1. Lecture 8 Ultrasound Evaluation of Multiple Pregnancies Holdorf

2. Important stuff  Zygosity  Monozygotic Twinning  Dizygotic Twinning  Clinical Complications associated with Twin Pregnancy  Maternal Complications  Fetal Complications  Complications of Twin Gestations  Vanishing twin  Twin-twin Transfusion syndrome (TTTS)  Twin embolization syndrome  Conjoined twins  Acardiac twin (Parabiotic twin)

3. But first…Is it twins? Pregnant mothers often suspect that they are carrying more than one baby. Here are some of the most common signs of a twin or multiple pregnancies. Could your patient be having more than one? Check her symptoms against this list.

4. 1. Ultrasound ConfirmationUltrasound Confirmation Seeing is believing... the only way to indisputably confirm a twin or multiple pregnancy is to see it -- via ultrasound. An ultrasound image can indicate without a doubt if there is more than one fetus. Ultimately, no matter what other signs or symptoms your patient has, the only way to know for sure is to have an ultrasound.

5. 2. Doppler Heartbeat Count The Doppler system amplifies fetal heart sounds, usually distinguishable late in the first trimester. An experienced Sonographer can detect more than one heartbeat, indicating a multiple pregnancy. However, the sounds can be misleading; what appears to be a second heartbeat may actually be background noise or, rarely, the mother's own heartbeat.

6. 3. Elevated HcG Levels For various reasons, doctors may monitor HcG (human chorionic gonadotropin) levels. HcG is a hormone detectable in pregnant women's blood or urine about 10 days post- conception; it increases at a rapid rate, peaking about 10 weeks into the pregnancy. Twins may produce an elevated level of HcG. However, the standard HcG level for twins also falls within the normal range for singletons.

7. 4. Abnormal AFP Test Results AFP (Alphafetoprotein) screening is a blood test performed on pregnant mothers during the second trimester. Also known as maternal serum screening or triple marker screen, it is used to identify increased risks of certain birth defects. A twin pregnancy can produce an usually high -- or "positive -- result.

8. 5. Measuring Large for Gestational Age Throughout the pregnancy, the doctor may measure the height of the uterine fundus (from the top of the pubic bone to the top of the uterus) as a way of indicating gestational age. A twin or multiple pregnancy may cause the patient’s uterus to expand beyond the range of a single pregnancy. However, other factors may also increase the measurements.

9. 6. Weight Gain Just as a multiple pregnancy may cause a mother to measure large, it may also result in an increased weight gain. How much weight a woman gains can vary depending on her height, body type and how much she weighed pre-pregnancy. Increased or rapid weight gain more than likely reflects eating choices rather than twins; generally, mothers of twins only gain about 10 lbs. more than singleton mothers

10. 7. Excessive Morning Sickness About 50% of pregnant women experience some amount of vomiting or nausea associated with their pregnancy. Moms of multiples certainly aren't exempt, but neither are they doomed to a double dose. Only about 15% of mothers reported enhanced morning sickness symptoms as an indicator of their multiple pregnancies. Experiences vary widely -- some do, some don't.

11. 8. Early/Frequent Fetal Movement Feeling a baby -- or babies -- move inside the womb is one of the most thrilling aspects of pregnancy. Although many moms of multiples do experience more frequent or earlier fetal movement, there is considerable disagreement among medical professionals on the subject. For some women, recognizable feelings of movement occur earlier in subsequent pregnancies, whether there is one baby or more.

12. 9. Extreme Fatigue This is the most commonly reported complaint during pregnancy with multiples. Sleepiness, lethargy and exhaustion during the first trimester can be enhanced because the body is working overtime to nurture more than one baby. In some cases, the fatigue can be attributed to other factors (work, stress, poor nutrition, having other children), but it can also be an indication of multiples.

13. 10. History/Hunches While the other items in this list refer to some kind of visible evidence -- exaggerated symptoms, abnormal test results, etc. – don’t totally disregard the power of a mother's intuition. A family history of multiples or a powerful hunch can be convincing indicators.

