Multiple Births

Multiple gestation occurs frequently in pregnancy. The most common is twinning, which occurs in about one in every 80 pregnancies. There are two types of twins: monozygous or "identical" and dizygous or "fraternal." The monozygous twin rate is 1 in every 200 pregnancies. It results from a single ovulation with subsequent splitting of the developing egg within the first 14 days. There is no familial tendency. Dizygous twinning results from double ovulation and fertilization and is probably determined by higher gonadotropin secretion rates. The rate of dizygous twinning is variable and is influenced by heredity (transmitted autoso-mally but expressed only in the mother), race (as high as 1 in 23 births in some West African races; as low as 1 in 300 births in Mongolian races), maternal age (increased frequency with increasing age), and drugs (incidence of twinning is 6.6% with the use of Clomid®). Examination of the placenta of multiple births is important because of the two- to three-fold higher incidence of structural defects in monozygous twins and increased potential for successful future transplant between monozygous twins. Monochorionic placentas are invariably fused and about 75% of the infants are identical twins. Dichorionic placentas may be fused or separate. Infants with a dichorionic fused placenta may be identical (monozygous) or fraternal (dizygous). The membrane which separates the two fetal cavities is the key to the evaluation of twin placenta. Typically, this runs across the middle of the fused placenta. In monochorionic twins, with one chorion covering two amnia, the dividing membrane consists of two translucent amnionic layers which can be pulled with ease from the placental surface. In 1% of monozygotic twinning, the placenta will be monochorionic-monoamnionic. In conjoined twinning, the placenta is also monochorionic-monoamnionic. In dichorionic twins, with two amnia, the dividing membrane consists of four layers, two chorionic and two amnionic; it is opaque, thicker, and does not separate from the placental surface without tearing.

Monochorionic
Figure 2.1. These infants are normal, identical triplets born at 32 weeks gestation. They initially had mild respiratory distress, but improved rapidly. (Cabera-Meza, G.)
Types Twin Placentas
Male Identical Triplets
Figure 2.3. A triplet placenta showing a vela-mentous insertion of the cord in one of the triplets. Note that the placentas are fused and thus the pregnancy could be monozygotic.

Figure 2.4. The fetal surfaces of two completely separated twin placentas. These are always dizygotic.

Figure 2.5. This low-power histologic section demonstrates that an amnion can be identified on each side of two choria. Thus, this is an example of a dichorionic-diamnionic placenta. This type of dividing membranes is typically seen in all dizygotic twinning and in about 20 to 25% of monozy-gotic twinning.

Figure 2.5. This low-power histologic section demonstrates that an amnion can be identified on each side of two choria. Thus, this is an example of a dichorionic-diamnionic placenta. This type of dividing membranes is typically seen in all dizygotic twinning and in about 20 to 25% of monozy-gotic twinning.

Monozygotic Membrane

Figure 2.6. The fetal surface of this fused, twin placenta shows the dividing membranes. In this placenta, histologic examination showed that there were two amnia and a single chorion (diamnionic-monochorion-ic). These twins would thus be monozygotic.

Figure 2.6. The fetal surface of this fused, twin placenta shows the dividing membranes. In this placenta, histologic examination showed that there were two amnia and a single chorion (diamnionic-monochorion-ic). These twins would thus be monozygotic.

Twin Placenta Histology Compared
Twin Placenta Histology ComparedPlacenta Chorion Amnion Image Histology
Figure 2.7. Histology of the membranes of the same placenta shows the double amnion on the outer surfaces with a single chorion (diamnionic-monochorionic ).
Fused Placenta
Figure 2.8. On the fetal surface of this fused, twin placenta, the dividing membrane is very thin and clear, suggesting that this is a monozygotic pregnancy. This was confirmed by histologic examination showing a single chorion. (Finegold, M.)
Twin Placenta Histology Compared
Figure 2.9. The histologic appearance of the dividing membranes in twin placentas are compared in diis figure. On the left, note die diamiiioiiic-monochori-onic twin placenta, and on the right, note the diamnionic-dichorionic twin placenta.

Figure 2.10. Note the two umbilical cords inserting into the fetal surface of the placenta without the presence of dividing membranes. This is typical of a monoamnionic-monochorionic twin placenta, which occurs in 1% of twin pregnancies.

Figure 2.11. The fetal surface of a monoamnionic-monochorionic twin placenta, showing the insertion of two separate umbilical cords. (Sotelo-

Figure 2.12. Close-up of the above placenta shows anastomosis of the vessels between the two umbilical cords. This results in a twin (feto-fetal) transfusion syndrome. (Sotelo-Avila, C.)

Figure 2.10. Note the two umbilical cords inserting into the fetal surface of the placenta without the presence of dividing membranes. This is typical of a monoamnionic-monochorionic twin placenta, which occurs in 1% of twin pregnancies.

Feto Fetel Transfusion Syndrome

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Twin Placenta Dividing Membranes

Figure 2.13. The fetal surface of a monoamnionic-monochorionic twin placenta showing the entanglement of the two umbilical cords resulting in fetal anoxia and fetal distress with meconium passage. Note the meconium-stained appearance of the fetal surface of the placenta. Entanglement of the cords is a complication which may occur because of a lack of a dividing membrane in monoamnionic-mono-chorionic twins. (Karishan, B.)

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Foetus Papyraceus

Figure 2.15. The fetal surface of this monoamnionic-monochorion-ic placenta in conjoined twins shows the insertion of the two umbilical cords, but note that these fuse and present as a single fused cord in thoracopagus twins. (Sotelo-Avila, C.)

