Knowledge Gaps and Emerging Research Areas in Intrauterine Growth Restriction-Associated Brain Injury

Objective To assess the main risk factors associated with stillbirth in a multiethnic English maternity population. Design Cohort study. Setting National Health Service region in England. Population 92 218 normally formed singletons including 389 stillbirths from 24 weeks of gestation, delivered during 2009-11. Main outcome measure Risk of stillbirth. Results Multivariable analysis identified a significant risk of stillbirth for parity (para 0 and para ≥3), ethnicity (African, African-Caribbean, Indian, and Pakistani), maternal obesity (body mass index ≥30), smoking, pre-existing diabetes, and history of mental health problems, antepartum haemorrhage, and fetal growth restriction (birth weight below 10th customised birthweight centile). As potentially modifiable risk factors, maternal obesity, smoking in pregnancy, and fetal growth restriction together accounted for 56.1% of the stillbirths. Presence of fetal growth restriction constituted the highest risk, and this applied to pregnancies where mothers did not smoke (adjusted relative risk 7.8, 95% confidence interval 6.6 to 10.9), did smoke (5.7, 3.6 to 10.9), and were exposed to passive smoke only (10.0, 6.6 to 15.8). Fetal growth restriction also had the largest population attributable risk for stillbirth and was fivefold greater if it was not detected antenatally than when it was (32.0% v 6.2%). In total, 195 of the 389 stillbirths in this cohort had fetal growth restriction, but in 160 (82%) it had not been detected antenatally. Antenatal recognition of fetal growth restriction resulted in delivery 10 days earlier than when it was not detected: median 270 (interquartile range 261-279) days v 280 (interquartile range 273-287) days. The overall stillbirth rate (per 1000 births) was 4.2, but only 2.4 in pregnancies without fetal growth restriction, increasing to 9.7 with antenatally detected fetal growth restriction and 19.8 when it was not detected. Conclusion Most normally formed singleton stillbirths are potentially avoidable. The single largest risk factor is unrecognised fetal growth restriction, and preventive strategies need to focus on improving antenatal detection.

GABA(A) (gamma-aminobutyric acid type A) receptors mediate most of the 'fast' synaptic inhibition in the mammalian brain and are targeted by many clinically important drugs. Certain naturally occurring pregnane steroids can potently and specifically enhance GABA(A) receptor function in a nongenomic (direct) manner, and consequently have anxiolytic, analgesic, anticonvulsant, sedative, hypnotic and anaesthetic properties. These steroids not only act as remote endocrine messengers, but also can be synthesized in the brain, where they modify neuronal activity locally by modulating GABA(A) receptor function. Such 'neurosteroids' can influence mood and behaviour in various physiological and pathophysiological situations, and might contribute to the behavioural effects of psychoactive drugs.

Ionic currents and the network-driven patterns they generate differ in immature and adult neurons: The developing brain is not a "small adult brain." One of the most investigated examples is the developmentally regulated shift of actions of the transmitter GABA that inhibit adult neurons but excite immature ones because of an initially higher intracellular chloride concentration [Cl(-)](i), leading to depolarizing and often excitatory actions of GABA instead of hyperpolarizing and inhibitory actions. The levels of [Cl(-)](i) are also highly labile, being readily altered transiently or persistently by enhanced episodes of activity in relation to synaptic plasticity or a variety of pathological conditions, including seizures and brain insults. Among the plethora of channels, transporters, and other devices involved in controlling [Cl(-)](i), two have emerged as playing a particularly important role: the chloride importer NKCC1 and the chloride exporter KCC2. Here, the authors stress the importance of determining how [Cl(-)](i) is dynamically regulated and how this affects brain operation in health and disease. In a clinical perspective, agents that control [Cl(-)](i) and reinstate inhibitory actions of GABA open novel therapeutic perspectives in many neurological disorders, including infantile epilepsies, autism spectrum disorders, and other developmental disorders.