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In accordance with a previous protocol, a second cohort of 254 mothers with a history of previous neural tube defect (NTD) births was before a subsequent conception and continued until the time of the second missed menstrual period. There were 2 NTD recurrences (0.9% of 234 infants/fetuses examined), which is significantly fewer than the 11 NTD recurrences (5.1% of 215 infants/fetuses examined) born to 219 unsupplemented (US) mothers in the same centres over the same period. When the data for the two cohorts were combined, the overall recurrence rates were 0.7% for 454 fully supplemented (FS) mothers and 4.7% for 519 US mothers. The recurrence rates after 1 previous NTD were 0.5% for FS and 4.2% for US mothers: after 2 or more previous NTDs, 2.3% for FS and 9.6% for US. There were no recurrences among the offspring of a further 114 mothers whose duration of supplementation fell short of the full regimen (partially supplemented, PS).

Maternal serum-alpha-fetoprotein (A.F.P.) levels were compared throughout pregnancy in women bearing fetuses with severe neural-tube defects and in control women. From the second trimester onwards, the former group had higher levels than the controls, but the difference was not always clear-cut, rendering such a test less reliable than assay of the amniotic-fluid A.F.P. The blood-A.F.P. levels of seven anencephalic fetuses were normal for their gestational age, suggesting that there is no increased synthesis of A.F.P. in fetuses with severe neural-tube defects.

our experience as a regional genetics center could be of interest to those concerned with the gestational age at the termination of pregnancies for medical reasons. Here there are 4 sets of indications for termination--neural tube defects, unbalanced chromosome disorders, serious and untreatable X-linked disorders, and grave and incurable inborn errors of metabolism. Most determinations for neural tube defects are performed earlier than those for chromosome abnormalities because the alpha fetoproteins assay is done directly on the fluid, while tissue culture and cytology are lengthy procedures. Specific biochemical errors can be quickly identified in those cases where tests can be done directly on the fluid or be based on modest numbers of amniotic cells, but when the specific tests require a large number of cultured cells, a long time lag may be involved. The figures show not what happens under theoretically ideal circumstances, but the real life pattern which emerges in the face of such variables as woman's booking habits, amniocentesis failure, culture failure, and the need for repeat amniocentesis.

The sex ratio of 147 fetuses with presumed multifactorial neural tube defect (NTD) was studied. Overall, the ratio (males:females) was 0.73 with expected female excess. However, when the NTDs were subdivided according to the site of the lesion, the sex ratios varied. Total craniorachischisis, anencephaly with cervical spina bifida, holoacrania, and thoracic spina bifida showed a greater female excess than that overall; the sex ratio for meroacrania was close to unity, while that for low spinal lesions, particularly those involving the sacrum, showed an extreme bias towards males. These findings are related to the mode of formation of the neural tube. Females seem prone to defects of neurulation and males to defects in canalization. An explanation for these findings is suggested in possible sex differences in rate of early embryonic development.