retained. It may present with a history of threatened miscarriage and persistent, dark-brown discharge but may have no symptoms at all. Early pregnancy symptoms may decrease or disappear.

• Recurrent miscarriage: three or more consecutive miscarriages.

Causes of miscarriage (aetiology)

In more than 60% of miscarriages before 10 weeks of gestation, the cause is thought to be foetal chromosomal abnormalities.¹ Inflammatory and immunological dysregulation are thought also to play a role in early pregnancy loss. ²³

Risk factors for miscarriage²

Usually no underlying cause is found, but common recognised risk factors for miscarriage include:

• Advanced maternal age - the incidence of early pregnancy loss in women aged 20 to 30 years is 9 to 17%, while the incidence in women aged 45 years is 75 to 80%.

• Prior history of miscarriage - the risk increases after each loss. The risk of miscarriage in a future pregnancy is approximately 20% after one miscarriage, 28% after 2 consecutive miscarriages, and 43% after ≥3 consecutive miscarriages.

• First trimester bleeding. Between 12 and 57% of pregnancies with first trimester bleeding end in miscarriage.

• Obesity.

• Poorly controlled diabetes.

• Coeliac disease - a gluten-free diet removes the higher risk.

• Hyperprolactinaemia.

• Poorly controlled thyroid disease.

• Autoimmune conditions, such as antiphospholipid syndrome.

• Infections - this includes, but is not limited to, syphilis, parvovirus B19, Zika virus, and cytomegalovirus infections.

• Structural uterine abnormalities.

• Intrauterine pregnancies with an intrauterine device in situ.

• Chronic stress secondary to social determinants of health (for example, living with threats of violence).

• Alcohol consumption.

• Smoking.

• Cocaine use.

• High caffeine consumption.

• Environmental contaminants, including arsenic, lead, and organic solvents.

Miscarriage epidemiology

• Early pregnancy loss accounts for 50,000 hospital admissions in the UK annually⁴ and there are 44 pregnancy losses a minute worldwide.⁵

• Miscarriage occurs in 10-20% of clinically recognised pregnancies;² the true rate is higher as many may occur before a woman has realised she is pregnant. Studies which track daily beta-hCG levels have shown the miscarriage rate to be 38%.²

• The risk falls rapidly with advancing gestation:⁶

  • 9.4% at 6 complete weeks of gestation.

  • 4.2% at 7 weeks.

  • 1.5% at 8 weeks.

  • 0.5% at 9 weeks.

  • 0.7 % at 10 weeks.

Miscarriage symptoms (presentation)

• Most cases present with vaginal bleeding and pain.

• In a missed miscarriage, the woman might have very few symptoms (usually the reduction of nausea or other early pregnancy symptoms) or none at all.

• Approximately half of women with a threatened miscarriage will go on to have a complete miscarriage. This is most likely if they have bleeding that is increasing, bleeding that is heavier than a normal menstrual period or bleeding with clots.

• There are signs to look for in cases of first-trimester bleeding:

  • Is the patient shocked through blood loss? If so, immediate hospital admission is required. Pelvic and speculum examination may be indicated in a hospital setting to check for products of conception in the cervical canal or for whether the cervical os is open.

Other causes of first trimester bleeding

• Ectopic pregnancy:

  • This is the single most important diagnosis to exclude.

  • In ectopic pregnancy, the pain is usually significant, may be unilateral and usually precedes the bleeding.

  • Compared to a miscarriage, the loss is usually less heavy and darker - and there is acute pain on manipulating the cervix (cervical excitation).

• An implantation bleed (occurs when a fertilised egg embeds itself in the lining of the uterus). About one in four women will experience an implantation bleed.⁷

• Cervical polyp.

• Cervical ectropion.

• Cervicitis/vaginitis.

• Neoplasia.

• Hydatiform mole.

Diagnosis of viable intrauterine pregnancy⁴

• A transvaginal ultrasound scan identifies the location of the pregnancy and whether there is a fetal pole and heartbeat. A transabdominal ultrasound scan is more limited, particularly at early stages of pregnancy.

• More than one scan might be needed to determine the viability of the pregnancy, particularly if the first scan is at a very early gestation.

• Serum beta-hCG measurements may also be used, particularly if there is a pregnancy of unknown location.

• A woman with an increase in serum hCG levels greater than 63% after 48 hours is likely to have a developing intrauterine pregnancy (although the possibility of an ectopic pregnancy cannot be excluded).

• For a woman with a decrease in serum hCG levels greater than 50% after 48 hours, the pregnancy is unlikely to continue.

Rare causes of a raised hCG should also be borne in mind, including gestational trophoblastic disease or cranial germ cell tumour.

Miscarriage management⁴

Threatened miscarriage

Advise a woman with a confirmed intrauterine pregnancy with a fetal heartbeat who presents with vaginal bleeding, but has no history of previous miscarriage, that:

• If her bleeding gets worse, or persists beyond 14 days, she should return for further assessment.

• If the bleeding stops, she should start or continue routine antenatal care.

