Cystic fibrosis-prenatal diagnostics

Question

Dear team,

I would like to know whether I can test my unborn child for cystic fibrosis during pregnancy and if so, with which test?

Thank you for your answer.

Answer

Dear questioner,

we cannot tell from your question for which reason you would like to test your child. Is it possible that both parents are heterozygous for the cystic fibrosis (CF) mutation (i.e., healthy carriers of the disease)? Did you and your partner do genetic tests? Do you already have a child that has CF? Are there any relatives with CF? The answers to these and other questions would make a decision about further diagnostic procedures during pregnancy easier.

Routinely, organ screenings are performed during pregnancy, particularly between the 19th and 22nd week. At this point, the complete foetus is best visible. One can therefore document the regular development of body parts and organs and perform further diagnostics in case of any irregularities. Using ultrasound, for instance, one can diagnose hyperechogenic bowel, a sonographic hint that can occur in a number of prenatally relevant diseases such as CF. Further diagnostics can include chorionic villus sampling (CVS) between the 8th and 13th week and later amniocentesis (test of the amionic fluid) between the 15th and 18th week.

In chorionic villus sampling (CVS), a tissue sample of the embryo’s future placenta (chorionic villi) is taken. This is aspirated from the uterus with a hollow needle via the vagina and the cervix channel and tested genetically. If this biopsy is done very early, there might not be enough tissue present yet, so that the ideal time for this test is after the 11th week.

In an amniocentesis (test of the amionic fluid), amionic fluid is taken from the uterus by puncture of the uterine cavity via the mother’s abdominal wall. Here, too, the problem is that there has to be a certain amount of amnionic fluid in order to be able to draw an appropriate amount. This is actually the case only after the 15th, or better yet after the 16th week.

“Advance results” are available for both methods (chorionic villus sampling and amniocentesis) already after two days. The final results will take about 8 days. In both tests, the embryo’s/foetus’ complete chromosome set is tested and one can then tell whether a child will have CF or not. If either of the tests confirms CF (waiting time up to 14 days), the couple then has to decide whether it would like to continue the pregnancy or terminate it.

Both methods of prenatal diagnostics bear a 1-2% risk of leading to miscarriages. Therefore, a couple should be sure that the result also affects the continuation of the pregnancy, since otherwise it would mean taking an unnecessary risk. After obtaining the test results, the woman is at least in the 14th week (CVS) or even further along (amniocentesis). An easy termination like before the 12th week is no longer possible then. The cervix is widened with the help of drugs and the woman has to wait for the rejection of the foetus.

We would be glad if our explanations help you a bit. At any rate, we recommend that you talk to your treating gynaecologist and perhaps also with a further doctor of your confidence in detail about this. We hope that the information we have provided here will help you for these consultations.

Kind regards,
Dr. Christina Smaczny and Dr. Anja-Undine Stücker

19.07.2012