Rare and Insightful Case: Triplet Pregnancy with Two Viable Fetuses and One Collapsed Gestational Sac

 Rare and Insightful Case: Triplet Pregnancy with Two Viable Fetuses and One Collapsed Gestational Sac

Triplet pregnancies are uncommon, accounting for only about 1 in every 8,000 naturally conceived pregnancies. With the advent of fertility treatments, however, their frequency has increased. Among the rarer scenarios is a case of triplet gestation where two embryos are viable while the third gestational sac is collapsed and anembryonic. This article presents a clinical overview of such a case, the ultrasound findings, probable causes, and the implications for maternal and fetal outcomes.

🩺 Clinical Background

• The patient was a woman of reproductive age who had undergone ovulation induction therapy, combining oral ovulation stimulants and injectable gonadotropins. She presented for a routine early pregnancy scan at 8 weeks and 6 days gestation, confirmed by her last menstrual period and ovulation tracking.
• She had no previous history of multiple gestations but had been receiving treatment for subfertility for several months.

📊 Ultrasound Findings

Transabdominal and transvaginal ultrasounds revealed:

• Three separate gestational sacs, suggesting a trichorionic triamniotic triplet pregnancy (the least risky form of triplet gestation).
• Two sacs demonstrated clearly visible fetal poles, positive fetal cardiac activity, and active body movements.
• The Crown-Rump Length (CRL) of both viable fetuses was 5.1 cm, which corresponds well with 8 weeks and 6 days of gestation.

However, the third gestational sac appeared collapsed, showing:

• No embryonic pole

• No yolk sac

• Irregular sac shape and reduced volume
• This strongly suggested a case of anembryonic gestation, commonly referred to as a blighted ovum.

🧬 Understanding Anembryonic Pregnancy

• An anembryonic pregnancy occurs when:
• A gestational sac develops, but the embryo either never forms or is reabsorbed very early.It is usually due to chromosomal abnormalities, poor implantation, or inadequate embryonic development.
• Though common in singleton pregnancies, its presence in one sac of a triplet pregnancy is rare and medically significant.

📌 Diagnosis Summary

Final diagnosis:

Trichorionic Triamniotic Triplet Pregnancy

➤ Two viable fetuses with normal growth and development

➤ One collapsed, anembryonic gestational sac

📋 Management Approach

• Management depends on the viability of the fetuses and maternal well-being. In this case

✅ Expectant Management

• The anembryonic sac typically undergoes natural resorption.

• This phenomenon is termed "vanishing twin syndrome" when one fetus in a multiple pregnancy fails to develop and is absorbed.

📅 Follow-Up Plan

• Serial ultrasounds every 2–3 weeks to monitor:
• Growth of viable fetuses
• Placental location
• Any sign of complications (bleeding, restricted growth)

Routine antenatal care for a twin pregnancy

🔍 Prognosis

• The prognosis is favorable for the two viable fetuses. Most patients with similar presentations:
• Continue with an uncomplicated twin pregnancy
• Deliver healthy infants at term or near-term
• Require no intervention for the collapsed sac

However, the patient must be informed about:

• Risks of preterm labor, twin-to-twin transfusion syndrome (if monochorionic), and maternal complications
• The need for nutritional support, close fetal surveillance, and counseling

🧠 Clinical Insight: Why This Case Matters

• This case is insightful because:
• It demonstrates how early ultrasound can identify complex pregnancy types.
• It reflects the importance of differentiating viable and non-viable sacs in multi-fetal pregnancies.
• It emphasizes non-invasive, conservative management in select cases.

As the number of medically assisted conceptions increases, such unusual pregnancy combinations may become more common, necessitating awareness and skilled imaging interpretation.

📚 Conclusion

A triplet pregnancy with two healthy fetuses and one collapsed gestational sac is a rare but important finding. Accurate diagnosis via ultrasound allows clinicians to provide targeted monitoring and improve outcomes. In this case, careful observation and regular prenatal care are key to supporting a healthy twin gestation while allowing the non-viable sac to resolve naturally.