An introduction to the circumstance of the death of Baby I, where so called expert witnesses boil almost three months of progressive deterioration of a critically ill preterm neonate, into four single events. They do so in defiance of our knowledge of the cumulative effects of disease and its relationship to mortality and the extremely high mortality of neonates born after premature rupture of membranes at or before 21 weeks gestation.

https://tattle.life/wiki/lucy-letby-case-8/#child-i

Very premature rupture of membranes (PPROM) at 21 weeks gestation has significant effects on neonatal mortality and morbidity.

The survival rate for neonates born after PPROM at less than 24 weeks gestation is generally low. Studies indicate that survival with rupture of membranes at less than 21 weeks of gestation is rare. The survival rate to discharge can be highe with expectant management with one study claiming that 26% of babies survived to discharge from hospital when PPROM occurred before 23 weeks gestation.

Neonates who survive PPROM at such early gestational ages often experience severe morbidity. Studies have shown that among survivors, a high percentage experience severe morbidities such as intraventricular hemorrhage, retinopathy of prematurity, bronchopulmonary dysplasia, and necrotizing enterocolitis. For instance, one study reported that 77.8% of survivors experienced severe morbidity at the time of discharge.

The duration of the latency period (time between onset of PPROM and birth) is a critical factor. Longer latency periods are associated with better survival rates and fewer severe morbidities. For example, a study found that later gestational age at PPROM and longer latency periods were significantly associated with survival without severe morbidities, but these studies do not include premature rupture of membranes occurring at 21 weeks gestation. 

The gestational age at birth also plays a crucial role. Babies born at more advanced gestational ages tend to have better outcomes. For instance, one study found that survivors were born at more advanced gestational ages compared to non-survivors.

In summary, PPROM at 21 weeks gestation is associated with high neonatal mortality and morbidity rates. 

Citations:

Neonatal outcomes in women with preterm premature rupture of membranes at periviable gestational age

Preterm Premature Rupture of Membranes Between 14 and 24 Weeks of Gestation Outcomes With Expectant Management

Preterm infant outcomes in relation to the gestational age of onset and duration of prelabour rupture of membranes: a retrospective cohort study

Preterm prelabour rupture of membranes before 23 weeks’ gestation: prospective observational study

Prognosis of preterm premature rupture of membranes between 20 and 24 weeks of gestation: A retrospective cohort study