Definition and epidemiology
Abortion is the termination of pregnancy before the fetus reaches viability (generally defined as before 20-24 weeks gestation, depending on jurisdiction). It is classified broadly into two categories:
- Spontaneous abortion (miscarriage): unintended pregnancy loss, occurring in an estimated 10-15% of clinically recognized pregnancies, with higher rates when including biochemical pregnancies that are never clinically recognized.
- Induced abortion: intentional termination of pregnancy using medical (pharmacologic) or surgical methods, performed for elective, medical, or genetic reasons.
Spontaneous abortion risk rises sharply with maternal age, from roughly 10% in women under 30 to over 50% in women over 45. Induced abortion is one of the most common gynecologic procedures globally, with rates varying widely by country based on legal access, contraceptive use, and socioeconomic factors.
ICD-10 code O04 specifically refers to medical abortion (termination of pregnancy performed with medical/surgical assistance), distinct from codes used for spontaneous abortion (O03) or missed abortion (O02.1).
- Chromosomal abnormalities (mostly trisomies) cause the majority of first-trimester spontaneous abortions.
- Always rule out ectopic pregnancy first in any early pregnancy bleeding.
- Threatened abortion = bleeding with a closed cervix and a viable pregnancy on ultrasound.
- Rh-negative patients need Rh immunoglobulin after any pregnancy loss or abortion.
- Mifepristone (progesterone antagonist) plus misoprostol (prostaglandin analog) is standard first-line medical regimen.
- A beta-hCG that fails to double appropriately in 48 hours suggests a nonviable pregnancy.
- Recurrent pregnancy loss (2+ losses per ASRM/ACOG) triggers workup for antiphospholipid syndrome, uterine anomalies, and genetic causes.
- Septic abortion presents with fever, foul-smelling discharge, and uterine tenderness and requires antibiotics plus evacuation.
Etiology and risk factors
Spontaneous abortion
- Chromosomal abnormalities (50-60% of first-trimester losses), most commonly autosomal trisomies, followed by monosomy X and triploidy
- Advanced maternal age (strongest independent risk factor)
- Uterine structural abnormalities (septate uterus, fibroids, Asherman syndrome)
- Antiphospholipid syndrome and other thrombophilias (recurrent loss)
- Endocrine disorders: poorly controlled diabetes, thyroid dysfunction, luteal phase defect
- Infections: TORCH organisms, bacterial vaginosis
- Lifestyle factors: smoking, heavy alcohol use, cocaine use
- Prior history of miscarriage (risk increases with each successive loss)
Induced abortion
- Elective termination for unintended or unwanted pregnancy
- Maternal medical indications (severe cardiac, renal, or oncologic disease incompatible with pregnancy continuation)
- Fetal indications (lethal or severe chromosomal/structural anomalies detected on prenatal screening)
- Pregnancy resulting from rape or incest
- Psychosocial factors (financial, relationship, educational circumstances)
Pathophysiology
Spontaneous abortion most often begins with failure of normal embryonic/fetal development, frequently due to chromosomal nondisjunction during gametogenesis. This leads to abnormal placentation and inadequate trophoblastic invasion, triggering decidual breakdown, bleeding, and eventual expulsion of products of conception. Later losses (after 10 weeks) are more likely attributable to maternal factors such as uterine anomalies, cervical insufficiency, or autoimmune disease rather than genetic defects.
Induced medical abortion relies on pharmacologic disruption of pregnancy maintenance:
- Mifepristone is a progesterone receptor antagonist that causes decidual breakdown, cervical softening, and increased myometrial sensitivity to prostaglandins.
- Misoprostol, a prostaglandin E1 analog, induces myometrial contractions and cervical dilation, leading to expulsion of the products of conception.
Surgical abortion (vacuum aspiration or dilation and evacuation) mechanically removes the products of conception, with gestational age determining the specific technique required.
Clinical features
Spontaneous abortion
- Vaginal bleeding (ranging from light spotting to heavy bleeding)
- Lower abdominal or pelvic cramping
- Passage of tissue or clots
- Resolution of pregnancy symptoms (nausea, breast tenderness) in some cases
- Cervical os may be open (inevitable/incomplete abortion) or closed (threatened abortion)
Classification of spontaneous abortion
| Type | Features |
|---|---|
| Threatened | Bleeding, closed cervix, viable pregnancy on ultrasound |
| Inevitable | Bleeding, open cervix, no tissue passed yet |
| Incomplete | Partial passage of products of conception, open cervix |
| Complete | Full expulsion, closed cervix, empty uterus on ultrasound |
| Missed | Fetal demise without expulsion, closed cervix, often asymptomatic |
| Septic | Infected retained tissue, fever, foul discharge, uterine tenderness |
Induced abortion
Clinical presentation depends on method; patients undergoing medical abortion experience expected cramping and bleeding as the intended therapeutic effect. Post-procedure follow-up assesses for completion and complications.
