WBR0513

Author	[[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Reproductive
Prompt	[[Prompt::A couple, trying to conceive a child for 5 years, visits the in-vitro fertilization (IVF) center. The physician informs the family that during IVF, the embyro is directly implanted in the uterus. In a normal pregnancy, at which day post-fertilization does an embryo undergoes implantation in the uterus?]]
Answer A	AnswerA::Day 2
Answer A Explanation	AnswerAExp::On day 2, the zygote is still within the fallopian tubes and has not descended to the level of the endometrium.
Answer B	AnswerB::Day 4
Answer B Explanation	AnswerBExp::On day 4, the morula is still within the fallopian tubes and has not descended to the level of the endometrium.
Answer C	AnswerC::Day 6
Answer C Explanation	AnswerCExp::On day 6, the blastocyst is in the endometrium and implantation begins.
Answer D	AnswerD::Day 10
Answer D Explanation	AnswerDExp::By day 10, implantation already started and hCG is being secreted.
Answer E	AnswerE::Day 12
Answer E Explanation	AnswerEExp::On day 12, implantation already started and hCG is being secreted.
Right Answer	RightAnswer::C
Explanation	[[Explanation::During a normal pregnancy, fertilization occurs at day 0. The fertilization process typically occurs in the ampullary-ischmic junction of the fallopian tubes. Soon following fertilization, the oocyte proceeds with the meiosis II that had been arrested after ovulation. The fertilized egg continues to descend along the fallopian tube as mitosis of the embryo progressively occurs, becoming a morula on day 3 and a blastocyst on day 5. On day 6, the blastocyst reaches the endometrium and implantation is initiated. The pregnancy becomes detectable by serum and urinary concentrations of hCG within 10-14 days post-fertilization. Educational Objective: Typically, blastocyst implantation occurs on day 6 post-fertilization. References: First Aid 2014 page 552]]
Approved	Approved::Yes
Keyword	WBRKeyword::day 6, WBRKeyword::implantation, WBRKeyword::blastocyst, WBRKeyword::morula, WBRKeyword::secretion, WBRKeyword::hCG, WBRKeyword::zygote, WBRKeyword::fertilization, WBRKeyword::egg, WBRKeyword::oocyte, WBRKeyword::sperm, WBRKeyword::endometrium, WBRKeyword::uterus, WBRKeyword::IVF, WBRKeyword::pregnancy, WBRKeyword::meiosis, WBRKeyword::mitosis, WBRKeyword::reproduction
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::