14. Outline: Part I

16.  Twins are two offspring resulting from the same pregnancy, usually born in close succession. They can be the same or different sex. Twins can either be monozygotic (identical) or dizygotic (fraternal).offspring resulting from the same pregnancy, usually born in close succession. They can be the same or different sex. Twins can either be monozygotic (identical) or dizygotic (fraternal).  The general term for more than one offspring in the same pregnancy (multiple birth) is multiples; a fetus which develops alone in the womb is called a singleton.multiple birth) is multiples; a fetus which develops alone in the womb is called a singleton.  Due to the limited size of the mother's womb, multiple pregnancies are much less likely to carry to full term than singleton births, with twin pregnancies lasting only 37 weeks (3 weeks less than full term) on average. Since premature births can have health consequences for the babies, twin births are often handled with special precautions.premature births can have health consequences for the babies, twin births are often handled with special precautions.

17.  There are five common variations of twinning. The three most common variations are all dizygotic:  male-female twins are the most common result, at about 40 percent of all twins born  female DZ twins (sometimes called sororal twins)  male DZ twins.

18.  The other two variations are monozygotic twins:  female MZ twins  male MZ twins (least common).

19.  Dizygotic twins (commonly known as fraternal twins, but also referred to as non-identical twins or biovular twins) usually occur when two fertilized eggs are implanted in the uterine wall at the same time. When two eggs are independently fertilized by two different sperm cells, DZ twins result. The two eggs, or ova, form two zygotes, hence the terms dizygotic and biovular.fertilized eggs are implanted in the uterine wall at the same time. When two eggs are independently fertilized by two different sperm cells, DZ twins result. The two eggs, or ova, form two zygotes, hence the terms dizygotic and biovular.  Dizygotic twins, like any other siblings, have an extremely small chance of having the exact same chromosome profile. Like any other siblings, DZ twins may look similar, particularly given that they are the same age. However, DZ twins may also look very different from each other. They may be of different sexes or the same sex. The same holds true for brothers and sisters from the same parents, meaning that DZ twins are simply brothers and/or sisters who happen to have the same age.siblings, DZ twins may look similar, particularly given that they are the same age. However, DZ twins may also look very different from each other. They may be of different sexes or the same sex. The same holds true for brothers and sisters from the same parents, meaning that DZ twins are simply brothers and/or sisters who happen to have the same age.

20.  Monozygotic twins, frequently referred to as identical twins, occur when a single egg is fertilized to form one zygote (monozygotic) which then divides into two separate embryos. They are the same sex and their traits and physical appearances are very similar but not exactly the same; although they have nearly identical DNA. The two embryos develop into fetuses sharing the same womb. When one egg is fertilized by one sperm cell, and then divides and separates, two identical cells will result. If the zygote splits very early (in the first two days after fertilization), each cell may develop separately its own placenta (chorion) and its own sac (amnion). These are called dichorionic diamniotic (di/di) twins, which occurs 18–36% of the time. Most of the time in MZ twins the zygote will split after two days, resulting in a shared placenta, but two separate sacs. These are called monochorionic diamniotic (mono/di) twins, occurring 60– 70% of the time.egg is fertilized to form one zygote (monozygotic) which then divides into two separate embryos. They are the same sex and their traits and physical appearances are very similar but not exactly the same; although they have nearly identical DNA. The two embryos develop into fetuses sharing the same womb. When one egg is fertilized by one sperm cell, and then divides and separates, two identical cells will result. If the zygote splits very early (in the first two days after fertilization), each cell may develop separately its own placenta (chorion) and its own sac (amnion). These are called dichorionic diamniotic (di/di) twins, which occurs 18–36% of the time. Most of the time in MZ twins the zygote will split after two days, resulting in a shared placenta, but two separate sacs. These are called monochorionic diamniotic (mono/di) twins, occurring 60– 70% of the time.

