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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{Rim}}  {{Alison}}
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Physiology
|MainCategory=Physiology
Line 20: Line 20:
|MainCategory=Physiology
|MainCategory=Physiology
|SubCategory=Reproductive
|SubCategory=Reproductive
|Prompt=A 28 year old pregnant woman presents to her gynecologist's office for routine pregnancy visit. In the office, the gynecologist performs a pregnancy ultrasound. He informs the patient that she has twins. The physician then explains to the patient that most probably the cleavage of the fertilized egg occurred between day 4 and day 8 post-fertilization. Which of the following findings on ultrasound is most likely present in this patient?
|Prompt=A pregnant 28-year-old female presents to her gynecologist's office for a routine pregnancy visit. In the office, the gynecologist performs a pregnancy ultrasound. He informs the patient that she has twins. Then he explains to the patient that the cleavage of the fertilized egg likely occurred between day 4 and day 8 post-fertilization. Which of the following ultrasound findings is most likely present in this patient?
|Explanation=While dizygotic twins always form from 2 separately fertilized eggs, monozygotic twins form from 1 fertilized egg that later splits into 2 zygotes very early during pregnancy. The time post-fertilization by which the fertilized egg cleaves is very important for determining the number of chorions and amnions.  
|Explanation=While dizygotic twins always form from 2 separately fertilized eggs, monozygotic twins form from 1 fertilized egg that later splits into 2 zygotes during early pregnancy. The time post-fertilization by which the fertilized egg cleaves is important for determining the number of chorions and amnions.  
<br>0-4 days: Dichorionic diamniotic twin pregnancy
<br>0-4 days: Dichorionic diamniotic twin pregnancy
<br>4-8 days: Monochorionic diamniotic twin pregnancy
<br>4-8 days: Monochorionic diamniotic twin pregnancy
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<br> > 13 days: Monochorionic monoamniotic conjoined twin pregnancy
<br> > 13 days: Monochorionic monoamniotic conjoined twin pregnancy


Educational Objective:
|EducationalObjectives= Monochorionic diamniotic twin pregnancy occurs when the fertilized egg cleaves at 4-8 days post-fertilization.
Monochorionic diamniotic twin pregnancy occurs when the fertilized egg cleaves at 4-8 days post-fertilization.
|References= First Aid 2014 page 555
 
|AnswerA=Dichorionic diamniotic twin pregnancy
|AnswerA=Dichorionic diamniotic twin pregnancy
|AnswerAExp=Dichorionic diamniotic twin pregnancy occurs when cleavage takes place between 0-4 days post-fertilization.
|AnswerAExp=Dichorionic diamniotic twin pregnancy occurs when cleavage takes place between 0-4 days post-fertilization.
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|AnswerDExp=Monochorionic monoamniotic twin pregnancy occurs when cleavage takes place between 8-12 days post-fertilization
|AnswerDExp=Monochorionic monoamniotic twin pregnancy occurs when cleavage takes place between 8-12 days post-fertilization
|AnswerE=Monochorionic monoamniotic conjoined twin pregnancy
|AnswerE=Monochorionic monoamniotic conjoined twin pregnancy
|AnswerEExp=Monochorionic monoamniotic conjoined twin pregnancy occurs when cleavage takes place > 13 days post-fertilization. If no cleavage occurs whatsoever, no twinning will take place.
|AnswerEExp=Monochorionic monoamniotic conjoined twin pregnancy occurs when cleavage takes place > 13 days post-fertilization.  
|RightAnswer=B
|RightAnswer=B
|WBRKeyword=monochorionic, dichorionic, monoamniotic, diamniotic, twin, pregnancy, conjoined, twins, twin, fertilization, cleave, cleavage, fertilized, egg, 4, 8, 12, 13, days, post-fertilization, post, zygote, twinning, monozygote, monozygotic
|WBRKeyword=monochorionic, dichorionic, monoamniotic, diamniotic, pregnancy, conjoined twins, fertilization, cleavage, fertilized, post-fertilization, post, zygote, monozygote, monozygotic
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 00:12, 28 October 2020
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Physiology
Sub Category SubCategory::Reproductive
Prompt [[Prompt::A pregnant 28-year-old female presents to her gynecologist's office for a routine pregnancy visit. In the office, the gynecologist performs a pregnancy ultrasound. He informs the patient that she has twins. Then he explains to the patient that the cleavage of the fertilized egg likely occurred between day 4 and day 8 post-fertilization. Which of the following ultrasound findings is most likely present in this patient?]]
Answer A AnswerA::Dichorionic diamniotic twin pregnancy
Answer A Explanation AnswerAExp::Dichorionic diamniotic twin pregnancy occurs when cleavage takes place between 0-4 days post-fertilization.
Answer B AnswerB::Monochorionic diamniotic twin pregnancy
Answer B Explanation AnswerBExp::Monochorionic diamniotic twin pregnancy occurs when cleavage takes place between 4-8 days post-fertilization.
Answer C AnswerC::Dichorionic monoamniotic twin pregnancy
Answer C Explanation AnswerCExp::Dichorionic monoamniotic twin pregnancy is not possible.
Answer D AnswerD::Monochorionic monoamniotic twin pregnancy
Answer D Explanation AnswerDExp::Monochorionic monoamniotic twin pregnancy occurs when cleavage takes place between 8-12 days post-fertilization
Answer E AnswerE::Monochorionic monoamniotic conjoined twin pregnancy
Answer E Explanation [[AnswerEExp::Monochorionic monoamniotic conjoined twin pregnancy occurs when cleavage takes place > 13 days post-fertilization.]]
Right Answer RightAnswer::B
Explanation [[Explanation::While dizygotic twins always form from 2 separately fertilized eggs, monozygotic twins form from 1 fertilized egg that later splits into 2 zygotes during early pregnancy. The time post-fertilization by which the fertilized egg cleaves is important for determining the number of chorions and amnions.


0-4 days: Dichorionic diamniotic twin pregnancy
4-8 days: Monochorionic diamniotic twin pregnancy
8-12 days: Monochorionic monoamniotic twin pregnancy
> 13 days: Monochorionic monoamniotic conjoined twin pregnancy
Educational Objective: Monochorionic diamniotic twin pregnancy occurs when the fertilized egg cleaves at 4-8 days post-fertilization.
References: First Aid 2014 page 555]]

Approved Approved::Yes
Keyword WBRKeyword::monochorionic, WBRKeyword::dichorionic, WBRKeyword::monoamniotic, WBRKeyword::diamniotic, WBRKeyword::pregnancy, WBRKeyword::conjoined twins, WBRKeyword::fertilization, WBRKeyword::cleavage, WBRKeyword::fertilized, WBRKeyword::post-fertilization, WBRKeyword::post, WBRKeyword::zygote, WBRKeyword::monozygote, WBRKeyword::monozygotic
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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