ACOG has published two committee opinions on carrier screening. Committee Opinion 691 reviews the recommendations based on disorders. Committee Opinion 690 addresses the issues related to use of screening strategies such as expanded gene panel testing.
Spinal Muscular Atrophy (SMA) has joined cystic fibrosis (CF) as a recommendation for all women who are pregnant or considering pregnancy
Test all patients for CBC and RBC indices as part of antepartum care (ideally preconception)
Add Hgb electrophoresis if
Increased risk based on ethnicity: African, Middle Eastern, Southeast Asian, West Indian and Mediterranean ancestry
MCV is less than 80 fL with normal iron studies
Ashkenazi Jewish Testing (central and Eastern Europe descent)
Additional tests to ‘consider’ has been expanded to the following
Usher syndrome, Familial hyperinsulinism, Joubert and Maple syrup urine disease in addition to Bloom/Gaucher/Fanconi anemia/ML4/Neimann-Pick disease
Tay Sachs Disease
In addition to Ashkenazi Jews, offer if either partner is French-Canadian descent or Cajun
Screening can be performed using DNA-based testing (mutation analysis) or hexosaminidase enzyme in serum or leuckocytes (leukocyte only with oral contraceptives)
Enzyme testing picks up approximately 98% of carriers regardless of ethnicity
Mutation analysis is highly effective in at risk populations – detection rate is limited in other populations
Committee Opinion 690 reviews expanded carrier screening, including a discussion on counseling and what disorders should be included | Important summary statements include the following
Ethnic-specific, panethnic, and expanded carrier screening are acceptable strategies for prepregnancy and prenatal carrier screening. Each obstetrician–gynecologist or other health care provider or practice should establish a standard approach that is consistently offered to and discussed with each patient, ideally before pregnancy. After counseling, a patient may decline any or all carrier screening.
Expanded carrier screening does not replace previous risk-based screening recommendations. If obstetrician–gynecologists or other health care providers do not offer expanded carrier screening in their practice, screening recommendations for individual disorders should follow guidelines for carrier screening as outlined in Committee Opinion No. 691, Carrier Screening for Genetic Conditions.
Note: ACMG has published a document on preconception and prenatal carrier screening that includes a tiered approach to the selection of disorders | For the summary and links see ‘Related ObG Topics’ below)
ACOG and Universal Screening for Cystic Fibrosis – What You Need to Know
Genetic screening for Cystic Fibrosis (CF) has been recommended by ACOG and ACMG for over a decade.
Offer CF screening to all women of reproductive age, not just those in higher risk groups
Document previous CF screening results
Genetic testing does not need to be repeated in subsequent pregnancies if already on record
Expanded mutation panels beyond the ‘ACMG 23’ can be considered to increase sensitivity
DNA sequencing of the CFTR gene is not considered ‘appropriate’ for routine carrier screening and should be reserved for particular circumstances in conjunction with genetic counseling (see below in key points)
Refer for genetic counseling if both partners are CF carriers
CF is an autosomal recessive disorder and if both partners are affected, the risk to offspring is ¼ or 25%
Initially, prenatal screening for CF was limited to women from high risk groups, non-Hispanic whites and those of Ashkenazi Jewish background. However, as it becomes more difficult to identify specific racial groups and ethnicities, ACOG guidance is clear that all women of reproductive age should be screened to determine their carrier status. There are several genetic tests currently available that can sequence the entire CFTR gene, providing a clinical report for hundreds of CF disease causing mutations. While Committee Opinion 691 still mentions the original ACMG 23 mutation panel, expanded mutation panel analysis can be considered to help improve test sensitivity particularly among non-Caucasians.
Full gene sequencing of the CFTR gene should be reserved for patients who meet the following criteria:
Personal history of CF
Family history of CF
Males with CBAVD
Newborns with positive newborn screening results when mutation panel testing is negative
Newborn screening for CF in newborns does not replace maternal screening
A negative newborn screen for CF cannot identify parental carriers
Second Trimester Echogenic Bowel: Important Ultrasound Finding with Varied Causes and Some Serious Implications
Fetal bowel can sometimes appear bright on prenatal ultrasound depending on the transducer used and machine settings. However, echogenic bowel in the fetus is not a significant finding unless the bowel appears as bright as bone (the brightness of the iliac wing can be used a reference). If the ultrasound report does confirm echogenic fetal bowel, further management should include
No previous aneuploidy screening
NIPS or quad screening
Negative aneuploidy screening
No further aneuploidy evaluation
Offer cystic fibrosis screening if not yet performed in current or prior pregnancy
Evaluate for cytomegalovirus (CMV) infection with IgG and IgM titers
Follow-up fetal growth scan in the third trimester to evaluate for growth restriction
If aneuploidy screening is positive, offer confirmatory diagnostic testing, referral for high-risk OB consultation and genetic counseling
Fetal echogenic bowel is present in up to 1.8% of second trimester ultrasound exams. It can be due to congenital cytomegalovirus infection, cystic fibrosis, intra-amniotic bleeding, fetal growth restriction, aneuploidy or gastrointestinal obstruction. Therefore, further work-up is warranted.
Echogenic bowel is associated with aneuploidy (3 to 5%), the most common is Down syndrome (Trisomy 21)
If all identifiable causes are ruled out, fetal growth should be evaluated, as there is an association with fetal growth restriction
When isolated, normal fetal outcomes are likely. Pediatrics should be informed of the prenatal findings and work-up
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