ASSOCIATED MALFORMATIONS IN INFANTS AND FETUSES WITH UPPER OR LOWER NEURAL-TUBE DEFECTS

The paper describes associated malformations in infants born with neur al tube defects (N = 3,809) from three large malformation registers an d in fetuses aborted because of a diagnosed neural tube defect (N = 74 8) from two of the registers. In infants, upper spina bifida and encep halocele are more often associated with non-neural malformations than anencephaly or lower spina bifida. Aborted fetuses with spina, bifida or encephalocele have associated malformations registered more often t han infants with those neural tube defects, but the opposite is true f or anencephaly. The degree of detail of the investigation of an aborte d specimen or a perinatally dead infant will contribute to such differ ences but they can also depend on the fact that prenatal detection may be facilitated by the simultaneous presence of other malformations li ke body wall defects, Also, fetuses with many malformations may be mor e prone to abort spontaneously late in pregnancy. Variable prenatal di agnosis may, therefore, explain population differences in the pattern of associated malformations. The type of associated malformation diffe rs with the level of the neural tube defect: this could be due to diff erent causal mechanisms or be a question of cranio-caudal level and/or timing. For limb reduction defects, however, we did not find any asso ciation between upper limb and upper neural tube defects or lower limb and lower neural tube defects. These findings together with other epi demiological data support the idea that upper and lower neural tube de fects may have different significance in epidemiological studies and s hould be treated separately. (C) 1998 Wiley-Liss, Inc.