A 22-year-old woman at 14 weeks gestation comes to the physician for a prenatal visit. She reports feeling well with the exception of some mild fatigue. Her pregnancy has been uncomplicated to date. On physical examination, the patient's abdomen appears larger than would be expected at 14 weeks. An obstetrical ultrasound reveals twins, a male and a female. Which of the following describes the most likely type of twin placentation in this patient?

Question

A 22-year-old woman at 14 weeks gestation comes to the physician for a prenatal visit.  She reports feeling well with the exception of some mild fatigue.  Her pregnancy has been uncomplicated to date.  On physical examination, the patient's abdomen appears larger than would be expected at 14 weeks.  An obstetrical ultrasound reveals twins, a male and a female.  Which of the following describes the most likely type of twin placentation in this patient?

Quizplus · Accepted Answer

11ec160b_374d_a7ca_9249_eda9cd7bb5d0_MD0001_00 This patient is pregnant with twins of different sexes which can only occur in dizygotic twins due to the fertilization of 2 oocytes by 2 different sperm. Dizygotic twins are almost always dichorionic/diamniotic (eg, 2 chorions and 2 amnions) but may falsely give the appearance of being monochorionic/monoamniotic if the chorions and amnions fuse due to proximity of implantation sites. In contrast, monozygotic twins develop from division of a single zygote after fertilization of a single oocyte. They are of the same sex, are genetically identical, and are similar in appearance. The type of placentation in monozygotic twins depends on when zygote division occurs during embryonic development. (Choice B) Dichorionic/monoamniotic twins do not exist. Educational objective: Dizygotic twins occur due to fertilization of 2 oocytes by 2 different sperm, can be different sexes, and almost always have 2 chorions and 2 amnions (eg, dichorionic/diamniotic). In contrast, monozygotic twins arise from the fertilization of a single oocyte, are the same sex, and can be dichorionic/diamniotic (days 0-4), monochorionic/diamniotic (days 4-8), monochorionic/monoamniotic (days 8-12), or monochorionic/monoamniotic conjoined twins (> 13 days).

A 22-Year-Old Woman at 14 Weeks Gestation Comes to the Physician