Conjoined twins are formed at which point of gestation?

Correct Answer: C

Rationale: Conjoined twins are formed at about 13 to 15 days after conception when the embryonic disc undergoes incomplete splitting. At this stage, the cells have already differentiated into different layers, making separation challenging. Immediately after fertilization (choice A) is too early for conjoined twins to form. At the time of implantation (choice B) is when the blastocyst implants into the uterine wall, but conjoined twins are not formed at this point. In the blastocyst stage (choice D), the cells are still in the process of organizing and have not yet differentiated into distinct layers. Therefore, choice C is the correct answer as it aligns with the timing of conjoined twin formation during embryonic development.

Correct Answer: A

Rationale: The correct answer is A: IgG. IgG is the only immunoglobulin that can cross the placenta due to its small size and ability to bind to the neonatal Fc receptor. This transfer provides passive immunity to the fetus, protecting it from infections. IgA primarily functions in mucosal immunity and is found in secretions like breast milk. IgM is too large to cross the placenta and is mainly produced in response to acute infections. IgD is primarily found on the surface of B cells and functions in the activation of these cells.

Correct Answer: C

Rationale: The correct answer is C (20 weeks) because quickening, the first perception of fetal movement by the mother, typically occurs around this time. At 20 weeks, the fetus is large enough for its movements to be noticeable to the mother. Before 20 weeks, the fetus is too small and the movements are not strong enough to be felt. Choices A, B, and D are incorrect because they are too early in the pregnancy for the mother to feel fetal movement. By 20 weeks, the fetus has developed enough for the mother to perceive its movements, making option C the correct answer.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.