Between pregnancy biological variability of first trimester markers of Down syndrome and the implications for screening in subsequent pregnancies: an issue revisited

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Abstract
Objectives To assess the level of correlation of first trimester biochemical and biophysical markers of Down syndrome between different pregnancies in the same individual. To assess the impact that between pregnancy biological variability has on the likelihood that women who are at increased risk in a first pregnancy being also at increased risk in a subsequent pregnancy. Methods During a three period women attending the OSCAR clinic at Harold Wood Hospital have had the opportunity to have first trimester screening for Down syndrome and other aneuploidies using the maternal serum biochemical markers free β‐human chorionic gonadotrophin (hCG) and pregnancy associated plasma protein‐A (PAPP‐A) in conjunction with fetal nuchal translucency (NT) thickness and maternal age. Of the 11 1105 women undergoing such screening, the computer records were examined for women who had more than one pregnancy. The results from 1002 women with two normal singleton pregnancies were available for analysis. Marker correlations (as MoM) were established between the pregnancies and the proportion of women likely to be at increased risk in each pregnancy estimated, as was the likelihood of women being at increased risk in both pregnancies. Results For fetal NT there was no correlation between NT MoM in the first and second pregnancy (r = 0.0959, p > 0.10). For maternal serum free β‐hCG MoM a significant correlation was found (r = 0.3976, p < 0.001), as was also found for PAPP‐A MoM (r = 0.4371, p < 0.001). Conclusion The implication for such between pregnancy marker association is that women who have an increased risk of Down syndrome in one pregnancy are two or three times more likely to repeat this event in their next pregnancy. This information may be useful in counselling women when undergoing first trimester screening in a subsequent pregnancy. Copyright © 2002 John Wiley & Sons, Ltd.

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