Sophisticated genetic testing can help you plan for baby
Parents-to-be who are concerned about whether their unborn child has, or is at risk for, genetic disorders have several options during pregnancy, said Cape Cod Hospital Obstetrician/Gynecologist Joshua Lupton, MD. And, parents can have their questions answered locally on Cape Cod.
“We offer screening and diagnostic testing at our practice,” he said.
Screening tests indicate if a fetus is at risk for developing a disorder. Diagnostic tests determine if the child has a disorder. According to the American College of Obstetricians and Gynecologists (ACOG), parents can be screened prior to or during pregnancy to see if they may be carriers of some genetic defects. Usually this is done if either parent has a genetic disorder in their family history.
Dr. Lupton said most genetic disorders are autosomal recessive, meaning that both parents would have to carry the defect for it to be expressed in their child. Even if both parents are carriers, the odds are against having a child with the genetic disorder, Dr. Lupton said.
“There’s only a one in four chance that the baby will be affected,” he said.
Among the diseases that prenatal screening can detect are:
- Cystic fibrosis - the most common life-limiting disease among Caucasians that is autosomal recessive, according to the National Organization for Rare Disorders.
- Spinal muscular atrophy - another autosomal recessive disorder, a leading genetic cause of death in early childhood, according to the SMA Foundation.
- Fragile X syndrome - a dominant mutation linked to the X chromosome, which causes developmental issues, including learning problems and cognitive impairment.
During pregnancy, the mother’s blood can be tested during the first and second trimesters and then combined with the results of ultrasound exams of the developing baby to determine if various defects exist, including Down syndrome, Edwards syndrome and neural tube defects, such as spina bifida, according to ACOG.
In another procedure, called amniocentesis, a syringe is used to extract a sample of fluid that surrounds the child in the amniotic sac. The fluid contains fetal cells, which can then be examined. It is usually done between 15 and 20 weeks of pregnancy, according to the ACOG.
“Amniocentesis is the gold standard,” Dr. Lupton said. “Risks are very, very low.”
A less invasive procedure, called cell-free DNA, relies on a sample of the mother’s blood to obtain the child’s genetic information from cells shed from the placenta that are present in the mother’s bloodstream.
“Placental cells – 99 percent of the time represent fetal DNA,” Dr. Lupton said.
Another screening option is chorionic villus testing, or CVS, in which a sample of tissue Is taken from the placenta. According to ACOG, it can be done at 10-13 weeks into the pregnancy, earlier than amniocentesis. It does, however, have a higher risk of miscarriage than amniocentesis. The Centers for Disease Prevention and Control states the risk of miscarriage at 0.5-1 percent for CVS and 0.25-0.5 percent for amniocentesis. These risks may be overstated, according to a 2019 article in Ultrasound Obstetrics & Gynecology, which reviewed 19 studies and found procedure-related risks was 0.12 percent or lower when only women with similar profiles were compared.
Online DNA Testing
As scientific understanding of genetics has increased, so have the number of mutations for which tests have been developed. In recent years, private companies, such as 23andMe and AncestryHealth, have begun marketing genetic health tests to consumers.
“For the most part, knowledge is power. But it can cause anxiety,” Dr. Lupton said.
Testing sold by private companies is less complete than those obtained through a doctor’s office, he said.
23andMe tests for 29 variants of the CFTR gene that causes cystic fibrosis, he said, while his department uses Quest Diagnostics to test for 161. Quest also offers a broader test that can look for about 1,000 variants associated with 98 percent of cystic fibrosis cases. More than 1,700 variants of this gene have been discovered, according to the CF Foundation.
The number of mutations that may cause cystic fibrosis illustrates the complexity of genetic disease. And genetics alone isn’t responsible for some disease.
“A lot of these disorders are multifactorial – both genetic and environmental,” Dr. Lupton said.
If a woman is pregnant, “any abnormal genetic testing results would prompt us to refer the patient to MFM (maternal fetal medicine). At Cape Cod Hospital, we refer to Dr. Tamara Takoudes who meets with high-risk pregnant patients every week for consultations,” he said.
“Outside of pregnancy, we typically refer patients to a genetic counselor at Cuda Women's Health if they are at risk of any type of hereditary cancer disorder based on personal and family history (such as hereditary breast and ovarian syndrome, Lynch syndrome, etc.).”
Parents-to-be or any adult can start investigating their risk of some common inherited diseases by answering this questionnaire on Cape Cod Healthcare’s website: https://www.hereditarycancerquiz.com/cchealth
Insurance companies will pay for most genetic tests, Dr. Lupton said.
“Most carrier screenings should be covered, if indicated,” he said. “Usually just requires physician to sign off.”