WBR0333
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| 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.
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| 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:: |