Miscarriage

Definition/diagnostic criteria
Miscarriage, also known as spontaneous abortion, is defined as the spontaneous loss of a pregnancy before 24 weeks of gestation, with most occurring in the first trimester (before 12 weeks). Miscarriages can be classified into complete, incomplete, missed, and threatened. A complete miscarriage involves the full expulsion of the pregnancy tissue, while an incomplete miscarriage occurs when some tissue remains in the uterus. A missed miscarriage is characterised by an embryo or fetus that has died, but there is no expulsion of tissue, and a threatened miscarriage involves bleeding in early pregnancy with a closed cervix and a viable fetus.

Epidemiology
Miscarriage is a common occurrence, with estimates suggesting that 10-20% of confirmed pregnancies end in miscarriage, though the rate may be higher when considering early, unrecognised losses. The risk increases with maternal age: women under 30 have a miscarriage rate of approximately 10%, while women over 40 face rates of up to 50%. Other risk factors include previous miscarriage, obesity, smoking, excessive alcohol consumption, poorly controlled diabetes, and uterine abnormalities.

Diagnosis

Clinical features
The most common presenting symptom of miscarriage is vaginal bleeding, which may vary from light spotting to heavy bleeding with clots. Cramping or lower abdominal pain often accompanies the bleeding. In some cases, especially with a missed miscarriage, there may be an absence of symptoms, and the diagnosis is made incidentally during a routine ultrasound scan. Pregnancy symptoms such as nausea or breast tenderness may persist for some time after fetal demise.

Investigations
Diagnosis is confirmed via transvaginal ultrasound. In a viable pregnancy, a fetal heartbeat should be visible by 6-7 weeks gestation. Absence of a fetal heartbeat, especially if accompanied by an empty gestational sac (blighted ovum) or abnormal gestational sac size, suggests miscarriage.

Beta-human chorionic gonadotropin (β-hCG) levels may also be measured, although serial measurements are more useful in diagnosing ectopic pregnancy or early pregnancy failure. Falling or plateauing β-hCG levels in early pregnancy indicate a non-viable pregnancy.

Treatment

Threatened miscarriage
If a woman with a history of previous miscarriage has a scan-confirmed intra-uterine pregnancy, offer vaginal micronised progesterone until 16 weeks gestation.

Expectant management
Expectant management involves waiting for the miscarriage to resolve naturally. It is appropriate for women with a confirmed non-viable pregnancy and who are clinically stable, with no signs of infection or heavy bleeding. Studies show that 80% of women will pass pregnancy tissue spontaneously within 2-6 weeks.

Medical management
Medical management uses misoprostol and/or mifepristone, to induce uterine contractions and expel pregnancy tissue. This option may be preferable for women who wish to avoid surgery but do not want to wait for expectant management to complete. Misoprostol is effective in 70-90% of cases. A follow-up scan is typically recommended to ensure complete expulsion.

Surgical management
Surgical options include manual vacuum aspiration (MVA) or dilatation and curettage (D&C). Surgical management is usually indicated when medical or expectant management fails, or if there is heavy bleeding, signs of infection, or patient preference. MVA, which can be done under local anaesthesia, is the preferred method over D&C, as it is quicker and has a lower risk of complications such as uterine perforation.

Prognosis
For most women, the prognosis after miscarriage is excellent, and the majority will go on to have a successful pregnancy in the future. The risk of recurrence after one miscarriage is approximately 20%, but this increases with the number of previous miscarriages. Recurrent miscarriage, defined as three or more consecutive miscarriages, warrants further investigation to identify potential causes such as genetic, anatomic, or autoimmune factors. Psychological support should be offered to all women, as miscarriage can have a significant emotional impact.