The cohort in one paragraph
Of the seventeen babies indicted in the original trial and the retrial, at least seven were from twin pregnancies and three were from a single triplet pregnancy. That is a substantial over-representation of multiple pregnancies relative to the neonatal unit’s overall admission profile. The prosecution narrative treated this, where it treated it at all, as a coincidence of which patients happened to be on the unit during the cluster period. The obstetric literature reads it very differently.
Why multiple pregnancies are higher-risk
- Preterm delivery. Over half of twin pregnancies deliver before 37 weeks; most triplet pregnancies deliver before 34 weeks. Preterm birth is the single largest risk factor for neonatal morbidity and mortality.
- Placental insufficiency. Two or three fetuses sharing placental resources can lead to one or more being growth-restricted, with reduced reserves at birth.
- Twin-to-twin transfusion syndrome (TTTS). In monochorionic twins, placental vascular imbalance can cause severe asymmetry between the two fetuses. A surviving twin after a sibling death in utero is at elevated risk of poor outcomes.
- Selective intrauterine growth restriction (sIUGR). Another multiple-pregnancy-specific condition in which one fetus grows substantially less than the other. Growth-restricted infants are physiologically more fragile than their non-restricted peers.
- Anti-phospholipid syndrome (APS). An autoimmune condition more common in women with recurrent pregnancy complications. Babies born to APS-affected pregnancies carry their own risk profile, particularly around thrombosis.
- Triplet-specific risks. Triplet pregnancies carry several-fold higher perinatal mortality than singleton pregnancies, even at optimal gestation.
How the indicted cohort’s cases map onto these risks
Without using names or identifying details, the published obstetric record and the Panel’s case-by-case review together show the indicted cases included:
- A surviving twin who collapsed after a sibling’s death on the unit — a specifically recognised high-risk presentation in twin pregnancies.
- A growth-restricted twin with independently documented antenatal concerns.
- A term triplet set whose two brothers died within 24 hours of each other, consistent with the known elevated risk profile of triplet pregnancies at term.
- Babies born to mothers with documented antenatal complications including APS, TTTS-pattern abnormalities, and sIUGR.
Sarah Hawkins’s long-form analyses (hosted on this site) walk through each of these categories in detail, with cited obstetric sources. See the twin-mother letter and triplets to singletons.
Why this matters for the shift chart
The shift-rota chart shown to the jury plotted 25 “suspicious” events against nursing-shift attendance. The 25 events were selected in part because they looked suspicious in retrospect; the cohort over-represented multiple pregnancies, which over-represented the structurally-higher-risk patients on the unit.
In other words, the chart selected for two things at once: Letby’s presence and a higher-risk patient cohort. A chart constructed to isolate one of those variables from the other would look quite different from the one the jury saw. Prof. Richard Gill has made this point explicitly in his “tale of two Lucies” lecture.
Why this matters for the medical evidence
Independent obstetricians reading the casebook have been increasingly public in saying that trial expert evidence on causation did not adequately canvass the multiple-pregnancy-specific explanations for deterioration. In a triplet who collapses at term, the paediatric differential should include triplet-pregnancy complications as a primary hypothesis. In a surviving monochorionic twin whose sibling has just died, the differential should include all the TTTS-pattern downstream consequences. These differentials were not systematically put to the jury.
The wider argument
Properly baselined against a multiple-pregnancy cohort on a struggling Level 2 unit with a superbug outbreak and staffing shortages, the 2015–16 Countess of Chester cluster is not, in the epidemiological sense, anomalous. It is what a unit in that situation is expected to produce. That does not itself prove the cluster is entirely attributable to natural causes and systems failures, but it means the criminal-causal hypothesis is, statistically speaking, unnecessary to explain the data.