Prenatal Ultrasound Parameters of Twins with Sagittal Suture Craniosynostosis Question Mechanical Constraint as the Leading Cause

Background: Multiple pregnancy is a known predisposing factor for sagittal suture synostosis, and intrauterine constraint has been suggested as a potential cause. This study evaluates prenatal images of single and multiple pregnancies of children with sagittal suture synostosis to assess the possible pathogenesis. Materials and Methods: Prenatal ultrasound data of scaphocephaly twins treated at Erasmus MC was retrieved retrospectively. The head circumference, cephalic index (CI), and biparietal diameter (BPD) were analyzed. Data were compared with the nonaffected sibling, singletons with scaphocephaly, and to general fetal growth reference values. Results: Data of 8 twin pregnancies with 10 cases of scaphocephaly was gathered. For the head circumference no difference was found between affected fetuses and reference values throughout pregnancy. For the BPD a reduced growth was found, compared with control values. The growth curve for the CI of the affected twins is lower from the start and declines over time. When comparing affected fetuses to nonaffected fetuses, the same differences for the BPD and CI were found as compared with controls. No differences in growth parameters were found between the nonaffected siblings and reference values, nor between the affected scaphocephaly twins and singletons with scaphocephaly. Conclusions: Scaphocephaly in twin pregnancy develops early on in pregnancy, similar to singleton pregnancy, making the theory of constraint as a cause less likely. The development of scaphocephaly in twins is likely to be attributed to the same disturbed developmental processes in suture development as in singletons, and not to mechanical constraint.