A 35-year-old woman, gravida 1, para 0, comes to the office to discuss abnormal laboratory results. The patient is at 18 weeks gestation based on her last menstrual period. She drank wine during the first trimester, as she initially did not realize she was pregnant. The patient is otherwise healthy with no medical problems. She takes prenatal vitamins and no other medications. Her immunizations are up-to-date. Results of the quadruple screen performed yesterday are as follows: An ultrasound is scheduled to confirm the patient's gestational age and evaluate for fetal anomalies. Which of the following conditions is the most likely cause of this patient's analyte pattern?

Question

A 35-year-old woman, gravida 1, para 0, comes to the office to discuss abnormal laboratory results.  The patient is at 18 weeks gestation based on her last menstrual period.  She drank wine during the first trimester, as she initially did not realize she was pregnant.  The patient is otherwise healthy with no medical problems.  She takes prenatal vitamins and no other medications.  Her immunizations are up-to-date.  Results of the quadruple screen performed yesterday are as follows:  An ultrasound is scheduled to confirm the patient's gestational age and evaluate for fetal anomalies.  Which of the following conditions is the most likely cause of this patient's analyte pattern?

Quizplus · Accepted Answer

11ec160b_3786_1c67_9249_bd0b64fe254c_MD0001_00 Down syndrome (DS) is the most common chromosomal abnormality and most common genetic cause of intellectual disability. Risk factors include advanced maternal age (age >35) and a parent with a Robertsonian translocation. DS can be screened and diagnosed prenatally. One common option for screening during the second trimester is the quadruple screen at 15-18 weeks gestation. Low maternal serum α-fetoprotein (AFP) and unconjugated estriol levels are associated with DS and correlate with decreased fetal levels (possibly due to suboptimal fetal tissue function). In addition, increased β-hCG and inhibin A are secreted from the placenta, possibly due to compensatory placental hyperfunction. The diagnosis is confirmed by karyotyping fetal cells in the amniotic fluid (amniocentesis). The vast majority of patients with DS have trisomy 21 from meiotic nondisjunction, specifically, failure of chromosome 21 to divide during meiosis. Chromosome 21 nondisjunction occurs during oogenesis and is significantly associated with advanced maternal age; it is not seen in spermatogenesis or in post-zygotic mitotic errors. DS can also result from an unbalanced Robertsonian translocation, during which the entire long arm of one chromosome 21 is translocated to the long arm of an acrocentric chromosome (ie, chromosome 14). These individuals have 46 chromosomes; however, one chromosome 14 is comprised of the long arms of both chromosomes 14 and 21. (Choice A) Abstinence from alcohol is advised for all pregnant women as the amount that can cause teratogenicity is not known. However, the quadruple test is not used to screen for fetal alcohol syndrome. (Choices B, C, and D) Omphalocele and gastroschisis cause increased AFP levels in maternal serum and amniotic fluid. High AFP is also associated with multiple gestation and open neural tube defects (eg, myelomeningocele). Neural tube defects are also associated with increased acetylcholinesterase levels in amniotic fluid. Educational objective: Down syndrome is the most common chromosomal anomaly. It is associated with low levels of maternal serum α-fetoprotein and estriol and increased levels of β-hCG and inhibin A. Elevated α-fetoprotein levels are seen in multiple gestation, open neural tube defects, and abdominal wall defects. __________ References: Influence of second-trimester ultrasound markers for Down syndrome in pregnant women of advanced maternal age. (http://www.ncbi.nlm.nih.gov/pubmed/24795825) The quadruple test for Down syndrome screening in pregnant women of advanced maternal age. (http://www.ncbi.nlm.nih.gov/pubmed/21837420)

A 35-Year-Old Woman, Gravida 1, Para 0, Comes to the Office