Diagnosis
Spontaneous abortion
- Transvaginal ultrasound: absence of cardiac activity in an embryo with crown-rump length greater than 7 mm, or empty gestational sac greater than 25 mm mean diameter, confirms nonviability
- Serial beta-hCG: a rising level that fails to double appropriately over 48 hours suggests a failing pregnancy (though this is not diagnostic alone)
- Pelvic examination: assess cervical os status and amount of bleeding
- Complete blood count and blood type/Rh status: assess for anemia and need for Rh immunoglobulin if Rh-negative
Pre-induced-abortion workup
- Confirm gestational age via last menstrual period and/or ultrasound
- Screen for ectopic pregnancy (critical, as symptoms can overlap)
- Assess hemoglobin, blood type and Rh status
- Counseling regarding method options, risks, and alternatives (adoption, parenting) per informed consent requirements
Differential diagnosis
- Ectopic pregnancy — must always be excluded in early pregnancy bleeding; presents with pain, bleeding, and a non-rising or plateauing beta-hCG with no intrauterine pregnancy on ultrasound
- Molar pregnancy (hydatidiform mole) — markedly elevated beta-hCG, "snowstorm" pattern on ultrasound
- Subchorionic hemorrhage — bleeding with a viable intrauterine pregnancy
- Cervical or vaginal pathology (polyps, cervicitis, trauma) causing bleeding unrelated to pregnancy status
- Implantation bleeding — light bleeding in very early pregnancy with no cramping or tissue passage
Management
Spontaneous abortion
Management depends on clinical stability, gestational age, and patient preference, and generally follows three approaches:
- Expectant management: watchful waiting for spontaneous completion, appropriate for stable patients with incomplete or missed abortion
- Medical management: misoprostol (often combined with mifepristone where available) to induce completion
- Surgical management: vacuum aspiration or dilation and curettage, indicated for heavy bleeding, infection, hemodynamic instability, or patient preference
Rh-negative patients require Rh immunoglobulin administration to prevent alloimmunization. Septic abortion requires broad-spectrum antibiotics and prompt uterine evacuation.
Induced abortion
Major guideline bodies (WHO, ACOG, RCOG) support both medical and surgical methods as safe and effective; choice depends on gestational age, patient preference, and local availability.
- Medical abortion: combination of mifepristone followed by misoprostol is first-line up to 10-12 weeks in most protocols (WHO guidance extends medical regimens further with modification); effective in over 95% of cases
- Surgical abortion: vacuum aspiration for first-trimester pregnancies; dilation and evacuation for second-trimester pregnancies
- Pain control, counseling, and contraceptive planning should accompany all procedures
- Follow-up confirms completion via ultrasound or beta-hCG trend
Guideline consensus (WHO, ACOG) emphasizes that abortion is a safe procedure when performed by trained providers, with major complications occurring in well under 1% of cases.
Complications and prognosis
Complications
- Retained products of conception requiring further intervention
- Infection/endometritis, rarely progressing to septic abortion
- Hemorrhage requiring transfusion in rare cases
- Uterine perforation or cervical injury (surgical procedures, rare)
- Asherman syndrome (intrauterine adhesions) following repeated instrumentation
- Rh alloimmunization if immunoglobulin is not administered when indicated
Prognosis
Most women who experience a single spontaneous abortion go on to have successful future pregnancies, as isolated miscarriage does not significantly affect fertility. Recurrent pregnancy loss (defined by ASRM/ACOG as two or more clinical pregnancy losses, with evaluation generally initiated after the second loss) warrants evaluation for underlying anatomic, endocrine, genetic, or autoimmune causes. Induced abortion performed by trained providers using recommended methods carries a low complication rate and does not impair future fertility.
"SAFE" for spontaneous abortion types by cervical os status: Shut (threatened, missed, complete) vs open (inevitable, incomplete) — remember "complete and closed, incomplete and open."
Practice questions
1. A 32-year-old woman at 8 weeks gestation presents with mild vaginal spotting and no cramping. Pelvic examination reveals a closed cervical os. Transvaginal ultrasound shows an intrauterine gestational sac with a fetal pole and cardiac activity appropriate for gestational age. Which of the following is the most likely diagnosis?
2. A 27-year-old woman at 9 weeks gestation undergoes medical termination of pregnancy with mifepristone followed by misoprostol 48 hours later. Which of the following best describes the mechanism of mifepristone in this regimen?
3. A 35-year-old woman with two prior first-trimester pregnancy losses presents for evaluation. Her workup should most appropriately include testing for which of the following conditions as a known cause of recurrent pregnancy loss?
Frequently asked questions
What causes a spontaneous abortion (miscarriage)?
The most common cause is a chromosomal abnormality in the embryo, usually an autosomal trisomy, which prevents normal development. Other contributing factors include advanced maternal age, uterine structural abnormalities, autoimmune conditions like antiphospholipid syndrome, uncontrolled diabetes or thyroid disease, infections, and lifestyle factors such as smoking or heavy alcohol use. Later losses are more often due to maternal anatomic or autoimmune causes than genetic ones.
What are the first signs of a miscarriage?
The earliest signs are usually vaginal bleeding or spotting and lower abdominal cramping. Bleeding can range from light spotting to heavy flow, and cramping may feel similar to or stronger than menstrual cramps. Some women also notice a decrease in pregnancy symptoms like nausea or breast tenderness before other signs appear.
How is a miscarriage or abortion diagnosed?
Diagnosis relies mainly on transvaginal ultrasound to check for fetal cardiac activity and appropriate growth, combined with serial beta-hCG blood tests when ultrasound findings are inconclusive. A pelvic exam helps determine whether the cervix is open or closed, which guides classification and management. Blood type and Rh status are also checked to determine if Rh immunoglobulin is needed.
Is a miscarriage preventable or treatable afterward?
Most isolated miscarriages are not preventable because they result from random chromosomal errors, and treatment focuses on managing the current pregnancy loss safely rather than reversing it. Options include expectant waiting, medication to complete the process, or a minor surgical procedure. After one miscarriage, future pregnancy outcomes are usually good, but recurrent losses (two or more) warrant medical evaluation for an underlying cause.
What is the difference between spontaneous abortion and induced abortion?
Spontaneous abortion, or miscarriage, is an unintended pregnancy loss that happens naturally, most often due to chromosomal abnormalities. Induced abortion is the intentional termination of a pregnancy using medical drugs (mifepristone and misoprostol) or a surgical procedure, performed for elective, medical, or fetal reasons. Both can be managed with similar medical or surgical techniques, but the underlying intent and cause differ.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: O04
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.