Correlation between estimated fetal weight and weight at birth in infants with gastroschisis and omphalocele

Background: An accurate estimated fetal weight (EFW) calculated with traditional formulae in cases of abdominal wall defects (AWDs) can be challenging. As a result of reduced abdominal circumference, fetal weight may be underestimated, which could affect prenatal management. Siemer et al. proposed a formula without the use of abdominal circumference, but it is not used in our protocols yet. Objectives: Our aim was to evaluate the correlation of EFW and birth weight in fetuses with AWD by using Hadlock 1, Hadlock 2, and Siemer et al.'s formulae. Our secondary goal was to evaluate how often fetuses classified as small for gestational age (SGA) were in fact SGA at birth. Study design: This was a retrospective cohort study of gestations complicated by gastroschisis and omphalocele at two tertiary-care centers in Brazil and Italy during an 8-year period. Of a total of 114 cases, 85 (44 cases of gastroschisis and 41 cases of omphalocele) met our criteria. Results: The last prenatal scan was performed 5.2 (+/- 4.1) days before birth. The mean gestational age at birth was 37.2 (+/- 1.8) weeks. Correlation of EFW with birth weight was calculated with the three formulae with and without adjustment for weight gain between scan and birth, with the use of the Spearman coefficient. The correlation between EFW and weight at birth was positive according to all three formulae for the infants with gastroschisis. This finding was not confirmed in the infants with omphalocele. All formulae overestimated the number of SGA cases: although only 17.6% of fetuses were actually SGA at birth, the Hadlock formulae had classified nearly 35% of them as SGA, and Siemer et al.'s formula, 15.3%. Conclusion: All three formulae yielded a good correlation between EFW in the last scan and birth weight in the infants with gastroschisis but not for those with omphalocele. Cases of SGA were overestimated.

Automated summary

The objective of this study was to evaluate the correlation between estimated fetal weight (EFW) calculated using different formulae and birth weight, as well as to assess the accuracy of classifying fetuses as small for gestational age (SGA) at birth. The results showed a good correlation between EFW and birth weight for infants with gastroschisis, but no correlation for those with omphalocele. All formulae overestimated the number of SGA cases.