21.  In about 1–2% of MZ twinning the splitting occurs late enough to result in both a shared placenta and a shared sac called monochorionic monoamniotic (mono/mono) twins. Finally, the zygote may split extremely late, resulting in conjoined twins. Mortality is highest for conjoined twins due to the many complications resulting from shared organs. Mono/mono twins have an overall in-utero mortality of about 50 percent, principally due to cord entanglement prior to 32 weeks gestation. If expecting parents choose hospitalization, mortality can decrease through consistent monitoring of the babies. Hospitalization can occur beginning at 24 weeks, but doctors prefer a later date to prevent any complications due to premature births. The choice is up to the parents when to start hospitalization. Many times, monoamniotic twins are delivered at 32 weeks electively for the safety of the babies. In higher order multiples, there can sometimes be a combination of DZ and MZ twins.conjoined twins. Mortality is highest for conjoined twins due to the many complications resulting from shared organs. Mono/mono twins have an overall in-utero mortality of about 50 percent, principally due to cord entanglement prior to 32 weeks gestation. If expecting parents choose hospitalization, mortality can decrease through consistent monitoring of the babies. Hospitalization can occur beginning at 24 weeks, but doctors prefer a later date to prevent any complications due to premature births. The choice is up to the parents when to start hospitalization. Many times, monoamniotic twins are delivered at 32 weeks electively for the safety of the babies. In higher order multiples, there can sometimes be a combination of DZ and MZ twins.  Mono/di twins have about a 25 percent mortality due to twin-to-twin transfusion syndrome. Di/di twins have the lowest mortality risk at about 9 percent, although that is still significantly higher than that of singletons.twin-to-twin transfusion syndrome. Di/di twins have the lowest mortality risk at about 9 percent, although that is still significantly higher than that of singletons.  Monozygotic twins are genetically identical (unless there has been a mutation in development) and they are always the same sex.

22. Zygosity, chorionicity and amniocity  The two types of twins, monozygotic and dizygotic, are generally referred to as zygocity. Zygocity reflects the genetic type of twins. Two others terms define twin types: chorionity and amniocity. Chorionity refers to the number of chorionic sacs, while amniocity refers to the number of amniotic sacs. The number of chorionic and amnionic sacs can sometimes reveal the zygocity. Monoamniotic twins indicate monozygotic twins. However, two placentas does not provide information about zygocity since monozygotic twins can have two placentas. Chorionicity and amniocity are a result of the division time. Dichorionic twins divide within the first 4 days. Monoamnionic twins divide after the first week.

23. Complications Vanishing twins  Researchers suspect that as many as 1 in 8 pregnancies start out as multiples, but only a single fetus is brought to full term, because the other has died very early in the pregnancy and has not been detected or recorded. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes. This is known as vanishing twin syndrome. obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes. This is known as vanishing twin syndrome.

24. Conjoined twins  Conjoined twins (or the term "Siamese twins") are monozygotic twins whose bodies are joined together during pregnancy. This occurs where the single zygote of MZ twins fails to separate completely, and the zygote starts to split after day 13 following fertilization. This condition occurs in about 1 in 50,000 human pregnancies. Most conjoined twins are now evaluated for surgery to attempt to separate them into separate functional bodies. The degree of difficulty rises if a vital organ or structure is shared between twins, such as the brain, heart or liver.brain, heart or liver.

25. Partial molar twins  A very rare type of parasitic twinning is one where a single viable twin is endangered when the other zygote becomes cancerous, or molar. This means that the molar zygote's cellular division continues unchecked, resulting in a cancerous growth that overtakes the viable fetus. Typically, this results when one twin has triploidy, resulting in little or no fetus and a cancerous, overgrown placenta, resembling a bunch of grapes.triploidy, resulting in little or no fetus and a cancerous, overgrown placenta, resembling a bunch of grapes.

26. Miscarried twin  Occasionally, a woman will suffer a miscarriage early in pregnancy, yet the pregnancy will continue; one twin was miscarried but the other was able to be carried to term. This occurrence is similar to the vanishing twin syndrome, but typically occurs later than the vanishing twin syndrome. miscarriage early in pregnancy, yet the pregnancy will continue; one twin was miscarried but the other was able to be carried to term. This occurrence is similar to the vanishing twin syndrome, but typically occurs later than the vanishing twin syndrome.

27. Low birth weight  Twins typically suffer from the lower birth weights and greater likelihood of prematurity that is more commonly associated with the higher multiple pregnancies. Throughout their lives twins tend to be smaller than singletons on average.birth weights and greater likelihood of prematurity that is more commonly associated with the higher multiple pregnancies. Throughout their lives twins tend to be smaller than singletons on average.

