Placentation in SCD

• In a recent study on placentation in SCD (169), of the 72 placentas from women with SCD and pregnancies of more than 20 weeks for which histopathology was available, 50 (69%) had placental pathology and 29 (40%) had maternal vascular malperfusion (MVM). In non-SCD healthy pregnancies, MVM is found in 7–8% of placentas. Outside of SCD, MVM has been linked to conditions associated with placental insufficiency, such as pre-eclampsia. The presence of MVM was associated with adverse pregnancy outcomes (attributable to placental insufficiency), including small for gestational age, iatrogenic preterm birth, and stillbirth. These outcomes were seen in 79% of women with MVM, while the risk of adverse outcomes in a low-risk pregnant population with MVM has been reported at ~47% (170). The study authors proposed that the high rates of MVM observed may suggest that factors inherent in SCD, that remain as yet unidentified, may potentiate the placental disease sometimes present in unaffected healthy women. Increased risk of small-for-gestational age and stillbirth in women with SCD
• Maternal SCD is associated with increased odds of stillbirth (pooled OR 4.05; 95% CI 2.69 to 6.32; p<0.001), intrauterine growth restriction (pooled OR 2.79, 95% CI 1.85 to 4.21), perinatal mortality (pooled OR 3.76, 95% CI 2.34 to 6.06), and low birthweight (pooled OR 2.00, 95% CI 1.42 to 2.83) (7). These outcomes are consistent across low- and high-income settings (7). The pathophysiology behind these adverse outcomes is multifactorial, but is likely due in part to placental insufficiency.
• Fetal growth restriction (due to any cause) is associated with an increased risk of stillbirth and perinatal death. Outcomes are often dependent on the degree of growth restriction, with the highest risk for fetuses at less than the third percentile or with doppler ultrasound abnormalities. Identification of growth restriction and antenatal fetal surveillance can help predict and prevent stillbirth by informing judgements on the timing of birth. Type of monitoring
• Depending on the setting, the type of fetal monitoring may include ultrasound, fetal phonocardiogram, one-dimensional Doppler, cardiotocography (including non-stress test, contraction stress test, acoustic stimulation), fetal electrocardiogram and fetal magnetocardiography, at a frequency that is related to the monitoring method and predictive value for stillbirth. Timing of monitoring
• Modelling to estimate the effect of the interval between examinations on fetal growth restriction in the general pregnant population suggests that taking measurements at least three weeks apart may minimize false positive rates (171). False positive rates were higher when the first scan was performed at 36 weeks (compared to first scan at 32 weeks) (171). Accuracy of ultrasound in detecting fetal growth restriction
• Over time, there have been several improvements in ultrasound technologies including high-resolution ultrasonography, linear transducer, radiant flow, three-/four-dimensional ultrasound, and artificial intelligence (172). The accuracy of ultrasound estimated fetal weight has improved in the last decade, though a lack of consistency remains evident (173). Key sources of inaccuracy identified in a systematic review included difficulties obtaining accurate fetal measurements in late gestation. The remaining barriers were operator dependent, including lack of experience and insufficient training and audit (173). Interventions in the context of fetal growth restriction
• There are no proven interventions for small for gestational age and fetal-growth restriction other than birth of the baby. However, identification of fetal-growth restriction can trigger assessment of fetal wellbeing, including discussion of fetal movements and cardiotocography. Maternal assessment can also be offered, including blood pressure and proteinuria assessment. Adverse effects associated with increased fetal monitoring
• The advantages of fetal monitoring need to be balanced against any potential adverse effects. For example, certain findings may be considered indications for induction. WHO notes that induction of labour can increase the risk of iatrogenic complications (i.e. inadvertent prematurity) and use of resources (i.e. induction agents, health workers, facility preparedness) (174).
• Though antenatal ultrasound is largely seen as positive, long-term adverse psychological and reproductive consequences have been reported for some women (175). Costs
• The GDG acknowledged the need to consider the cost of fetal monitoring for women, as there may be increased out-of-pocket costs.
• In some low-income settings, access to ultrasound may be limited due to lack of staff and other resources, as well as the costs incurred for women and the distance they would have to travel to attend appointments (175).