Multiple Gestation Pregnancy
Pregnancy with >=2 fetuses; chorionicity drives risk profile and management.
Also known as: twins, multiple gestation, twin pregnancy, triplet pregnancy, MCDA, DCDA
Overview
Pregnancy carrying two or more fetuses. Classified by zygosity (monozygotic vs dizygotic) and, more clinically importantly, by chorionicity and amnionicity: dichorionic-diamniotic (DCDA), monochorionic-diamniotic (MCDA), or monochorionic-monoamniotic (MCMA).
Epidemiology
Twin rate ~3% of live births (driven up by assisted reproductive technology and advanced maternal age). About two-thirds of spontaneous twins are dizygotic.
Keep reading — start your free trial
You've read your 2 free diagnosis previews. Create your free account to unlock the full Multiple Gestation Pregnancy outline — plus all 514 diagnoses, 5,500+ board-style questions, flashcards, and an AI tutor. Your 7-day free trial includes everything, and there's no credit card required.
Risk factors
- Assisted reproductive technology (especially IVF with multiple embryo transfer, ovulation induction with clomiphene or letrozole or gonadotropins)
- Advanced maternal age (higher FSH levels)
- Family history of dizygotic twins (maternal side)
- African ancestry (higher dizygotic rate); Asian ancestry (lower)
- Higher parity, taller stature
Pathophysiology
Dizygotic twins arise from fertilization of two separate ova by two sperm — always DCDA, separate placentas, genetically siblings. Monozygotic twins arise from a single fertilized egg splitting. Timing of cleavage determines chorionicity: 0-3 days = DCDA; 4-8 days = MCDA (most common monozygotic, ~70%); 8-13 days = MCMA; >13 days = conjoined twins.
Clinical presentation
Symptoms
- Often diagnosed on first-trimester ultrasound
- Exaggerated symptoms of pregnancy (nausea, breast tenderness)
- Earlier and larger fundal height for gestational age
- Earlier perception of fetal movement
Signs / physical exam
- Fundal height greater than expected (>3 cm above expected for GA)
- Auscultation of two distinct fetal heart rates with different rhythms
- Maternal weight gain above expected
Differential diagnosis
- Singleton with hyperestrogenic uterine enlargement / fibroids — Single fetal pole on US; fibroids visualized
- Molar pregnancy — Very high beta-hCG, no fetus, 'snowstorm' US — rare combined molar + viable twin requires expert management
Diagnostic workup
Diagnostic criteria
Ultrasound visualization of multiple gestational sacs/embryos with documentation of chorionicity in the first trimester.
Labs
- Routine prenatal labs as for singleton; CBC follow-up given higher anemia risk
- First-trimester aneuploidy screening with cell-free DNA is more complex in twins (must specify dichorionic vs monochorionic for risk interpretation)
- Glucose tolerance testing (higher GDM rates)
Imaging
- First-trimester ultrasound (6-14 wk) — most accurate time to determine chorionicity and amnionicity
- - 'Twin peak' (lambda) sign = dichorionic
- - 'T sign' (perpendicular dividing membrane joining placenta) = monochorionic-diamniotic
- - No intertwin membrane = monoamniotic
- Serial growth ultrasounds every 4 weeks (dichorionic) or every 2 weeks starting at 16 wk (monochorionic)
- Targeted anatomic survey at 18-22 wk
- Antepartum surveillance (NST/BPP) per chorionicity and complications
Diagnostic algorithm
| Type | Chorionicity/Amnionicity | First-Trimester US Sign | Recommended Delivery |
|---|---|---|---|
| Dichorionic-Diamniotic | 2 placentas, 2 sacs | Lambda / twin peak sign | 38 0/7 - 38 6/7 wk |
| Monochorionic-Diamniotic | 1 placenta, 2 sacs | T sign | 36 0/7 - 37 6/7 wk |
| Monochorionic-Monoamniotic | 1 placenta, 1 sac | No dividing membrane | 32 0/7 - 34 0/7 wk by cesarean |
Treatment
First-line
- Early establishment of chorionicity is essential — drives surveillance plan
- Folic acid 1 mg daily (some recommend higher in multiples)
- Nutritional counseling: greater caloric and weight gain targets per IOM
- Low-dose aspirin 81 mg daily starting 12-28 wk, ideally before 16 wk (USPSTF/ACOG/SMFM — multiple gestation is a HIGH-risk factor for preeclampsia; a single high-risk factor alone warrants aspirin)
- Discourage routine bed rest, prophylactic tocolysis, and prophylactic cerclage — none reduce preterm birth
- Screen for gestational diabetes and anemia; iron supplementation
DCDA — delivery timing
- Recommended delivery 38 0/7 to 38 6/7 wk per ACOG/SMFM if uncomplicated
MCDA — delivery timing and monitoring
- Serial growth and amniotic fluid ultrasounds every 2 weeks from 16 wk to monitor for twin-twin transfusion syndrome (TTTS), selective IUGR, twin anemia-polycythemia sequence (TAPS)
- Recommended delivery 36 0/7 to 37 6/7 wk if uncomplicated
MCMA — delivery timing and monitoring
- Inpatient monitoring usually from 24-28 wk due to cord entanglement risk
- Recommended delivery 32 0/7 to 34 0/7 wk by cesarean
Mode of delivery (DCDA/MCDA)
- Vaginal delivery acceptable when both twins vertex; consider for vertex/non-vertex if experienced operator (breech extraction of second twin)
- Cesarean for non-vertex presenting twin, monoamniotic twins, or conjoined twins
Second-line / adjunct
- Fetoscopic laser photocoagulation for severe TTTS at 16-26 wk (Solomon technique)
- Selective reduction for higher-order multiples (typically triplet to twin) to improve outcomes
Complications
- Preterm birth (>50% of twins, ~90% of triplets)
- Hypertensive disorders of pregnancy (preeclampsia rate doubled), gestational diabetes, anemia
- Polyhydramnios, oligohydramnios, IUGR, discordant growth
- Monochorionic-specific: twin-twin transfusion syndrome (TTTS), TAPS, selective IUGR, twin reversed arterial perfusion (TRAP) sequence, conjoined twins, cord entanglement (MCMA)
- Operative delivery, postpartum hemorrhage, increased NICU admission and neonatal mortality
PANCE pearls
- Chorionicity is most accurately determined in the first trimester — request and document this on any twin ultrasound.
- TTTS (oligohydramnios in donor, polyhydramnios in recipient with intertwin discordance) is treated with fetoscopic laser ablation, NOT amnioreduction alone, when criteria met.
- Monoamniotic twins are at risk of cord entanglement and stillbirth — inpatient monitoring with daily NST is standard from 24-28 wk.
- Vanishing twin: loss of one twin in the first trimester occurs in up to 30% of twins; usually no maternal sequelae.
- Twin B is at higher risk of cord prolapse, abruption, and intrapartum compromise once Twin A delivers.
References
- ACOG/SMFM PB 231 — ACOG/SMFM Practice Bulletin 231: Multifetal Gestations (Obstet Gynecol 2021)
- SMFM #44 — SMFM Consult Series #44: Management of Monochorionic Twin Pregnancies
- Eunice Kennedy Shriver NICHD — Medically Indicated Late-Preterm and Early-Term Deliveries (ACOG/SMFM 2021)
Practice Reproductive questions on FirstPassPA
Turn this outline into retention. 5,500+ board-style questions with an AI tutor that explains every answer — free to start, no card required.
Start studying free → Browse all 514 diagnosesEducational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.