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OG10.1-2,OG11.1 | Late Pregnancy Complications — PBL Case

CLINICAL SETTING

Mrs Anitha, a 27-year-old G1P0, is referred to your antenatal clinic at 14 weeks of gestation from a peripheral health centre. She had a positive urine pregnancy test 10 weeks ago and has had no antenatal visits since. She conceived spontaneously. An obstetric ultrasound performed at the referral centre reported 'twin pregnancy with a single placenta' — no further details were documented. She has no chronic medical conditions, takes no regular medications, and has no family history of twins on her maternal side. On examination she appears well; her uterus is palpable 2 cm above the umbilicus. You arrange an urgent first-level assessment USS which confirms twin pregnancy. The USS report states: 'Twin A: vertex, BPD/FL consistent with 14+2 weeks. Twin B: vertex, BPD/FL consistent with 14+1 weeks. Placenta: single, anterior, appears fused. Dividing membrane: present, thin, inserts into placenta as a T-shaped junction. No gross structural anomalies in either twin.' Liquor appears equal in both sacs.

Trigger 1: Understanding Chorionicity and Its Implications

The USS finding of a thin dividing membrane with a T-sign insertion is shared with the group. You explain that the chorionicity determination at 14 weeks carries major clinical implications for the entire pregnancy.

DISCUSSION POINTS

  • Based on the USS report, what is the chorionicity and amnionicity of this twin pregnancy? What specific USS feature determined this, and why is it more reliably assessed before 16 weeks?
  • Explain the embryological basis of this type of twin pregnancy — when did the zygote split, and why does the timing of splitting determine both chorionicity and amnionicity?
  • What additional risks does this specific type of placentation carry compared with dichorionic diamniotic twins? Name at least three complications unique to or more common in this placentation type.
  • What surveillance plan would you establish for this patient? How frequently would you perform USS, and what specific parameters would you assess at each visit?
Click to reveal Trigger 2: A Concerning Ultrasound at 20 Weeks (discuss previous trigger first!)

Trigger 2: A Concerning Ultrasound at 20 Weeks

At 20 weeks, the scheduled surveillance USS shows: Twin A (donor): deepest vertical pool (DVP) of amniotic fluid = 1.5 cm (oligohydramnios), bladder not visualised despite 30 minutes of scanning. Twin B (recipient): DVP = 10 cm (polyhydramnios), distended bladder, EFW at 75th centile. Twin A EFW at 20th centile. Umbilical artery Doppler in twin A: end-diastolic flow present but reduced. Umbilical artery Doppler in twin B: normal. The patient has no symptoms and fetal movements are normal.

DISCUSSION POINTS

  • What complication has developed? Use the Quintero staging system to classify the severity. State the stage and identify which feature of the USS places it in this stage and not a higher or lower stage.
  • Explain the underlying haemodynamic mechanism through which intraplacental vascular communications lead to this complication — why is one twin a donor and the other a recipient?
  • What are the treatment options available at this stage? Briefly compare the principles behind each option and which is now preferred in a tertiary centre.
  • The family asks: 'Could one of the babies die even if we treat this?' How would you counsel them about the natural history of this condition without treatment and the expected outcomes with the current standard of care?
Click to reveal Trigger 3: Survival of One Twin and a New Crisis at 28 Weeks (discuss previous trigger first!)

Trigger 3: Survival of One Twin and a New Crisis at 28 Weeks

Fetoscopic laser photocoagulation of the placental anastomoses was performed at a tertiary centre at 21 weeks. Both twins survived the procedure. At 24 weeks, twin A showed improved growth velocity; twin B continued to grow normally. However, at 28 weeks, the surveillance USS shows twin A is now growing well (EFW at 30th centile, normal liquor), but a Doppler study of twin A's umbilical artery shows absent end-diastolic flow (AEDF). Twin B is unaffected. That evening, Mrs Anitha calls the emergency line reporting she has noticed reduced movements from one side of her abdomen for the past 4 hours.

DISCUSSION POINTS

  • Absent end-diastolic flow in the umbilical artery at 28 weeks indicates what underlying process? What is the clinical significance, and what management does this Doppler finding require?
  • The patient reports reduced fetal movements. Outline your immediate assessment approach — what investigations would you arrange in the next 30 minutes, and what decision threshold would prompt immediate delivery at 28 weeks?
  • If you decide to administer corticosteroids at 28 weeks, which agent(s) do you use, what is the dose and schedule, and what is the evidence base for their use at this gestational age?
  • Discuss the risks and benefits of immediate delivery vs continued surveillance for twin A at 28 weeks with AEDF. What support services and counselling would you provide to Mrs Anitha and her family?
Click to reveal Trigger 4: Third-Trimester Decision: Delivery Planning (discuss previous trigger first!)

