FETAL MEDICINE

Fetal Medicine

Fetal Medicine

Introduction

Pregnant women of all ages should be offered screening and invasive diagnostic testing for chromosomal abnormalities before 20 weeks' gestation. New developments in screening methods have increased the number of options for patients. Diagnostic options include chorionic villus sampling in the first trimester and amniocentesis in the second trimester. Screening options in the first trimester include nuchal translucency testing in combination with measurement of pregnancy-associated plasma protein A and human chorionic gonadotropin. Nuchal translucency testing alone is not as effective. Screening options in the second trimester include serum screening using triple or quadruple screening, and ultrasonography. Patients may also choose a combination of first- and second-trimester screening in an integrated, stepwise sequential, or contingent sequential fashion. These options include an analysis of pregnancy-associated plasma protein A, with or without nuchal translucency testing, in combination with quadruple screening. An integrated test with nuchal translucency testing is the most effective method for women who present in the first trimester. If nuchal translucency testing is unavailable, the maternal serum-integrated test is safest and most effective. For women who do not present until the second trimester, the quadruple screen is recommended. Comprehensive counseling should be available to all pregnant women. Specific screening tests will depend on availability of the procedure and patient preference.

Discussion

Screening for fetal chromosomal abnormalities is an essential part of antenatal care. Historically, maternal age was the determinant of risk. Women older than 35 years at the time of delivery were offered genetic counseling and amniocentesis because of procedure-related loss rates. However, only 20 percent of infants with Down syndrome (trisomy 21) are born to women older than 35 years.1 With the advent of maternal serum alpha-fetoprotein (AFP) testing in the mid-1980s, women younger than 35 years had an option for antenatal diagnosis. In the past two decades, additional tests have been shown to increase the detection rate of chromosomal abnormalities while maintaining a low false-positive rate. This gives pregnant women of all ages the opportunity to undergo screening or invasive diagnostic testing before 20 weeks' gestation. Table 1 provides a glossary of terms related to fetal screening.

Sort: Key Recommendations For Practice

Clinical recommendations

Evidence rating

Comment

Pregnant women should be offered screening and invasive diagnostic testing regardless of age.

B

Limited or inconsistent evidence

Combined testing is recommended for first-trimester screening.

A

Evidence-based practice guidelines

Quadruple screening is recommended for second-trimester screening.

A

Evidence-based practice guidelines

Women with isolated nuchal thickening or isolated maternal serum AFP (with normal ultrasonography and normal karyotype) should be followed closely because they are at increased risk of poor pregnancy outcomes.

B

Limited or inconsistent evidence

Combined first- and second-trimester screening offers superior detection rates while maintaining low false-positive rates.

B

Limited or inconsistent evidence

Genetics counseling and chorionic villus sampling or amniocentesis should be offered to all women with elevated risk, as determined by serum screening.

A

Evidence-based practice guidelines

Women who pursue first-trimester screening alone should be offered maternal serum AFP testing in the second trimester to screen for neural tube defects.

A

Evidence-based practice guideline

Nuchal translucency testing and serum screening can be performed in multiple gestations, but they are less sensitive than first-trimester ...