What are the next steps for a primigravida (primi) with a Down syndrome risk of 1:391?

Management of Primigravida with Down Syndrome Risk of 1:391

This patient has a screen-negative result and does not require invasive diagnostic testing, but should receive genetic counseling to understand her options, including the availability of diagnostic testing if she desires definitive information about fetal chromosomal status. 1

Understanding the Risk Assessment

A Down syndrome risk of 1:391 falls below the typical screen-positive threshold used in most screening programs. The standard cutoff for screen-positive results is generally 1:190 to 1:300, meaning this patient's risk is in the screen-negative range. 1, 2

• Screen-negative results indicate the pregnancy is at lower risk for Down syndrome compared to the cutoff threshold used by the laboratory 1
• The most common outcome associated with any elevated Down syndrome risk estimate (even when screen-positive) is delivery of an unaffected infant 1

Recommended Next Steps

Counseling and Patient Autonomy

All pregnant women, regardless of screening results or maternal age, should have the option of invasive diagnostic testing (CVS or amniocentesis) after appropriate counseling about risks and benefits. 1

• The American College of Obstetricians and Gynecologists recommends that diagnostic testing be made available if requested, respecting patient autonomy 1
• Women who do not want further information about chromosomal status should not be required to undergo additional testing 1

Genetic Counseling Considerations

Genetic counseling should be offered to discuss:

• The meaning of the risk estimate and how it compares to age-related baseline risk 1
• Options for diagnostic testing including CVS (10-13 weeks) or amniocentesis (≥15 weeks) 1
• Procedure-related risks: amniocentesis carries approximately 1 in 300-600 risk of pregnancy loss, with some studies suggesting no significant increase over background miscarriage risk 1
• Alternative screening options if still in appropriate gestational window 1

When Genetic Counseling is Particularly Important

Referral for genetic counseling is especially reasonable when there is:

• Family history of multiple individuals with Down syndrome, which may indicate a familial translocation 1
• Patient anxiety or desire for more detailed information about screening versus diagnostic testing 1

Important Caveats

Screen-Negative Does Not Mean Zero Risk

• A screen-negative result reduces but does not eliminate the possibility of Down syndrome 1
• The detection rate of first-trimester combined screening (NT + PAPP-A + hCG) is approximately 82-86% with a 5% false-positive rate, meaning some affected pregnancies will have reassuring screening results 1

Patient Preference is Paramount

• Some women may still choose diagnostic testing despite screen-negative results for definitive reassurance 1
• A nondirective approach should be used when presenting options 3
• Women should receive detailed information about screening limitations and diagnostic testing options to make informed decisions 1

Documentation

• Screen-negative results can be transmitted by mail, courier, or electronic transmission 1
• The report should clearly indicate the result is screen-negative, the risk cutoff level used, and the patient-specific risk 1