What are the management strategies for a high-risk multiple pregnancy, particularly in women with a history of multiple pregnancies or fertility treatments?

Identification and Management of Multiple Pregnancies

Multiple pregnancies require intensive ultrasound surveillance with chorionicity determination in the first trimester being the single most critical step, as monochorionic twins carry a 10% mortality rate and require biweekly monitoring starting at 16 weeks, while dichorionic twins need less frequent surveillance every 3-4 weeks. 1

Why Multiple Pregnancies Are High-Risk

Multiple gestations carry substantially elevated mortality and morbidity compared to singletons:

• 5-fold increase in fetal death and 7-fold increase in neonatal death, primarily from complications of prematurity 1
• Preterm delivery risk is proportional to fetal number, with the majority of adverse outcomes stemming from early delivery 1
• Growth restriction occurs more frequently, particularly in the third trimester and especially in monochorionic twins 1
• Congenital anomalies are significantly increased: affecting 1 in 25 dichorionic twins, 1 in 15 monochorionic-diamniotic twins, and 1 in 6 monoamniotic twins 1
• Placental complications are more common, including placenta previa, vasa previa, and velamentous cord insertion 1
• Monochorionic twins face unique life-threatening complications including twin-to-twin transfusion syndrome (TTTS), twin anemia-polycythemia sequence (TAPS), and twin reversed arterial perfusion (TRAP) sequence, with overall mortality around 10% 1

First Trimester Identification and Assessment

Both transabdominal and transvaginal ultrasound should be performed in the first trimester when multiple pregnancy is known or suspected 1:

• Determine chorionicity and amnionicity—this is most accurately done in the first trimester and dictates all subsequent management 1
• Perform pregnancy dating when crown-rump length measures 45-84 mm during nuchal translucency evaluation 1
• Refer to a specialist immediately if crown-rump length discrepancy ≥10% or nuchal translucency discordance ≥20%, as this carries up to 30% risk of severe TTTS or early fetal demise 1

Critical First Trimester Pitfall

Crown-rump length discordance ≥10% predicts pregnancy loss, though with only 52% positive predictive value, so close surveillance rather than immediate intervention is warranted 1.

Second Trimester Management

Routine Anatomic Survey (18-22 weeks)

For dichorionic twins 1:

• Transabdominal ultrasound for fetal anatomy assessment 1
• Transvaginal cervical length assessment to stratify preterm delivery risk 1
• Fetal echocardiography if conceived via in vitro fertilization 1
• Evaluate for vasa previa and velamentous cord insertion, which are more common and associated with adverse outcomes 1

For monochorionic twins 1:

• All of the above, plus:
• Mandatory fetal echocardiography to screen for congenital cardiac disease, which has elevated risk in monochorionic twins 1
• Doppler velocimetry assessment 1
• Begin screening for TTTS 1

Third Trimester Surveillance Protocols

Dichorionic Twins Without Complications 1

• Growth ultrasound every 3-4 weeks starting after the anatomy scan 1, 2
• Calculate and document estimated fetal weight discordance at each scan 1
• If growth discordance or amniotic fluid abnormalities develop, increase surveillance frequency 1

Monochorionic Twins 1, 2

This is where management diverges significantly:

• Begin surveillance at 16 weeks 1
• Fetal biometry every 2-3 weeks 1
• Assessment for TTTS every 2 weeks, evaluating amniotic fluid measurements, bladder visualization, pleural effusions, ascites, and umbilical artery Doppler 1
• Some evidence suggests weekly ultrasound may be superior for early detection of critical complications and preventing unexpected fetal death 1

Defining and Managing Growth Discordance

Growth discordance ≥20-25% is the threshold for concern and intensified surveillance 1:

Selective Fetal Growth Restriction (sFGR) Criteria 1

For any chorionicity:

• One criterion alone: Estimated fetal weight <3rd percentile 1

For monochorionic twins, ≥2 of 4 criteria:

• Estimated fetal weight <10th percentile 1
• Abdominal circumference <10th percentile 1
• Estimated fetal weight discordance ≥25% 1
• Umbilical artery pulsatility index >95th percentile in smaller twin 1

For dichorionic twins, ≥2 of 3 criteria:

• Estimated fetal weight <10th percentile 1
• Estimated fetal weight discordance ≥25% 1
• Umbilical artery pulsatility index >95th percentile in smaller twin 1

Management of Growth Discordance

• Abdominal circumference discordance >10% between 14-22 weeks is the single best predictor of adverse outcome for both chorionicity types 1
• Umbilical artery Doppler is essential when growth delay is suspected and in all monochorionic twins 1
• Absent or reversed end-diastolic flow carries high risk of fetal death in the growth-restricted twin and neurological morbidity in the surviving twin 1
• Nonstress testing and biophysical profile are as reliable in multiples as singletons when standard obstetric indications exist 1

Monochorionic-Specific Complications Requiring Intervention

Twin-to-Twin Transfusion Syndrome (TTTS)

• Surveillance begins at 16 weeks with biweekly assessment 1
• Evaluate amniotic fluid volumes, bladder visualization, cardiac function, and Doppler parameters 1
• Fetal intervention may be required; continue surveillance even post-intervention 1

Twin Reversed Arterial Perfusion (TRAP) Sequence

• Mortality of pump twin is approximately 50% without intervention 1
• Calculate TRAP fetus volume at each scan 1
• Intervene when TRAP fetus weight reaches 50% of pump twin weight or when cardiac decompensation develops in pump twin 1
• Cardiac evaluation of pump fetus is mandatory to assess volume overload 1

Special Considerations for Fertility Treatment Patients

Women with multiple pregnancies from assisted reproductive technology require the same surveillance protocols, but counseling should address:

• The preventable nature of higher-order multiples through embryo transfer limitation 3, 4
• Single embryo transfer combined with frozen embryo transfer effectively reduces multiple birth rates while maintaining acceptable live birth rates 5
• History of fertility treatment does not change ultrasound surveillance protocols but may increase baseline risk of single umbilical artery (4-6 fold increased risk in twins) 6

Critical Management Algorithm Summary

First trimester: Determine chorionicity → If monochorionic, plan intensive surveillance 1

16 weeks onward (monochorionic only): Begin biweekly TTTS screening + biometry every 2-3 weeks 1

18-22 weeks (all multiples): Anatomy scan + cervical length + cardiac echo (if monochorionic or IVF) 1

Third trimester dichorionic: Growth scans every 3-4 weeks 1

Third trimester monochorionic: Continue biweekly surveillance, biometry every 2-3 weeks 1

Any discordance ≥20-25% or complications: Increase surveillance frequency, add Doppler assessment, consider antenatal testing 1