Trigger 4: Third-Trimester Decision: Delivery Planning

Twin A stabilises with intensive surveillance. Both twins survive to 32 weeks. The 32-week USS shows: twin A — EFW 1450 g (10th centile), normal liquor, umbilical artery AEDF now resolved (end-diastolic flow present). Twin B — EFW 1700 g (30th centile), normal. Presentation: twin A vertex, twin B transverse. The obstetric team is planning delivery. A new finding is noted: the placenta is anterior and its lower edge appears to be within 1.5 cm of the internal os on transvaginal USS.

DISCUSSION POINTS

  • How does the placental position finding at 32 weeks change the delivery plan? At what distance from the internal os does the placenta become a 'low-lying placenta' vs 'placenta praevia'? Would you proceed with a trial of labour?
  • Twin B is transverse at 32 weeks. Outline the options for delivering a transverse lie second twin after vaginal delivery of the first twin — which manoeuvres are available, and in what order would you attempt them?
  • What is the recommended optimal delivery timing for MCDA twins (without the complicating placental position finding)? Justify the timing in terms of balancing prematurity risks against the ongoing risks of continuation.
  • Mrs Anitha asks: 'If I need a caesarean section, will I need a blood transfusion?' With the placenta anterior and low, what specific surgical complication should you counsel her about, and what preparations should be made pre-operatively?
Click to reveal Trigger 5: Postoperative Haemorrhage: Applying Blood Product Knowledge (discuss previous trigger first!)

Trigger 5: Postoperative Haemorrhage: Applying Blood Product Knowledge

Elective caesarean section is performed at 34 weeks. During surgery, when the lower segment is incised, there is massive haemorrhage — the placenta is found to be morbidly adherent (placenta accreta spectrum). Estimated blood loss is 2,500 mL. Intraoperatively: BP 75/40 mmHg, Hb 5.8 g/dL, fibrinogen 0.7 g/L, platelets 65,000/µL, PT 30 s. Both neonates are delivered safely.

DISCUSSION POINTS

  • The massive transfusion protocol (MTP) is activated. Describe the 1:1:1 component ratio of the MTP and the physiological rationale for this ratio — why is it not just PRBCs alone?
  • The fibrinogen is 0.7 g/L. Which blood product specifically corrects this deficit, and why is fresh frozen plasma alone insufficient? What fibrinogen target are you aiming for in this obstetric patient, and why is this target higher than the non-pregnant standard?
  • Name four specific complications of massive transfusion and briefly describe how each is monitored and managed in the intraoperative/early postoperative period.
  • The haemorrhage is controlled, but 6 hours postoperatively the patient develops progressive hypoxia and bilateral infiltrates on chest X-ray with a pulmonary artery wedge pressure of 12 mmHg. What is this diagnosis, and how is the management different from fluid-overload-induced pulmonary oedema?

Group Task Assignments

  • Map the progression of this case on a timeline, noting which complications are unique to monochorionic placentation vs which could occur in any twin pregnancy.
  • Create a decision algorithm for a clinician receiving an USS report of 'twin pregnancy with single placenta' at 14 weeks — what questions must be answered and in what order?
  • Produce a blood product reference card for obstetric haemorrhage: product name, component contents, indication, target level to achieve, and key precautions (including the cryoprecipitate vs FFP distinction for fibrinogen replacement).
  • Write a two-minute structured explanation of this case (the diagnosis, complication, and outcome) that could be delivered to a patient at a Year-1 level of health literacy.

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [OG11.1] What is the mechanistic link between monochorionic placentation and twin-to-twin transfusion syndrome, and how does this determine treatment strategy?
  2. [OG11.1] How is chorionicity reliably determined by ultrasound, and why does the gestational age at which USS is performed affect reliability?
  3. [OG11.1] What are the Quintero stages of TTTS, what specific USS finding defines each stage, and how does staging influence management?
  4. [OG10.1] At what distance from the internal os on TVS does low-lying placenta become confirmed placenta praevia, and how does this classification guide delivery planning?
  5. [OG10.2] What is the evidence basis for the 1:1:1 ratio in the massive transfusion protocol, and why is the fibrinogen target in obstetric DIC set at >2 g/L rather than >1 g/L?
  6. [OG10.2] What is TRALI, what is its pathophysiology, and how is it clinically distinguished from transfusion-associated circulatory overload (TACO)?