28. Twin-to-twin transfusion syndrome  Monozygotic twins who share a placenta can develop twin-to-twin transfusion syndrome. This condition means that blood from one twin is being diverted into the other twin. One twin, the 'donor' twin, is small and anemic, the other, the 'recipient' twin, is large and polycythemic. The lives of both twins are endangered by this condition. anemic, the other, the 'recipient' twin, is large and polycythemic. The lives of both twins are endangered by this condition.

29. The Heart of the matter: Part II

30. Zygosity  Multiple gestations can occur several ways, and the term Zygosity refers to the number of zygotes involved.  Multiple fetuses from one zygote are called monozygotic; Dizygotic means two zygotes originated.

31. Monozygotic Twins

32. Dizygotic Twins

33. Monozygotic Twinning  Arising from a single fertilized ovum, monozygotic twins are considered TRUE or IDENTICAL twins. A single ovum is fertilized by a single sperm, and the twins are always of the same gender.  This type of twinning occurs about 2-4 times per 1,000 pregnancies. It is associated with increased complications.

34.  A variety of placental and membrane combinations can occur in monozygotic twinning. The specific configuration is determined by when the division occurs, and results in a varied number of placentas, chorionic membranes, and amniotic membranes.  It is imperative to establish sonographically if there are separate amniotic cavities.

35. Sonographic considerations  Careful evaluation of placental number and presence and appearance of membranes is essential.  First trimester Sonography is more accurate for determining chorionicity and amnioicity

36. Monozygotic twins: One turns into two Dizygotic twins: Mom has two kids: but at the same time.

37. Twinning Chart

38. Dizygotic Twinning  Dizygotic twins arise from separate ova fertilized by separate sperm cells, and produce “fraternal” twins. The  Twins may be the same or different genders. This type of twinning occurs about 1 in 83 conceptions.  Two zygotes will always have two amnions, two chorions and two separate placentas (that may  Appear fused). As the sacs grow in size, the chorion levae and decidua capsularis thin, and likewise the  Intertwine membrane.

39. Some factors associated with Dizygotic twinning include:  Recent cessation of long term oral contraceptives  Maternal family history of multiple gestations  Maternal age 35-40 years old

40. Sonographic findings of Dizygotic twins  Can identify dichorionic features most easily in early pregnancy  Presence of a “thick” membrane  Possible identification of two separate placental sites

41. Dizygotic Twinning Chart

42. Clinical findings in twin Pregnancy  Typical signs of pregnancy  Increased maternal serum AFP  Earlier and more severe pressure problems in the pelvis such as hemorrhoids, constipation  Backaches, difficulty breathing  Increased fetal activity  Increased uterine size  Shortness of breath

43. Dichorionic, Diamniotic, Double Placenta  May be fused…Sonographically identical to Dizygotic results when division occurs before the morula.  Staged (day 5) after conception.

44. Dichorionic-Diamniotic Twins

45. Monchorionic, Diamniotic, Single Placenta  MOST COMMON: Results when division occurs after differentiation of the chorion but before differentiation of the amnion (5-10 days after conception).

46. Monchorionic, Diamniotic, Single Placenta

47.  Monochorionic, Monoamniotic, Single placenta  LEAST COMMON: Results when division occurs after differentiation of the chorion and amnion  days 10-13 post conception.

48. Monochorionic, Monoamniotic, Single placenta

49.  IF THE DIVISION OF THE CONCEPTUS OCCURS AFTER THE SECOND WEEK, THEN CONJOINED TWINS RESULTS.

50.  CLINICAL COMPLICAITONS ASSOCIATED WITH TWIN PREGNANCY  The stress of multiple pregnancy can affect the maternal respiratory, gastrointestinal, Renal and musculoskeletal systems.

51. Maternal complications.  Women with multiple gestations are at risk for a number of complications, including:  Anemia  Urinary tract infection  Preeclampsia/eclampsia  Prepartum hemorrhage

52. Fetal complications  Fetuses are closely monitored throughout the pregnancy. Complications that may occur include:  Premature delivery  Difficulty delivery due to abnormal presentation  Prolapsed, entanglement or compression of an umbilical cord  Hypoxia of one second twin due to premature separation of the placenta  Growth restriction due to placental insufficiency.

