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Prenatal genetic evaluation of the anomalous fetus

Authors
Neeta Vora, MD
Sarah Harris, MS, CGC
Section Editor
Louise Wilkins-Haug, MD, PhD
Deputy Editor
Vanessa A Barss, MD, FACOG

INTRODUCTION

Approximately 3 percent of live births are affected by a major structural malformation [1]. With advances in prenatal ultrasound, many of these anomalies are now identified before birth. The etiology is diverse and includes environmental factors, genetic factors, or a combination of both.

As the landscape of genetic testing rapidly evolves, clinicians are often left with many questions about the most appropriate testing methods to use for their patients. This topic will provide a reasonable approach to the genetic evaluation of an anomalous fetus. Postnatal evaluation of the anomalous infant is reviewed separately. (See "Birth defects: Approach to evaluation".)

FREQUENCY OF CHROMOSOME ABNORMALITIES IN ANOMALOUS FETUSES

The finding of a fetal structural anomaly increases the possibility of a chromosome abnormality or genetic molecular defect and should prompt further evaluation into genetic etiologies. The frequency of a chromosome abnormality depends on the specific anomaly, the number of anomalies, and the combination of anomalies identified [2]. In several retrospective series of prenatally detected anomalies on ultrasound that prompted genetic studies, an isolated fetal anomaly was associated with fetal chromosome abnormalities in 2 to 18 percent of cases; multiple anomalies were associated with a fetal chromosome abnormality in 13 to 35 percent of cases [2-7].

DIAGNOSTIC TESTING

Our approach — We offer a diagnostic procedure to patients with structural fetal abnormalities on ultrasound examination (algorithm 1) [8]. The goal is to determine whether there is a genetic etiology of the abnormalities that would enable well-informed counseling about prognosis, reproductive options, obstetric and pediatric management, and recurrence risks.

The decision to undergo invasive testing is personal and must be based on the individual patient's values and goals. Pretest counseling by a provider familiar with the suspected fetal diagnoses and with genetic testing options is necessary for patients to make informed decisions. Alternatives to prenatal diagnostic testing include prenatal screening and postnatal diagnostic testing.

                 
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Literature review current through: Oct 2017. | This topic last updated: Nov 13, 2017.
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