The effect of increased maternal body habitus on image quality and ability to identify fetal anomalies at a routine 18‐20‐week morphology ultrasound scan: A narrative review

The number of obese pregnant women is increasing. Increased maternal body habitus is related to greater maternal health risks and an increased risk of fetal anomalies. The 18-20-week morphology scan is a routine clinical tool to detect fetal viability, anomalies, gestational age and number. Suboptimal ultrasound visualisation (SUV) affecting image quality increases with larger body habitus. This results in longer scanning times, incomplete and repeat scans, misdiagnosis, sonographer injuries and patient disappointment. This review aims to establish the effect increased maternal body habitus has on ultrasound image quality, specifically, the relationship between maternal body habitus and the 18-20-week morphology scan and detection of fetal anomalies. Inability to assess fetal structures due to SUV creates great challenges for the health system, imaging departments and patients. Studies have used different variables to measure the effect SUV has on the detection of fetal anomalies in obese women such as prenatal/neonatal comparisons, scan completion rates, the number of repeated scans and subjective judgements about diagnostic image quality. Some studies also included other influences such as fetal lie or placental position. Most studies concluded that a linear relationship exists between increased body habitus and decreased detection of fetal anomalies due to SUV particularly cardiac structures