53. COMPLICATIONS OF TWIN GESTATIONS  Vanishing twin:  The resorption of a nonviable fetus in a twin gestation that was previously demonstrated  Sonographically. The Vanishing twin sac may mimic an implantation bleed in the endometrial Cavity, or a submembranous bleed.

54. Vanishing Twin Cont.  Sonographic findings  Failure to demonstrate multiple sacs on subsequent sonograms  Failure of sac growth in a twin  Irregular marginated sac

55. Vanishing Twin

56. Twin-Twin Transfusion Syndrome TTTS  This serious condition occurs in monozygotic twins with a shared, Monochorionic placenta  And is referred to as Cross-transfusion or third circulation.  It results from an anomalous development of the vascular supply of each twin to the shared placenta (with artery-to-vein anastomosis). In its most serious form, significant artery to vein  Anastomosis shunt blood away from the donor twin to the recipient twin.

57. TTTS Sonographic findings DONOR TWIN  Small for dates  Oligohydramnios  STUCK twin with empty bladder and restricted movement

58. TTTS RECIPIENT TWIN  Hydropic  Ascites  Enlarged liver, heart and kidneys  Polyhydramnios

59. Twin-Twin Transfusion Syndrome

61. TWIN EMBOLIZATION SYNDROME  The passage of thromboplastic material or blood clots from a dead Monchorionic twin to the remaining live twin through shared intraplacental vasculature can result in neurological, Gastrointestinal or genitourinary defects.  Sonographic findings  Intrauterine death of co-twin  Hydrops  Polyhydramnios  Intraparenchymal hemorrhage  Ventriculomegaly, microcephaly  Enlarged, echogenic kidneys

62. Conjoined Twins  The incomplete division of a fertilized ovum after 13 days post-conception results in conjoined  Twins.  They are describe by the site of union

63.  THORACOPAGUS (chest) most common  PYGOPAGUS (sacrum)  CRANIOPAGUS (head)  OMPHALOPAGUS (abdominal wall)  ISCHIOPAGUS (Pelvis)

64. Conjoined Twins-THORACOPAGUS (chest)

66. PYGOPAGUS (sacrum)

68. CRANIOPAGUS (head)

70. OMPHALOPAGUS (abdominal wall)

72. ISCHIOPAGUS (Pelvis)

73. Conjoined Twins cont.  Sonographic findings  Single thorax (Thoracopagus)  Grossly abnormal fused abdomen (Omphalopagus)  Fused head (Craniopagus)

74. Acardiac Twin (Parabiotic Twin)  A bizarre form of monozygotic twinning in which a severely malformed Acardiac (and often anencephalic) twin is perfused by the normal twin. Perfusion is accomplished through two anastomosis, one vein to vein and one artery to artery. The non-viable, anomalous twin usually does not have a heart (Acardiac). Due to the increased cardiac burden on the PUMP twin, it is at risk for high-output congestive heart failure and Hydrops.

75. Acardiac Twin (Parabiotic Twin) cont.  Pathologically, the following characteristics are seen:  Extremely limited upper body development  Absence of head or, it present may be small and Holoprosencephaly  Absent or hypoplastic thorax, cervical spine and arms  Absent heart, lungs and abdominal viscera  Dorsal, multi-loculated cystic hygroma

76. Acardiac Twin (Parabiotic Twin) cont.  Sonographic findings:  Polyhydramnios  Monozygotic or Monchorionic/Monoamniotic

77. Acardiac Twin

78. Homework  Submit images depicting the following:  Monozygotic twins  Dichorionic Diamniotic twins  Hydropic twin  Discordant dichorionic-diamniotic sacs  Dichorionic Diamniotic twins  Monochorionic Diamniotic twins  Monochorionic, Monoamniotic twins  Stuck twins in TTTS  Omphalopagus  Acardiac Parabiotic twin

79. Callen Homework  Chorionicity equals the number of gestational sacs. Explain.  Amnionicity equals the number of yolk sacs. Explain.  When and why is the thickness of the intertwine membrane important?  What is a “vanishing” twin?  How does a conjoined twin come into being? What types of conjoined twins are there?

