Cystic fibrosis is an autosomal recessive disease. The cystic fibrosis carrier rate is 1/25 in whites (non-Hispanic) and 1/29 in Ashkenazi Jews. Therefore, these couples should receive preconception counseling and be offered testing. Other couples that should be offered preconception counseling include the reproductive partners of individuals who have CF and individuals with a family history of CF. In fact, ACOG now recommends that CF screening also be offered to couples in lower risk categories. When both partners are identified as carriers of the CF mutation during early pregnancy, prenatal diagnosis should be offered. An amniocentesis can be done at 15-20 weeks, so that the couple can consider termination of pregnancy if the fetus has CF. Another option is to offer chorionic villus sampling at 10-12 weeks for prenatal diagnosis.
Dr. Socol also discussed first-trimester screening for aneuploidy. Although the multiple marker screening (double/triple/quad screening) is the standard of care for the second trimester, much ongoing research concerns first-trimester screening. Therefore, couples could soon have more answers regarding the chromosomal makeup of the fetus earlier in pregnancy.
The measurement of fetal nuchal translucency (NT) thickness at 10-14 weeks gestation has been combined with maternal age to provide a screening method for trisomy 21. Free beta human chorionic gonadotrophin (B-hCG) and pregnancy-associated plasma protein-A (PAPP-A) can be combined with NT and maternal age for increased trisomy 21 detection at 10-14 weeks. According to K. Nicholaides from King's College Hospital in London, the detection rate of chromosomal defects can be 90%. The problem with using NT, however, is that the measurement of the fetal NT is subjective and depends on the skill of the ultrasonographer. Dr. Socol discussed an abstract from the 2002 Society of Maternal-Fetal Medicine meeting that demonstrated promising results for first-trimester aneuploidy screening using maternal age, biochemical blood tests (PAPP-A and free B-hCG) and NT. The First and Second Trimester Evaluation of Risk (FASTER) trial is an NIH trial being conducted at 11 medical centers nationwide that is studying screening for Down syndrome and other serious birth defects during the first and second trimester of pregnancy. It is hoped that this study will validate the work of Nicholaides in London.
Medscape Ob/Gyn. 2002;7(1) © 2002 Medscape
Cite this: Highlights in Obstetrics From the 50th Annual Meeting of The American College of Obstetricians and Gynecologists - Medscape - Jun 12, 2002.