Prenatal detection of neural tube defects

Abstract EN

-This work was conducted to provide a second trimester prenatal diagnosis by non-invasive means of identifying pregnant females at an increased risk of NTDs.

Combination of several different markers were used for screening, which included AFP, HCG, uE3, with evaluation of the benefits and limitations of the screening tests, as well as their sensitivity and specificity as a reliable prenatal screening test, separately or in combination, compared to ultrasonographic examination.

In this study, 50 Egyptian females with singleton pregnancy at high-risk for NTDs were selected (having previous child with NTDs).

The age of participants ranged between 18-41 years (Mean 28.46 ± 7.05 SD) at the expected date of delivery, their gestational age at the time of test ranged from 14-22 Weeks (Mean 17.76 ± 2.36 SD).

They were screened by the “triple test’’.

Maternal serum AFP, HCG and uE3 were assayed in relation to fetal gestational age using commercially available immunoassay kits and median values were established for each of the three analytes.

The values were expressed in multiples of median (MOM), taking into account the increase in AFP, uE3 and the decrease in HCG with increasing gestational age.

The sensitivity of AFP assay alone was found to be 87.5 % and specificity 96.9 % for open NTDs.

In contrast to the contention at unconjugated estriol is not useful in screening, the results of the present study suggest that measurement of uE3 is useful for prenatal detection of anencephaly, as well as Down syndrome, with a sensitivity of 75% and specificity 89.2%.

Thorough ultrasonographic evaluation was done for accurate dating of gestational age and to exclude any apparent fetal structural abnormalities, as well as targeted ultrasonography after the detection of abnormal triple screen.

When the key variables influencing assay results are considered (as maternal weight, race, gestational week, maternal age, fetal immaturity) the degree of efficacy of the combined three markers screening facilitates detection of neural tube defects with the sensitivity of 100% in anencephaly and meningo- myelocele and 75% in other leaking defects.

The specificity was 96.0%, and the detection rate of 75%-100% at 2% false positive rate, which exceeds the sensitivity and specificity rates of ultrasonic examination and gives the opportunity of earlier detection.

It is recommended that all women of childbearing age should receive 0.4 mg folic acid daily to reduce the risk of having NTDs and those at high risk should receive 4.0 mg folic acid daily and screened by triple test at 14- 22 weeks of pregnancy.