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LEARNING OBJECTIVES

  1. Describe prenatal testing options.

  2. Describe the difference between screening methods and invasive diagnostic techniques.

  3. Discuss the 2016 ACOG recommendations for offering prenatal diagnostic testing.

  4. Recall literature regarding pregnancy outcomes associated with prenatal fetal testing.

INTRODUCTION

Prenatal diagnosis is a broad term and involves the detection of chromosomal or structural fetal abnormalities before birth. This has become an integral part of prenatal care offered to all pregnant women. It is important to understand that diagnosing a chromosomal or structural abnormality prior to delivery is a multistep process. Typically, this involves identification of risk factors, discussion of first and second-trimester screening tests, targeted ultrasound, genetic counseling, discussion of the option of diagnostic tests, and patient follow-up.

Patient Case (Part 1)

A 36-year-old woman presents to her obstetrician at 12 weeks of gestation to ask questions and discuss concerns about the health of her baby.

HPI: She is concerned because her cousin recently delivered a baby with Down syndrome. The patient is counseled regarding different options for screening and elects to undergo first-trimester screening.

Physical Examination: Within normal limits.

Medications: Prenatal vitamin with omega 3.

Allergies: Codeine.

Lab Results: Serum analytes were sent and the results return 1 week later. They show that her risk of having a child with Down syndrome is 1 in 89.

Diagnostics: An ultrasound is performed that revealed a single intrauterine gestation with a thickened nuchal translucency (NT).

Patient Assessment: The assessment of this patient is that she is of advanced maternal age (AMA) with a positive screening test for Down syndrome, as well as an ultrasound marker associated with an increased risk of Down syndrome.

SCREENING AND DIAGNOSTIC TESTS

Screening tests have become increasingly common in obstetrics. Screening involves the use of tests, examinations, or procedures to assist in the presumptive diagnosis of patients with unrecognized disease. Screening tests are used to help identify individuals who are more likely to have disease, as well as those who are less likely to have disease. These tests are usually applied to a low-risk population. Individuals identified by a positive screening test or an abnormal screening test are recommended to undergo further diagnostic testing to determine whether they truly have the disease or the diagnosis being investigated.1

There are several properties that are important principles of a good screening test. The disease or medical condition should be a serious medical problem. The natural history of the disease should be known, and there should be an early period or stage that may be identified through testing. The test should be able to be applied to a large low risk population, and it should be suitable and effective. Standard policies and procedures should be in place to determine which patients should be referred for further diagnostic testing. Access to health care facilities for further diagnostic testing and treatment should be available. The ...

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