What prenatal genetic screens do medical societies recommend and why?

When you become an expecting parent, you also begin a close collaboration with the healthcare practitioner who will be guiding you through this phase of your life. That person could be an obstetrician, a family practice doctor, a nurse practitioner, a maternal-fetal medicine doctor, a midwife, or a doula. No matter who your practitioner is, they often rely on their own sources of guidance: medical societies like the American College of Obstetricians and Gynecologists (ACOG).

ACOG helps providers by making recommendations that it believes will support the best outcomes possible, including what tests and screens to perform during pregnancy. Let’s explore the types of prenatal genetic screens recommended by medical societies like ACOG and learn why they are important.

Carrier screening

Carrier screening is typically done before or during pregnancy to determine if parents carry a genetic change, sometimes called a mutation, for a serious, inherited genetic condition. There are some conditions that are passed on to male babies only if the maternal parent carries the genetic change. For most other conditions, both parents have to be carriers of the same genetic condition. When that happens, there is a 25% chance their baby could be affected by the disorder. Carrier screening can assess the risk for a variety of conditions, including:

• Cystic fibrosis: A condition that affects the lungs and digestive system.
• Spinal muscular atrophy (SMA): A condition that affects muscles and movement.
• Fragile X: A condition that affects learning and development.

An ACOG committee has recommended that “all patients who are considering pregnancy or are already pregnant…should be offered carrier screening for cystic fibrosis and spinal muscular atrophy, as well as a complete blood count and screening for thalassemias and hemoglobinopathies.”¹ Other societies have recommended an even longer list of conditions that should be included in the screening process. We suggest you speak to your provider about the conditions they typically assess.

Prenatal cell-free DNA (cfDNA) screening

Prenatal cfDNA screening, also known as non-invasive prenatal testing (NIPT), analyzes small fragments of the baby’s DNA circulating in the mother’s blood. Unlike carrier screening which looks for gene changes, cfDNA screening is looking for chromosomal changes.

People usually have 23 pairs of chromosomes, one of each from each parent. CfDNA screening is looking for times when a baby may have too few (one instead of two) or too many (three instead of two) chromosomes, or a small piece of the chromosome is missing (microdeletion) or in excess (microduplication) .

This test can be done as early as eight weeks into the pregnancy and can screen for:

• Common trisomies: Down (trisomy 21), Edwards (trisomy 18) or Patau (trisomy 13) syndromes: Conditions caused by the presence of an extra chromosome.
• Sex chromosome aneuploidies: Conditions involving missing or extra sex chromosomes, such as Turner syndrome or Klinefelter syndrome.
• Microdeletions: Conditions caused by small missing pieces of a chromosome, such as 22q, where the change can cause varying degrees of learning disabilities and other health concerns including heart conditions.

ACOG recommends cfDNA screening for all pregnant people, regardless of age or risk factors.²  Prenatal cfDNA screens offer a high degree of accuracy and are non-invasive; all that is required is a blood sample from the pregnant person.

How medical societies choose what conditions to recommend screening for

Medical societies also recommend that diseases included in screens should meet several of the following criteria:

Severity: The condition should have significant health implications for the baby.

Frequency: The condition should be relatively common in the population.

Detectability: Reliable and accurate tests should be available to detect the condition.

Intervention: There should be treatments or interventions available that can improve outcomes for the baby.²

In following recommendations by these medical experts, you can gain access to relevant, actionable information. This empowers you to make informed decisions and take further actions, like getting diagnostic testing or researching medical facilities and specialists. And since most screens will present you with a low-risk result, peace of mind is likely to be the outcome.

REFERENCES

1. American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics; Committee on Genetics; Society for Maternal-Fetal Medicine. Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226. Obstet Gynecol. 2020;136(4):e48-e69. doi:10.1097/AOG.0000000000004084.
2. Carrier screening in the age of genomic medicine. Committee Opinion No. 690. American College of Obstetricians and Gynecologists. Obstet Gynecol 2017;129:e35–40.