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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{YD}} (Reviewed by Serge Korjian and {{YD}})
|QuestionAuthor= {{YD}} (Reviewed by Serge Korjian and {{YD}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Physiology
|MainCategory=Physiology
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|AnswerEExp=On day 12, implantation has occured and hCG is secreted by the syncytiotrophoblast.
|AnswerEExp=On day 12, implantation has occured and hCG is secreted by the syncytiotrophoblast.
|EducationalObjectives=Blastocyst implantation occurs on day 6 post-fertilization.
|EducationalObjectives=Blastocyst implantation occurs on day 6 post-fertilization.
|References=Cunningham F, Leveno K, Bloom S et al. Williams Obstetrics 24/E. Chapter 5: Implantation and Placental Development. McGraw-Hill Professional; 2014.
|References=Cunningham F, Leveno K, Bloom S et al. Williams Obstetrics 24/E. Chapter 5: Implantation and Placental Development. McGraw-Hill Professional; 2014.<br>
First Aid 2014 page 552
|RightAnswer=C
|RightAnswer=C
|WBRKeyword=Implantation, Blastocyst, Morula, hCG, Zygote, Fertilization, Ampulla, Oocyte, Sperm, IVF
|WBRKeyword=Implantation, Blastocyst, Morula, hCG, Zygote, Fertilization, Ampulla, Oocyte, Sperm, IVF
|Approved=Yes
|Approved=Yes
}}
}}

Latest revision as of 00:49, 28 October 2020

 
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Serge Korjian and Yazan Daaboul, M.D.)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Physiology
Sub Category SubCategory::Reproductive
Prompt [[Prompt::A couple has been trying to conceive a child for 5 years with no success. They decide to explore in-vitro fertilization (IVF) and ask their primary care physician for advice. The physician describes the process explaining that after fertilization the embyro is directly introduced into the uterus. Assuming fertilization occurs at day 0, 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 starts.
Answer D AnswerD::Day 10
Answer D Explanation AnswerDExp::On day 10, implantation has occured and hCG is secreted by the syncytiotrophoblast.
Answer E AnswerE::Day 12
Answer E Explanation AnswerEExp::On day 12, implantation has occured and hCG is secreted by the syncytiotrophoblast.
Right Answer RightAnswer::C
Explanation [[Explanation::During a normal pregnancy, fertilization is considered to occur at day 0. The fertilization process typically occurs in the ampullary-ischmic junction of the fallopian tubes. After fertilization, the oocyte proceeds with meiosis II, which was previously arrested following ovulation. The fertilized egg continues to descend along the fallopian tube as mitotic division of the embryo proceeds and gives rise to the morula on day 3 and the blastocyst on day 5. On day 6, the blastocyst reaches the endometrium, and implantation starts. Soon after implantation takes place, hCG is secreted and pregnancy then becomes detectable by serum and urinary concentrations of hCG within 10-14 days post-fertilization.

Educational Objective: Blastocyst implantation occurs on day 6 post-fertilization.
References: Cunningham F, Leveno K, Bloom S et al. Williams Obstetrics 24/E. Chapter 5: Implantation and Placental Development. McGraw-Hill Professional; 2014.
First Aid 2014 page 552]]

Approved Approved::Yes
Keyword WBRKeyword::Implantation, WBRKeyword::Blastocyst, WBRKeyword::Morula, WBRKeyword::hCG, WBRKeyword::Zygote, WBRKeyword::Fertilization, WBRKeyword::Ampulla, WBRKeyword::Oocyte, WBRKeyword::Sperm, WBRKeyword::IVF
Linked Question Linked::
Order in Linked Questions LinkedOrder::