What are the statistical complications and recommended management for a pregnant woman carrying dichorionic-diamniotic (di-di) twins?

Statistical Complications of Dichorionic-Diamniotic (Di-Di) Twins

Dichorionic-diamniotic twins carry a 5-fold increased risk of fetal death and 7-fold increased risk of neonatal death compared to singleton pregnancies, primarily due to complications of prematurity. 1

Mortality and Major Outcomes

• Overall perinatal mortality: Dichorionic twins have approximately 2-fold lower mortality compared to monochorionic twins, but remain at substantially elevated risk versus singletons 2
• Fetal/neonatal death: The 5-7 fold increase in mortality is predominantly driven by preterm birth complications 1, 2
• Stillbirth and intrauterine fetal death: Occurs in approximately 3.0% of non-reduced dichorionic twin pregnancies 3

Maternal Complications

Maternal morbidity is significantly elevated across all phases of pregnancy:

• Hypertensive disorders: Increased frequency compared to singleton pregnancies, including preeclampsia 1, 4
• Antepartum hospitalization: Higher rates for preterm labor and abnormal bleeding 4
• Cesarean delivery: Substantially increased rates 4
• Postpartum hemorrhage: More common than in singleton pregnancies 4
• Nutritional deficiencies: Increased risk due to exaggerated physiological demands 4

Fetal and Neonatal Complications

Prematurity-Related Issues

• Preterm delivery before 28 weeks: Occurs in 1.9% of dichorionic twins 3
• Preterm delivery before 32 weeks: Occurs in 7.3% of dichorionic twins 3
• Low birth weight: Significantly increased frequency 5

Structural and Growth Abnormalities

• Congenital anomalies: Approximately 1 in 25 (4%) dichorionic twin pregnancies affected 2
• Selective intrauterine growth restriction (sIUGR): Most commonly results from unequal placental sharing 2
• Growth discordance: Requires close monitoring when significant differences in fetal size or amniotic fluid develop 1

Placental and Cord Complications

• Placenta previa: Higher frequency than singleton pregnancies 1
• Vasa previa: Increased risk, particularly with velamentous cord insertion 1, 2
• Velamentous cord insertion: More common in twin pregnancies, associated with increased risk of small for gestational age, lower gestational age at birth, and intrauterine fetal death 1

Recommended Surveillance Protocol

Initial Assessment

• Chorionicity determination: Must be established by first trimester ultrasound (ideally 10-13 weeks), as this is the single most important prognostic factor 2
• Dating: Should be performed in first trimester when crown-rump length is 45-84 mm 2

Ongoing Monitoring

• Ultrasound frequency: Every 3-4 weeks starting from anatomy scan (18-22 weeks) for uncomplicated dichorionic pregnancies 1, 2
• Anatomic survey: Perform at 18-22 weeks to screen for anomalies 2
• Cervical length: Measure via transvaginal ultrasound at anatomy scan to assess preterm birth risk 2, 5
• Growth assessment: Fetal biometry, amniotic fluid volume, and estimated fetal weight discordance should be calculated and documented at each scan from 20 weeks onward 1
• Doppler assessment: Umbilical artery Doppler after 20 weeks for both twins, though role in dichorionic twins without growth restriction remains uncertain 1, 2

Aneuploidy Screening

• First trimester combined screening: Offers detection rates over 85% in dichorionic twins with nuchal translucency measurements 2
• Nuchal translucency threshold: ≥3 mm at 11-14 weeks defines increased risk 2, 5
• Individual risk assessment: Generate fetus-specific risks for each twin 2
• Diagnostic testing: Sample both twins even if only one appears at risk to avoid missed diagnoses 2

Delivery Timing

Plan delivery at 37-38 weeks of gestation for uncomplicated dichorionic-diamniotic twins. 2, 5

• Corticosteroids: Administer one course for fetal lung maturation if preterm delivery anticipated between 24-33 6/7 weeks 2
• Mode of delivery: Based on standard obstetric indications and fetal presentation, not chorionicity alone 2
• Risk after 32 weeks: Fetal demise risk is low after 32 weeks even in twin pregnancies 1

Critical Caveats

• Dichorionic twins account for approximately 70% of all twin pregnancies but still carry substantially higher risk than singletons despite being lower risk than monochorionic twins 2
• Increase surveillance frequency if complications develop including cervical shortening, fetal anomalies, growth disturbances, or amniotic fluid abnormalities 2
• Specialized twin clinic care has been shown to improve obstetrical outcomes 6
• Early first antenatal visit is critical for correctly identifying number of fetuses and placentation type 6