Which of the following statements accurately describes the role of the amnion at 12 weeks gestation?
“The amnion produces hormones to maintain your pregnancy.”
“The amnion forms a protective sac filled with amniotic fluid.”
“The amnion facilitates nutrient exchange with the placenta.”
“The amnion develops into the umbilical cord.”
The Correct Answer is B
The amnion is a thin, transparent membrane that forms the innermost layer of the fetal membranes, creating a protective sac filled with amniotic fluid. By 12 weeks gestation, the amnion has expanded to enclose the fetus completely, providing a cushioning environment, temperature regulation, and protection against infection and mechanical injury. Amniotic fluid volume normally ranges from 50 ml at 12 weeks to approximately 800 ml at term. The amnion does not produce hormones or directly facilitate nutrient exchange, which is the role of the placenta.
Rationale for correct answers
B. The amnion forms a protective sac that contains amniotic fluid, which cushions the fetus and permits movement. At 12 weeks, this sac is fully formed, surrounding the embryo/fetus with fluid essential for normal development and mechanical protection.
Rationale for incorrect answers
A. The amnion does not produce hormones; hormone production to maintain pregnancy is primarily by the trophoblast and placenta, including human chorionic gonadotropin and progesterone.
C. Nutrient exchange occurs at the placenta via chorionic villi, not the amnion, which acts as a barrier and container for amniotic fluid but does not participate in exchange functions.
D. The umbilical cord develops from the connecting stalk and allantois, not from the amnion. The amnion lines the amniotic cavity but does not differentiate into the umbilical cord.
Take home points
- The amnion forms a protective sac filled with amniotic fluid by 12 weeks gestation.
- Amniotic fluid cushions and protects the fetus, volume increases from 50 ml at 12 weeks to 800 ml at term.
- Hormone production for pregnancy maintenance occurs in the placenta, not the amnion.
- Nutrient and gas exchange occurs through the placenta, not the amnion.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Oligohydramnios is defined as a decreased amount of amniotic fluid, usually less than 500 mL in the third trimester or an amniotic fluid index (AFI) less than 5 cm. It results from decreased fetal urine production or increased fluid loss and is associated with fetal renal anomalies, rupture of membranes, or placental insufficiency. The amniotic fluid plays critical roles in lung development, cushioning, and movement. Prolonged oligohydramnios compromises lung growth leading to pulmonary hypoplasia, a condition where the lungs are underdeveloped, impairing neonatal respiratory function.
Rationale for correct answers
C. Pulmonary hypoplasia occurs because amniotic fluid is essential for normal lung development by maintaining fluid pressure and allowing lung expansion in utero. Prolonged oligohydramnios reduces this fluid, resulting in underdeveloped lungs with fewer alveoli and decreased pulmonary vasculature, causing respiratory insufficiency at birth.
Rationale for incorrect answers
A. Macrosomia, defined as fetal weight above 4000 grams, is unrelated to oligohydramnios and more often linked to maternal diabetes or genetic factors. Reduced amniotic fluid does not cause fetal overgrowth.
B. Shoulder dystocia is an obstetric complication caused by fetal size disproportion, often macrosomia, and is not directly caused by oligohydramnios.
D. Hyperbilirubinemia results from increased red blood cell breakdown or impaired conjugation, unrelated to amniotic fluid volume. Oligohydramnios does not predispose to bilirubin metabolism disorders.
Take home points
- Oligohydramnios is characterized by AFI less than 5 cm or fluid volume under 500 mL in the third trimester.
- Prolonged oligohydramnios leads to pulmonary hypoplasia due to impaired fetal lung development.
- Macrosomia and shoulder dystocia are unrelated to oligohydramnios but linked to fetal size.
- Hyperbilirubinemia is unrelated to amniotic fluid volume but linked to red blood cell metabolism.
Correct Answer is C
Explanation
Amniocentesis is an invasive prenatal diagnostic procedure primarily used to sample amniotic fluid for chromosomal, genetic, and fetal lung maturity assessments. Typically performed between 15 and 20 weeks’ gestation, it involves transabdominal insertion of a needle under ultrasound guidance to withdraw 15–20 mL of fluid containing fetal cells. This fluid contains fetal DNA, proteins like lecithin and sphingomyelin, which are used to assess lung maturity, with a lecithin/sphingomyelin (L/S) ratio above 2.0 indicating mature lungs. It also helps diagnose genetic disorders and neural tube defects.
Rationale for correct answers
C. Amniocentesis samples amniotic fluid to analyze fetal cells for chromosomal abnormalities (e.g., trisomy 21), genetic mutations, and biochemical markers for lung maturity such as the L/S ratio, providing critical information for fetal health assessment.
Rationale for incorrect answers
A. Measuring fundal height is a non-invasive clinical method to estimate fetal growth and weight, unrelated to amniocentesis.
B. Doppler ultrasound assesses uteroplacental blood flow and fetal circulation but does not involve sampling amniotic fluid.
D. Fetal heart tones are detected by Doppler or fetoscope, especially in early pregnancy, and are not confirmed by amniocentesis.
Take home points
- Amniocentesis is used to sample amniotic fluid for genetic and lung maturity testing.
- It provides critical prenatal diagnostic information on chromosomal abnormalities and fetal well-being.
- Fundal height measurement and Doppler ultrasound serve different diagnostic roles unrelated to amniocentesis.
- Fetal heart tones are confirmed by non-invasive methods, not amniocentesis.
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