A fetus with prolonged oligohydramnios is at risk for which complication?
Macrosomia.
Shoulder dystocia.
Pulmonary hypoplasia.
Hyperbilirubinemia.
The Correct Answer is C
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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
The umbilical cord typically contains three vessels: two umbilical arteries and one umbilical vein. The arteries carry deoxygenated blood and waste products from the fetus to the placenta, while the single vein returns oxygenated, nutrient-rich blood from the placenta to the fetus. The normal number of vessels ensures adequate fetal circulation and nutrient exchange. Variations such as a single umbilical artery occur in about 1% of pregnancies and can be associated with congenital anomalies but are not the norm.
Rationale for correct answers
A. The presence of two arteries and one vein is the normal anatomy of the umbilical cord. The two arteries arise from the fetal internal iliac arteries and transport deoxygenated blood to the placenta, while the single vein carries oxygenated blood back to the fetus.
Rationale for incorrect answers
B. One artery and one vein represent an abnormal finding known as a single umbilical artery, which may be associated with congenital anomalies or fetal growth restriction and is not the normal anatomy.
C. Two veins and one artery is not a typical umbilical cord configuration; the umbilical cord normally has only one vein.
D. Three arteries and no veins is anatomically incorrect and incompatible with fetal survival due to lack of oxygenated blood return.
Take home points
- Normal umbilical cord anatomy includes two arteries and one vein.
- Two arteries carry deoxygenated blood from fetus to placenta; one vein returns oxygenated blood.
- Single umbilical artery is an abnormal variant with possible fetal risks.
- Proper vessel number is critical for effective fetal circulation and nutrient exchange.
Correct Answer is B
Explanation
The acrosomal reaction is a crucial event in human fertilization involving the release of hydrolytic enzymes from the sperm’s acrosome. These enzymes allow the sperm to penetrate the zona pellucida, a glycoprotein-rich extracellular matrix surrounding the oocyte. Hyaluronidase and acrosin are the two main enzymes involved. The reaction begins upon binding of the sperm to the ZP3 glycoprotein receptor on the zona pellucida. The acrosomal reaction does not involve genetic fusion but is essential to reach the oocyte membrane. This reaction precedes cortical reaction and oocyte activation.
Rationale for correct answers
B. The acrosomal reaction is defined by the release of hydrolytic enzymes like acrosin and hyaluronidase from the sperm’s acrosomal cap. These enzymes digest the cumulus oophorus and the zona pellucida, allowing sperm to reach the oocyte membrane. This event is molecularly triggered by the binding of sperm to ZP3 receptors on the zona pellucida.
Rationale for incorrect answers
A. Fusion of the male and female pronuclei marks syngamy, which is the final step of fertilization after the sperm has already entered the oocyte. This event occurs after both the acrosomal and cortical reactions and does not define the acrosomal reaction itself.
C. A rapid depolarization of the oocyte membrane is part of the “fast block to polyspermy,” which is associated with the cortical reaction, not the acrosomal reaction. This block prevents multiple sperm from fertilizing the oocyte after one sperm has succeeded, but it happens after the acrosomal reaction is complete.
D. Migration of sperm through the cervical mucus and uterus is a part of sperm transport and capacitation, which occur prior to the acrosomal reaction. This is necessary for the sperm to even reach the site of fertilization, but it is not the defining event of the acrosomal reaction.
Take home points
- The acrosomal reaction is triggered by sperm binding to ZP3 in the zona pellucida.
- Hydrolytic enzymes like acrosin are released to penetrate the zona pellucida.
- The acrosomal reaction is essential for fertilization but occurs before sperm-oocyte membrane fusion.
- It is distinct from the cortical reaction and sperm transport.
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