Which of the following should the nurse identify as the correct number of vessels in the umbilical cord?

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.

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.