80. Part III - recap

82. Monozygotic twins  Arise from a single ovum and produce "true" or identical twins. When a single  ovum is fertilized by a single sperm.  Twins are always of the same gender.  Occurs about 2 - 4 times per 1,000 pregnancies.  Associated with increased complications

83. Monozygotic twins PLACENTAL VARIATIONS A variety of placental and membrane combinations can occur in monozygotic twinning. The specific configuration is determined by the timing of the division of the embryonic disk and results in a varied number of placentas, chorionic membranes and amniotic membranes.

84. Monozygotic twins  Dichorionic, diamniotic, double placenta may be fused  IDENTICAL TO DIZYGOTIC  results when division occurs before the morula stage (Day 5) and implantation

85.  Monochorionic, diamniotic, single placenta: MOST COMMON  Results when division occurs after differentiation of the amnion  (5 - 10 days after conception)  Monochorionic, monoamniotic, single placenta: LEAST COMMON  Results when division occurs after differentiation of the trophoblast  (days 10 - 14)  IF DIVISION OF THE CONCEPTUS OCCURS AFTER THE SECOND WEEK, CONJOINED TWINS RESULT

86. Dizygotic twins  Always have two amnions, two chorions and two separate placentas. The placentas may be fused. As the sacs grow in size, the chorion levae and decidua capsularis become thin and the space between the sacs disappears.

87.  Dizygotic twins arise from separate ova fertilized by separate sperm cells and produce "false" or fraternal twins.  May be the same or different gender.  Occurs about 1 in 83 conceptions.  Some factors associated with dizygotic twinning include:  Recent cessation of long term oral contraceptives  Maternal family history of twinning  Maternal age 35 - 40 year old

88. SONOGRAPHIC FINDINGS:  Can differentiate monozygotic from dizygotic in early pregnancy  Presence of a "thick" membrane  Identification of two separate placental sites

89. CLINICAL SIGNS  Typical signs of pregnancy  Earlier and more severe pressure problems in the pelvis such as hemorrhoids, constipation, backaches, difficulty breathing  increased fetal activity  Increased uterine size  Shortness of breath

92. CLINICAL COMPLICATIONS ASSOCIATED WITH TWIN PREGNANCY: The stress of multiple pregnancy can affect the maternal respiratory, gastrointestinal, renal and musculoskeletal systems.  Maternal complications include:  Anemia  Urinary tract infection  Preeclampsia/eclampsia  Prepartum hemorrhage

93. Fetal complications may include:  Premature delivery  Difficult delivery due to abnormal position  Prolapse, entanglement or compression of an umbilical cord  Hypoxia of the second twin due to premature separation of the placenta  Growth retardation due to placental insufficiency

94. Vanishing twin  The resorption of a nonviable gestation that was previously demonstrated sonographically. May represent resorption of blood in the endometrial cavity  related to implantation bleeding.  SONOGRAPHIC FINDINGS:  Failure to demonstrate multiple gestations on subsequent sonograms  Failure of sac growth in a twin  Irregularly marginated sac

95. Vanishing Twin

96. Twin-twin transfusion syndrome  This serious condition occurs in monozygotic twins with a fused placenta and is also referred to as "cross-transfusion" or "third circulation".  It results from an anomalous development of the vascular supply to each twin (artery to vein anastomosis).  In its most serious form, significant artery to vein anastomoses shunt blood away from the donor twin to the recipient twin

97. Twin-twin transfusion syndrome SONOGRAPHIC FINDINGS:  Donor twin  Small for dates  Oligohydramnios  “Stuck twin” with empty bladder and restricted movement

98. TTTS (stuck Twin)

99. Recipient Twin

100. Recipient twin  Hydropic  Ascites  Enlarged liver, heart and kidneys  Polyhydramnios

101. Twin embolization syndrome  The passage of thromboplastic material or blood clots from a dead monochorionic twin to the remaining live twin through shared intraplacental vasculature.  Neurological, gastrointestinal or genitourinary deficits may result from infarction.

