Uptake of prenatal screening for chromosomal anomalies: impact of test results in a previous pregnancy.

AIM: To assess whether the uptake of prenatal screening for trisomy 21 in a subsequent pregnancy is influenced by being classified in the 'increased risk' or 'not at increased risk' group in the first pregnancy.

SETTING

District General Hospital Maternity Unit.

METHODS

Amongst a group of women attending for maternity care at this hospital, the maternity records were examined to find women having at least two pregnancies. Any prenatal screening record for each pregnancy was retrieved from the prenatal screening database. Prenatal screening for trisomy 21 was by a combination of maternal serum alpha-fetoprotein (AFP) and free beta-human chorionic gonadotrophin (beta-hCG) in the second trimester and by maternal serum free beta-hCG and pregnancy-associated plasma protein-A (PAPP-A) and fetal nuchal translucency (NT) thickness in the first trimester. Women were stratified according to their trisomy 21 risk into an 'increased risk' group (1: <250 in the second trimester and 1: <300 in the first trimester) or 'not at increased risk' group based on their first pregnancy. In a second pregnancy, the records were examined to see if the mother accepted prenatal screening in the second pregnancy. The rate of acceptance of screening in a subsequent pregnancy, depending on whether 'at increased risk' or 'not at increased risk' in the first pregnancy, was examined using chi square tests.

RESULTS

In the second trimester study, 4601 women were identified with two pregnancies during the study period. Of these, 4559 women had prenatal screening in a subsequent pregnancy. Initially, 273 women were identified in the high-risk group, and of these 252 (92.3%) elected to have prenatal screening in a subsequent pregnancy. This compared with 4307 of 4328 (99.5%) women in the low-risk group. In the first trimester study, 1077 women were identified with two pregnancies during the study period. Of these, 1072 had prenatal screening in a subsequent pregnancy. Initially, 60 women were identified in the high-risk group, and of these 56 (93.3%) elected to have prenatal screening in a subsequent pregnancy. This compared with 1016 of 1017 (99.9%) in the low-risk group. Statistically, there was no difference between the rate of declining prenatal screening in a second pregnancy amongst those in the high-risk group in a first pregnancy or those in the low-risk group (p = 0.429 for second trimester screening and p = 0.794 for first trimester screening). Similarly, no difference could be demonstrated between rates when screening in the first or second trimester (p = 0.961) for those in the high-risk group.

CONCLUSION

Despite the understandable anxiety associated with being identified in the high-risk group (as a false positive finding) in a previous pregnancy, this did not seem to deter women from accepting prenatal screening in a subsequent pregnancy.