Comparing the relationship between ultrasound-estimated fetal weight and birthweight in cohort of small for gestational age fetuses

Introduction Small‐for‐gestational‐age (SGA) confers a higher perinatal risk of adverse outcomes. Birthweight cannot be accurately measured until delivery, therefore accurate estimated fetal weight (EFW) based on ultrasonography is important in identifying this high‐risk population. We aimed to establish the sensitivity of detecting SGA infants antenatally in a unit with a selective third‐trimester ultrasound policy and to investigate the association between EFW and birthweight in these babies. Material and methods A retrospective cohort study was conducted on non‐anomalous singleton pregnancies delivered after 36 weeks of gestation where SGA (<10th percentile) was diagnosed at delivery. The EFW at the time of the third‐trimester ultrasound scan was recorded using standard Hadlock formulae. Results In 2017, there were 8392 non‐anomalous singleton pregnancies live born after 36 weeks, excluding late bookers. 797 were live‐born SGA <10th percentile for birthweight and 464 <5th percentile, who met our inclusion criteria. The antenatal detection rate of SGA was 19.6% for babies with birthweight <10th percentile and 24.1% <5th percentile. There was a significant correlation between the EFW and birthweight of fetuses undergoing ultrasound assessment within 2 weeks of delivery (P < .001, r = 0.73 (Pearson correlation). For these cases, EFW was greater than the birthweight in 65% of cases. After adjusting all EFWs using the discrepancy between EFW and actual birthweight for those babies born within 48 hours of the scan, the mean difference between the birthweight and adjusted EFW 7 days before delivery was 111 g (95% CI 87‐136 g) and at 14 days was 200 g (95% CI 153‐248 g). Despite adjusting the EFW, 61/213 cases (28.6%) apparently lost weight between the ultrasound scan and delivery. Conclusions Small‐for‐gestational‐age infants with a birthweight <10th percentile are poorly identified antenatally with little improvement for those <5th percentile. In SGA babies, ultrasound EFW overestimated birthweight. Discrepancies between birthweight and EFW are not explicable only by the limitations of third‐trimester sonography, a reduction in fetal weight close to delivery in a proportion of liveborn SGA babies is plausible

Contemporary experience of polyhydramnios: a single-centre experience

Introduction: Polyhydramnios is common; the majority of cases are idiopathic, but maybe associated with fetal abnormality. Literature suggests the volume of amniotic fluid discriminates idiopathic from pathological polyhydramnios but is not unanimous. We assessed fetal anomaly incidence amongst women with polyhydramnios and the role of discriminatory variables in identifying pathological cases. Methods: Retrospective observational cohort study at an inner-city London fetal medicine centre. Records for patients referred and/or diagnosed with polyhydramnios were reviewed as well as maternal/fetal demographics, amongst singleton pregnancies using the Astraia™ database from January 2015-2016. Estimated fetal weight was calculated using the Hadlock model (biometry undertaken at diagnosis). Student's t-test/one-way ANOVA compared means; chi-squared tests compared proportions. Results: 120 cases were identified. 36 (30%) had fetal abnormality. There was no difference in AFI between fetuses with an abnormality and without (26.7 vs 25.2 cm, P = 0.22). AFI was normalised for weight (AFI (cm)/estimated fetal weight (kg)): AFI/kg was significantly different between cases with fetal abnormality and without (24.4 vs 16.7 cm/kg, P < 0.001) - incidence of abnormality increased with increasing AFI/kg (P = 0.007). Early gestational diagnosis was associated with higher rates of anomaly (P = 0.004). Differences in AFI/kg between those with and without abnormality were not significant when adjusted for gestation. AFI was significantly higher in cases of abnormality diagnosed at later gestation (P = 0.005). Conclusion: Excess volume of amniotic fluid alone does not denote abnormality. Earlier gestations and higher AFI/kg corresponded with significantly increased rates of anomaly. However, the latter is a result of confounding by gestation, which is closely correlated with fetal weight