What is the recommended management for a pregnancy with dichorionic diamniotic (two separate placentas and two separate amniotic sacs) twins?

Management of Dichorionic Diamniotic Twin Pregnancies

Dichorionic diamniotic twins require less intensive surveillance than monochorionic twins, with ultrasound monitoring every 3-4 weeks starting at 18-22 weeks and planned delivery at 37-38 weeks of gestation. 1

Initial Assessment and Chorionicity Determination

Establish chorionicity and amnionicity by first trimester ultrasound (ideally 10-13 weeks' gestation), as this is the single most important prognostic factor in twin pregnancies. 1, 2, 3 Dichorionic twins have significantly lower perinatal mortality compared to monochorionic twins (approximately 2-fold difference). 2

• Dizygotic twins nearly always result in dichorionic diamniotic placentation with two separate placental masses and amniotic sacs. 1
• Dating should be performed in the first trimester when crown-rump length is between 45-84 mm. 1
• For IVF pregnancies, use the date of embryo transfer for accurate gestational age determination. 3

Surveillance Protocol

Frequency of Ultrasound Monitoring

Perform ultrasound surveillance every 3-4 weeks starting from the anatomy scan (18-22 weeks) for uncomplicated dichorionic pregnancies. 1, 3, 4 This is less frequent than monochorionic twins, which require every 2-week monitoring. 2, 3

Key Components of Each Ultrasound

• Fetal anatomic survey at 18-22 weeks to screen for anomalies, which occur in approximately 1 in 25 dichorionic twin pregnancies. 1
• Growth assessment using singleton growth curves, as these currently provide the best predictors of adverse outcomes in twins. 3
• Amniotic fluid assessment using deepest vertical pocket (oligohydramnios <2 cm, polyhydramnios >8 cm). 3
• Cervical length measurement via transvaginal ultrasound at the time of anatomic survey to assess preterm birth risk. 1
• Evaluation for vasa previa and velamentous cord insertion, which are more common in multiple gestations. 1

Growth Monitoring and Discordance

Define growth discordance as either ≥20 mm difference in abdominal circumference or ≥20% difference in estimated fetal weight. 3

• Increase surveillance frequency when growth restriction is diagnosed in one twin or significant growth discordance is present. 3
• Selective intrauterine growth restriction (sIUGR) most commonly results from unequal placental sharing. 1
• Consider other causes of growth restriction including viral infection or chromosomal abnormalities. 1

Doppler Assessment

Do not routinely perform umbilical artery Doppler in uncomplicated dichorionic twin pregnancies. 3

• Reserve Doppler studies for complications involving placental circulation or fetal hemodynamic abnormalities. 3
• The role of Doppler in dichorionic twins without growth restriction remains uncertain. 1

Aneuploidy Screening

Offer first trimester combined screening with nuchal translucency measurements, which provides detection rates over 85% in dichorionic twins—close to singleton performance. 1, 3

• Use a threshold of ≥3 mm at 11-14 weeks to define increased nuchal translucency. 1
• Generate individual fetus-specific risks for each twin. 1
• Sample both twins during diagnostic testing even if only one appears at risk, to avoid missed diagnoses. 1
• Perform detailed anatomic survey and fetal echocardiography in the second trimester for twins with increased nuchal translucency or diagnosed aneuploidy. 1

Delivery Timing and Mode

Plan delivery at 37-38 weeks of gestation for uncomplicated dichorionic diamniotic twins. 1, 4

• Administer one course of corticosteroids for fetal lung maturation if preterm delivery is anticipated between 24-33 6/7 weeks. 5
• Mode of delivery should be based on standard obstetric indications and fetal presentation, not chorionicity alone. 1

Important Caveats

• Dichorionic twins account for approximately 70% of all twin pregnancies but carry substantially lower risk than monochorionic twins. 1
• Despite lower risk, dichorionic twins still face a 5-fold increase in fetal death and 7-fold increase in neonatal death compared to singletons, primarily from prematurity complications. 1
• Maternal complications including hypertensive disorders, preterm labor, and placenta previa occur more frequently than in singleton pregnancies. 1, 6
• Consider referral to a specialized twin clinic, as evidence suggests improved obstetrical outcomes with specialized care. 6
• Increase surveillance frequency if complications develop, including cervical shortening, fetal anomalies, growth disturbances, or amniotic fluid abnormalities. 1