102.  SONOGRAPHIC FINDINGS:  Intrauterine death of co-twin  Hydrops  Polyhydramnios  Ventriculomegaly, porencephaly, microcephaly  Enlarged, echogenic kidneys

104. Stuck twin (fetus papyraceous)  The presence of a small, growth retarded twin an oligohydramniotic sac. May be the result of twin to twin transfusion syndrome. The restricted fetus has limited motion of the extremities.  SONOGRAPHIC FINDINGS:  Twin pregnancy  One twin in sac with normal fluid  One twin in sac with oligohydramnios  Restricted movement of "stuck" twin

105. Conjoined twins (Siamese)  The incomplete division of a fertilized ovum between the 8th and 14th day results in conjoined twins. They are described by the site of union:  Thoracopagus (chest) MOST COMMON  Pygopagus (sacrum)  Craniopagus (head)  Omphalopagus (abdominal wall)  Ischiopagus (pelvis)

108. SONOGRAPHIC FINDINGS:  Movement in unison, no independent major movements  Single thorax (thoracopagus)  Grossly abnormal  Fused abdomen (omphalopagus)  Fused head (craniopagus)

109. Acardiac twin (parabiotic twins)  A bizarre malformation of monozygotic twinning in which a severely malformed  twin is maintained by the normal twin. Perfusion is accomplished through two  anastomoses, one vein to vein and one artery to artery. The non- viable usually  does not have a heart (acardiacus) and would have been a simple first trimester  twin death. Due to the increased cardiac burden on the pump twin, it is at risk for  high-output congestive heart failure.  PATHOLOGY:  Extremely limited upper body development  Absence of head or, if present, small with holoprosencephaly  Absent or hypoplastic thorax, cervical spine and arms  Absent heart, lungs and abdominal viscera  Dorsal, multiloculated cystic hygroma

110.  To Summarize…

111. What is monozygotic twinning?  Monozygotic twinning arises from a single fertilized ovum that divides into two separate but identical embryos.

112. What are the possibilities placental/membrane configurations for monozygotic twins?  Monozygotic twins, depending on when the separation takes place after fertilization, can result in:  two placentas, two chorions, and two amnions  a single placenta, one chorion, and two amnions  a single placenta, one chorion, and one amnion

113. What is dizygotic twinning?  Dizygotic twinning occurs when two separate ovum are fertilized, and two embryos with separate blastocysts result.

114. What are the possible placental/membrane configurations for dizygotic twins?  Dizygotic twins, then can only have the following placental and membrane configuration:  Two placentas, two chorions, and two amnions.

115. Twin-twin transfusion syndrome (TTTS) is a serious complication of monozygotic twinning. What is the etiology of this complication?  Twin-twin transfusion syndrome occurs when there is a vascular anastomosis in the shared placenta between the two fetuses. Blood in shunted away from one twin, increasing perfusion to the other twin.

116. What are the sonographic findings for the donor twin in TTTS?  The donor twin ( from whom blood is shunted) sonographically is  small for dates  has Oligohydramnios  has an empty bladder and appears STUCK with restricted movement

117. What are the sonographic findings for the recipient twin in TTTS?  The recipient twin sonographically is  Hydropic with ascites  has organ-megaly (enlarged liver, heart and kidneys)  has Polyhydramnios

118. Twin embolization syndrome occurs when one of the twin’s demises in utero and thromboplastic material passes to the remaining twin via shared intraplacental vasculature. What are the complications for the surviving twin?  The surviving win in twin embolization syndrome is at risk for  hydrops  Polyhydramnios  Intraparenchymal hemorrhage  ventriculomegaly, porencephaly, microcephaly  Enlarged echogenic kidneys

119. Define Thoracopagus  Thoracopagus is twins who are conjoined at the thorax (chest)

120. Define Omphalopagus  Omphalopagus is twins who are conjoined at the abdominal wall

121. Define Craniopagus  Craniopagus is twins who are conjoined at the cranium (head)

122. How do the conjoined anomalies occur?  Conjoined twins occur when the fertilized ovum fails to completely separate, after day 13 post conception.

123. The end. Oh wait…your 4 o’clock patient just showed up.