What are the causes of a 2nd trimester miscarriage?

Causes of 2nd Trimester Miscarriage

The most common causes of second trimester miscarriage include cervical insufficiency, placental abnormalities, antiphospholipid syndrome, uterine anomalies, and preterm premature rupture of membranes, with cervical insufficiency having the highest recurrence rate at approximately 28% when untreated. 1, 2

Major Causes of Second Trimester Miscarriage

Structural/Anatomical Causes

• Cervical insufficiency: Painless cervical dilation leading to pregnancy loss, with the highest recurrence rate (28%) among all causes 2
• Uterine anomalies: Congenital malformations of the uterus that can compromise pregnancy maintenance 1
• Multiple gestations: Twin-to-twin transfusion syndrome (TTTS) affects 10-20% of monochorionic twins, with severe cases evident before 20 weeks carrying mortality rates exceeding 70% 3

Placental/Vascular Causes

• Placental abruption: Premature separation of the placenta, affecting approximately 1% of pregnancies 3
• Placenta previa: Abnormal placental implantation over the cervical os, occurring in about 1 in 200 pregnancies 3
• Vasa previa: Fetal vessels crossing the cervical os, occurring in 1 in 2,500 to 1 in 5,000 deliveries 3
• Antiphospholipid syndrome: Found in 18.3% of second trimester miscarriage cases 1

Fetal Causes

• Fetal anomalies: Structural or chromosomal abnormalities incompatible with continued development 4
• Intrauterine fetal death: Accounts for 64.6% of second trimester losses 5

Membrane-Related Causes

• Preterm premature rupture of membranes (PPROM): Accounts for 17.7% of second trimester losses 5
• Preterm labor: Accounts for 17.7% of second trimester losses 5

Maternal Medical Conditions

• Thrombophilias: Blood clotting disorders that can cause placental thrombosis and infarction 6
• Diabetes mellitus: Can contribute to pregnancy complications and second trimester loss 4
• Infections: May lead to chorioamnionitis and subsequent pregnancy loss

Diagnostic Approach

When evaluating second trimester miscarriage, investigations should be guided by the clinical presentation, which can be categorized into three phenotypes:

1. Silent miscarriage (ST-SM): Fetal demise without membrane rupture
2. Rupture of membranes (ST-ROM): Premature rupture of membranes
3. Inevitable miscarriage (ST-IM): Active miscarriage with cervical dilation 4

Essential Investigations

• Transvaginal ultrasound: Primary diagnostic tool to assess pregnancy viability 3
• Placental histology: More likely to yield significant results in cases of ST-ROM and ST-SM 4
• Karyotype examination: Important for identifying chromosomal abnormalities 4
• Thrombophilia screening: Particularly for antiphospholipid syndrome, which accounts for 67% of procoagulant defects in recurrent miscarriage 6

Recurrence Risk and Prevention

The overall recurrence rate for second trimester miscarriage is approximately 7.3%, but varies significantly by cause:

• Cervical insufficiency: 28% without intervention
• Other causes (fetal anomaly, multiple gestations, intrauterine fetal death): <5% 2

Prevention Strategies

• Cervical cerclage: For cervical insufficiency, vaginal cerclage reduces recurrence (adjusted OR 0.47), while abdominal cerclage provides even greater reduction (adjusted OR 0.14) 2
• Anticoagulation therapy: For antiphospholipid syndrome and other thrombophilias, preconception aspirin (81mg/day) plus postconception heparin can result in >98% successful term deliveries 6
• Cervical length monitoring: Recommended for women with history of ST-ROM and ST-IM 4

Clinical Pitfalls and Considerations

• Despite comprehensive investigation, the cause of second trimester miscarriage remains unidentified in approximately 57.5% of cases 1
• Women with PPROM have significantly higher odds of requiring antibiotic therapy (OR 13.75) and hospital readmission (OR 4.15) compared to those with intrauterine fetal demise 5
• Second trimester miscarriage represents a distinct cohort with high rates of morbidity requiring medical intervention 5
• Future pregnancy outcomes are generally reassuring, with approximately 60.9% of women having a live birth in subsequent pregnancies 1

Understanding the specific cause of second trimester miscarriage is crucial for counseling and management of subsequent pregnancies, as interventions can significantly improve outcomes, particularly in cases of cervical insufficiency.