Types of Miscarriages
Early pregnancy loss (EPL) is the preferred term for describing a pregnancy that may not progress, is in the process of expulsion, or has incompletely or completely passed; this terminology replaces older terms like "pregnancy failure" or "blighted ovum." 1
Classification of Miscarriages
Based on Clinical Presentation
Threatened Miscarriage: Characterized by vaginal bleeding with or without abdominal cramps in a viable pregnancy. Occurs in approximately 20% of recognized pregnancies 2
Incomplete Miscarriage: Defined as the presence of intracavitary tissue, typically with internal vascularity, or a persistent gestational sac following pregnancy loss 1
Complete Miscarriage: No persistent gestational sac or intracavitary tissue following pregnancy loss 1
EPL in Progress: Describes a situation where the gestational sac is located in the lower uterine segment or endocervical canal and is in the process of expulsion 1
Missed Miscarriage: Also termed "silent miscarriage," occurs when the embryo has died but has not been expelled from the uterus. This corresponds to "diagnostic of EPL" in current terminology 1, 3
Based on Ultrasound Findings
Concerning for EPL: Embryonic crown-rump length (CRL) <7 mm with no cardiac activity, mean sac diameter (MSD) 16-24 mm with no embryo, or absence of embryo 7-13 days after visualization of gestational sac 3
Diagnostic of EPL: CRL ≥7 mm with no cardiac activity, MSD ≥25 mm with no embryo, or absence of embryo ≥14 days after visualization of gestational sac 1, 3
Anembryonic Pregnancy: A specific term for a gestational sac measuring 25 mm or larger without an embryo, or absence of an embryo on serial examinations obtained at discriminatory time intervals 1
Embryonic Demise: Refers to a specific scenario when the crown-rump length is 7 mm or longer and there is absence of cardiac activity 1
Based on Frequency
Sporadic Miscarriage: The most common type, representing a single pregnancy loss 4
Recurrent Miscarriage: Defined as two or three consecutive pregnancy losses, considered a distinct disease entity with multiple potential etiologies 4, 5
Special Types
Pregnancy of Unknown Location (PUL): A transient state referring to patients with a positive pregnancy test and no evidence of an ectopic pregnancy or an intrauterine pregnancy on transvaginal ultrasound 1
Gestational Trophoblastic Disease: A rare condition where abnormal trophoblastic tissue grows in the uterus, including hydatidiform moles (complete or partial) 1
Epidemiology and Risk Factors
The pooled risk of miscarriage is 15.3% of all recognized pregnancies, with an estimated 23 million miscarriages occurring worldwide annually 6
Population prevalence: 10.8% of women have experienced one miscarriage, 1.9% have had two miscarriages, and 0.7% have had three or more miscarriages 6
Risk factors include maternal age (younger than 20 or older than 35 years), paternal age over 40 years, extremes of BMI, Black ethnicity, previous miscarriages, smoking, alcohol consumption, stress, night shift work, air pollution, and pesticide exposure 6
Poor prognostic indicators include a calcified yolk sac and an enlarged amniotic cavity relative to the crown-rump length (expanded amnion sign) 1
Consequences of Miscarriage
Physical consequences: Bleeding, infection, and increased risk for obstetric complications in future pregnancies (preterm birth, fetal growth restriction, placental abruption, and stillbirth) 6
Psychological consequences: Increased risk of anxiety, depression, post-traumatic stress disorder, and suicide 6
Long-term health implications: Predictor of longer-term health problems such as cardiovascular disease and venous thromboembolism 6
Management Considerations
Management options for incomplete miscarriage include expectant management, medical management with misoprostol, or surgical evacuation (suction dilation and curettage) 3
Surgical evacuation is preferably performed under ultrasound guidance to reduce the risk of uterine perforation 3
Threatened miscarriage is associated with increased risk of preterm birth (OR: 1.95), low birth weight (OR: 2.33), and subsequent abortion (OR: 2.55) 7
Serial hCG monitoring is recommended until levels return to the non-pregnant state 3
Histopathologic examination of tissue is recommended to confirm intrauterine pregnancy and rule out gestational trophoblastic disease 3
Prevention and Future Considerations
For women with recurrent miscarriage, specialized care in preconception and high-risk obstetric clinics is recommended 6
Recent research suggests that the decidualized endometrium may act as a biosensor of embryo quality, which if disrupted, may lead to implantation of embryos destined to miscarry 4
New insights into mechanisms behind miscarriage offer the prospect of novel interventions that may prevent this distressing condition 4