A 40-year-old woman, gravida 2 para 1, comes to the office for her initial prenatal visit. She is at 10 weeks gestation based on her last menstrual period. The patient has no concerns today and feels well. She had light vaginal bleeding 6 weeks ago, but none since then. Her first pregnancy ended in a term vaginal delivery. The patient has no chronic medical conditions or prior surgeries and takes no daily medications. She does not use tobacco, alcohol, or illicit drugs. Blood pressure is 118/64 mm Hg and pulse is 82/min. BMI is 22 kg/m². Physical examination is unremarkable. Ultrasound reveals an intrauterine fetal pole at 10 weeks gestation with fetal heart rate at 160/min. In addition to routine prenatal laboratory testing, which of the following tests is recommended for this patient?
Cell-free fetal DNA testing | |
Indications |
|
Applications |
|
The initial prenatal visit uses a combination of maternal history and prenatal testing to identify patients at risk for obstetric complications. Prenatal testing can be routine (eg, HIV screen, maternal blood typing) or risk based.
Women age ≥35 (ie, advanced maternal age) are at increased risk of fetal aneuploidy and are offered cell-free fetal DNA testing (cffDNA) of maternal plasma. Other indications include abnormal maternal serum screening test results (eg, quadruple screen) or an abnormal ultrasound. Noninvasive cffDNA testing can be performed at ≥10 weeks gestation and has a high sensitivity and specificity for detecting trisomy 21 (Down syndrome), trisomy 18 (Edward syndrome), and trisomy 13 (Patau syndrome). It can also identify the fetal sex and some sex chromosome disorders.
Normal results are reassuring and typically require no additional evaluation. Abnormal results are confirmed by fetal karyotyping via first-trimester chorionic villus sampling or second-trimester amniocentesis.
(Choice B) Cytomegalovirus antibody testing is indicated in patients with a suspected congenital infection (eg, fetal growth restriction, periventricular calcifications); however, routine screening is not performed.
(Choice C) Screening for inherited thrombophilias (eg, antithrombin deficiency) is not recommended in patients without risk factors such as family history or prior venous thromboembolism.
(Choice D) Quantitative β-hCG levels are indicated in patients with a pregnancy of unknown location because abnormal levels may indicate an ectopic pregnancy; β-hCG levels have no clinical value once an intrauterine pregnancy is confirmed on ultrasound, as in this patient.
(Choice E) Although prenatal screening for Chlamydia trachomatis and Neisseria gonorrhoeae is routine, Trichomonas vaginalis nucleic acid amplification testing is indicated only in symptomatic patients or those with risk factors (eg, HIV).
Educational objective:
Cell-free fetal DNA testing is a noninvasive and highly sensitive and specific screening test for fetal aneuploidy. It is performed at ≥10 weeks gestation, and abnormal results are confirmed by chorionic villus sampling or amniocentesis.