A unicornuate uterus is a congenital Müllerian duct anomaly in which only one half of the uterus develops normally. It accounts for approximately 2.5-10% of all Müllerian anomalies and is associated with some of the highest adverse reproductive risks among uterine malformations.
Anatomy
A unicornuate uterus consists of:
• One normally developed uterine horn
• A single fallopian tube on the developed side
• Variable development of a contralateral rudimentary horn
The rudimentary horn may be:
1. Communicating
2. Non-communicating with cavity
3. Non-communicating without cavity
4. Completely absent
The most dangerous situation is a pregnancy in a non-communicating rudimentary horn, which usually ruptures in the 2nd trimester.
Associated anomalies
Renal anomalies occur in approximately 30-40%.
Common associations:
• Unilateral renal agenesis
• Ectopic kidney
• Horseshoe kidney
• Duplicated collecting system
Therefore, whenever a unicornuate uterus is diagnosed, renal imaging is recommended.
Fertility
Many women conceive naturally.
Fertility is reduced because of:
• Reduced uterine volume
• Altered blood supply
• Associated endometriosis
• Tubal abnormalities
Pregnancy Risks
A unicornuate uterus is considered a high-risk obstetric condition.
| Complication | Approximate Risk |
|---|---|
| First-trimester Miscarriage | 20–30% |
| Second-trimester Loss | 10–20% |
| Preterm Birth | 20–45% |
| Fetal Growth Restriction (FGR) | Increased |
| Malpresentation | 30–50% |
| Cesarean Delivery | Increased |
| Cervical Insufficiency | Increased |
| Placental Abnormalities | Increased |
Why adverse outcomes occur
Reduced uterine volume - The fetus grows within a relatively smaller cavity.
Abnormal myometrial architecture - The uterus may not distend normally.
Altered uterine blood flow - Potentially contributes to:
• Growth restriction
• Placental insufficiency
Cervical dysfunction - Can predispose to:
• Cervical shortening
• Mid-trimester loss
• Preterm birth
First Trimester Management
Confirm:
• Viability
• Exact implantation site
• Exclude rudimentary horn pregnancy
This is critical.
Cervical Length Surveillance
Many experts perform serial transvaginal cervical length assessment:
Common schedule: Every 2 weeks from 16-24 weeks
Short cervix: Vaginal progesterone
• Selected cases may require cerclage
Routine prophylactic cerclage for all unicornuate uteri is controversial.
Fetal Growth Surveillance
Because of increased FGR risk:
Growth scans are commonly performed:
• Every 3-4 weeks in the third trimester
Assess:
• Estimated fetal weight
• Dopplers
• Amniotic fluid
Preterm Birth
One of the major concerns.
Mechanisms:
• Limited uterine distensibility
• Cervical insufficiency
• Abnormal placentation
Management:
• Cervical surveillance
• Progesterone when indicated
• Standard preterm birth prevention strategies
Fetal Malpresentation
Very common because of the asymmetric cavity.
Common presentations:
• Breech; Transverse lie; Oblique lie
Hence cesarean rates are high.
Placental Problems
Increased risk of:
• Placenta previa; Placental insufficiency; Retained placenta
• Placenta accreta spectrum
Mode of Delivery
A unicornuate uterus alone is not an indication for cesarean section.
Vaginal delivery can be attempted if:
• Cephalic presentation
• No obstetric contraindication
• Reassuring fetal status
However, cesarean rates are substantially higher due to:
• Breech presentation
• Fetal distress
• Labor abnormalities
Does fetal reduction improve outcomes?
Generally:
• A singleton pregnancy in a unicornuate uterus performs better than a twin pregnancy in a unicornuate uterus.
• Reduction decreases uterine distension and may reduce the risk of very early preterm delivery.
Counseling
For a woman with a unicornuate uterus carrying twins:
• Continuing twins is possible, and successful outcomes are reported.
• The pregnancy is at very high risk for preterm birth.
• Selective reduction to a singleton may improve the likelihood of a longer gestation and higher birth weight.