The three regions of the decidua include which of the following? Select all that apply

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.

Fertilization is the process whereby a single sperm penetrates the oocyte cytoplasm, initiating the fusion of genetic material. This event results in the formation of a diploid zygote through the fusion of the male and female pronuclei. Fertilization triggers the completion of the oocyte's second meiotic division and initiates the first mitotic divisions. The zygote contains 46 chromosomes (23 pairs), restoring the diploid number essential for normal embryogenesis.

Rationale for correct answers

C. After sperm entry, the male and female pronuclei migrate towards each other and fuse, creating a single diploid nucleus within the zygote. This fusion marks the true completion of fertilization and the genetic unification necessary for embryonic development.

Rationale for incorrect answers

A. The formation of a blastocyst, containing an inner cell mass and trophoblast, occurs several days post-fertilization during the blastocyst stage, not immediately upon sperm-oocyte fusion.

B. Differentiation of the morula into an embryo occurs after several rounds of cleavage and compaction, occurring days after fertilization, thus not at the immediate completion of fertilization.

D. Rapid mitotic divisions producing blastomeres begin after fertilization but represent cleavage stages rather than the completion event of fertilization itself, which is specifically defined by pronuclear fusion.

Take home points

• Fertilization completion is defined by the fusion of male and female pronuclei forming a diploid zygote.
• The zygote contains 46 chromosomes, restoring diploidy essential for normal development.
• Subsequent events such as cleavage and blastocyst formation occur days after fertilization.
• Early embryogenesis depends on successful pronuclear fusion to initiate mitotic divisions.