Women who have an intrauterine pregnancy confirmed by a scan, have vaginal bleeding and have previously had a miscarriage, should be offered vaginal micronised progesterone 400 mg twice a day. If a fetal heartbeat is confirmed, this progesterone should be continued until 16 completed weeks of pregnancy. The guidance is that this medication should be started in the early pregnancy unit because of the requirements for a scan confirming an intra-uterine pregnancy before starting treatment.

Expectant management²⁴

Expectant management for 7 to 14 days should be offered as the first-line management strategy for women with a confirmed diagnosis of miscarriage. Other management options should be considered for women at increased risk of haemorrhage, those with previous adverse or traumatic obstetric experiences, those who would be more at risk from haemorrhage or where there is evidence of infection.

If the resolution of bleeding and pain indicate that the miscarriage is likely to have been completed during 7 to 14 days of expectant management, the woman should be advised to take a urine pregnancy test after three weeks, and to return for individualised care if it is positive.

If bleeding and pain has not started or is continuing beyond 7-14 days, a repeat scan is recommended and then a further discussion about management options.

70% of first trimester miscarriages will be complete with one month and 80% within two. There is some evidence that expectant management is more successful in women with symptomatic miscarriage than those who present with a missed miscarriage.

Medical management

Evidence suggests that medical treatment, with mifepristone and misoprostol, and expectant care are both acceptable alternatives to routine surgical evacuation for incomplete miscarriage.⁸Both medications are unlicensed but recommended in guidelines.⁴

Guidelines advise the use of mifepristone 200 mg orally and then a further dose of 800mg misoprostol vaginally, orally or sublingually, for a missed miscarriage, unless the gestational sac has been passed before this second dose.

For an incomplete miscarriage, a single dose of 600 mg or 800 mg of misoprostol is recommended, either orally, vaginally or sublingually. Mifepristone is not used in this scenario.

Pain relief and anti-emetics should be used as needed. Women should repeat a pregnancy test after 3 weeks but return to the early pregnancy unit earlier if they have worsening symptoms. If their pregnancy test is positive after 3 weeks they should be re-assessed in the early pregnancy unit to rule out a retained, molar or ectopic pregnancy.

Surgical management

Where clinically appropriate, women undergoing a miscarriage should also be offered a choice of either:

• Manual vacuum aspiration under local anaesthetic in an outpatient or clinic setting.

• Surgical management in a theatre under general anaesthetic.

Anti-D rhesus prophylaxis

Anti-D rhesus prophylaxis at a dose of 250 IU (50 micrograms) should be offered to all rhesus-negative women who have a surgical procedure to manage an ectopic pregnancy or a miscarriage, but should not be offered to those women who miscarry naturally or have medical management of their miscarriage.

Miscarriage complications

• Expectant management has been shown to lead to a higher risk of incomplete miscarriage, need for unplanned (or additional) surgical emptying of the uterus, bleeding and need for transfusion.⁹

• Guidelines vary from country to country. In the UK, expectant management is advised initially. In the USA, all three options are offered with equal weighting. ²Some women prefer a more "natural" process whilst others prefer to have a more definitive procedure. Psychological outcomes have been found to be similar with all management options.⁹

• After complete miscarriage, bleeding normally ceases within 10 days. If there is retention of any of the products of conception, bleeding may continue with cramps. If this occurs then surgery is often required.

• The 2017-2019 triennial report from Mothers and Babies: Reducing Risk through Audit and Confidential Enquiries across the UK (MBRRACE-UK) into maternal deaths in the UK and Ireland, highlighted the importance that loss of a child, including by miscarriage, has on a woman's vulnerability to mental illness and that she will need additional monitoring and support.¹⁰

• Mental health impacts are similar across all areas though coping mechanisms differ depending on social beliefs and attitudes,¹¹ but depression, anxiety and perinatal grief are more common in women of lower socio-economic status, who are of low educational achievement and who are Black, or in women who are childless.¹²

Prognosis

• Threatened miscarriage is associated with risk of subsequent preterm delivery.

• After one miscarriage, there is increased risk of further miscarriages. Three consecutive miscarriages lead to a diagnosis of recurrent spontaneous miscarriage which means women are eligible for referral to a specialist centre. Fewer than 5% of women will experience 2 consecutive miscarriages and fewer than 1% will experience three or more.

• The first months after a miscarriage are often accompanied by feelings of grief, guilt, anxiety, and depression for both the patient and her partner, especially in cases of recurrent loss, fertility challenges, loss of a highly desired pregnancy, and in patients with pre-existing mental health concerns.²

• Attempting conception immediately after resolution of early pregnancy loss is safe, and couples who attempt conception within 3 months after miscarriage experience higher rates of successful pregnancy and live birth than those who postpone conception.² Despite this, women often receive the incorrect advice to postpone trying to conceive, following a miscarriage.

Miscarriage prevention

Encourage:

• Reduction/cessation of alcohol consumption.

• Smoking cessation and stopping illicit drug use.

Whilst vitamin supplementation prior to, or in early pregnancy, does not prevent miscarriage, there is evidence that multivitamins with iron and folic acid do reduce the risk of stillbirth.¹³