Figure 2.14. Another example of entangled cords in a monoamnionic-monochorion-ic twin placenta.

Figure 2.15. The fetal surface of this monoamnionic-monochorion-ic placenta in conjoined twins shows the insertion of the two umbilical cords, but note that these fuse and present as a single fused cord in thoracopagus twins. (Sotelo-Avila, C.)

Figure 2.16. The appearance of the umbilical cords in a twin pregnancy. Note die small size of the umbilical cord in the infant who was growth-retarded as compared to the normal size of the umbilical cord in the normal twin.

Figure 2.16. The appearance of the umbilical cords in a twin pregnancy. Note die small size of the umbilical cord in the infant who was growth-retarded as compared to the normal size of the umbilical cord in the normal twin.

Mono Mono Twins Umbilical Cord

Figure 2.17. These infants born as stillbirths at 30 weeks gestation are an example of twin (feto-fetal) transfusion syndrome. In this syndrome, vascular anastomoses permit the transfer of arterial blood under high pressure from the twin on the right (donor) to the low pressure venous system of the other twin (recipient). The donor twin is thus kept hypovolemic, dehydrated, malnourished, or even in shock. His organs are small and his amniotic fluid is decreased. The recipient twin becomes hypervolemic, edematous, and plethoric (polycythemic). His organs are large, he may have congestive failure and his amniotic fluid is increased.

Figure 2.17. These infants born as stillbirths at 30 weeks gestation are an example of twin (feto-fetal) transfusion syndrome. In this syndrome, vascular anastomoses permit the transfer of arterial blood under high pressure from the twin on the right (donor) to the low pressure venous system of the other twin (recipient). The donor twin is thus kept hypovolemic, dehydrated, malnourished, or even in shock. His organs are small and his amniotic fluid is decreased. The recipient twin becomes hypervolemic, edematous, and plethoric (polycythemic). His organs are large, he may have congestive failure and his amniotic fluid is increased.

Plethoric Appearance

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Figure 2.18. These monozygotic twins at birth represent another example of twin transfusion syndrome. The birth weight of the twin on the left was 3000 g widi a central hematocrit of 86%. The birdi weight of the twin on the right was 2230 g with a central hematocrit of 27%. Twin transfusion syndrome occurs only in moiiochorionic twins. It occurs in 15 to 30% of moiiochorionic pregnancies and is defined in terms of a difference of greater dian 250 g birth weight and/or 20% difference in the central hematocrit between the twins. Twins in this syndrome usually do not look identical at birth although in fact they are monozygotic.

Identical Triplets

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Newborn Hematocrit
Figure 2.19. In these infants with twin transfusion syndrome, the difference in birth weight was only 180 g and the difference in central hematocrit was 32%. Thus, these infants represent a mild example of twin transfusion syndrome.

Figure 2.20. The maternal surface of a monozygotic twin placenta in infants who had the twin transfusion syndrome. Note on die left the congested appearance of the portion of the placenta supplying the recipient twin who had a central hematocrit of 69%, and note on the right die much paler appearance of the placenta supplying the donor twin who had a central hematocrit of 45%. (Singer, D.)

Figure 2.21. The fetal surface of the same placenta as in Figure. 2.20 showing the congested appearance on the left of the recipient portion of the twin placenta and the pallor on the right of the donor portion of the twin placenta. These vascular connections may be artery-to-artery, vein-to-vein, or artery-to-vein. Any form may significantly affect the fetuses physiologically and clinically.

Figure 2.22. The fetal surface of placentas in twin transfusion syndrome showing the anastomoses between the two fetal circulations following the injection of infant formula, which is used as a contrast medium. Note that on the fetal surface of the placenta arteries always cross over veins. The anastomosis between an artery on the left and a vein on the right is shown at the junction of the left third and the right two-thirds of the figure.

Figure 2.22. The fetal surface of placentas in twin transfusion syndrome showing the anastomoses between the two fetal circulations following the injection of infant formula, which is used as a contrast medium. Note that on the fetal surface of the placenta arteries always cross over veins. The anastomosis between an artery on the left and a vein on the right is shown at the junction of the left third and the right two-thirds of the figure.

Lymph Vein Anastomosis

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Figure 2.23. This close-up view clearly shows the artery-to-vein anastomosis.

Figure 2.24. Another example of an injection of infant formula filling the arteries which cross over the veins in this vessel anas-

tomosis.

Figure 2.24. Another example of an injection of infant formula filling the arteries which cross over the veins in this vessel anas-

Vanishing Twin Syndrome Fetus Papyraceus

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Lithopedion Fetus Photos
Figure 2.25. In extreme cases the transfusion syndrome may cause the death of one twin resulting in a fetus papyraceus. In this figure, there is an extrachorial placenta with a fetus papyraceus attached.
Lithopedion Fetus Photos

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Fetus Papyraceus
Figure 2.27. Another example of the twin transfusion syndrome. Note the maternal surface of the placenta showing the congested recipient placenta on the left and the pale donor placenta on the right with an attached fetus papyraceus.

Figure 2.28. The fetus papyraceus may calcify and result in a lithopedion ("stone child") as shown in this figure.

Fetus Papyraceus

Figure 2.29. A stillborn male infant with a birthweight of 1170 g and length of 34 cm is an example of acardius acephalus. This is one of the acardiac anomalies which occurs as a consequence of abnormal umbilical artery-to-artery anastomoses between two fetuses in the presence of a fused placenta. It is sometimes referred to as the TRAP (twin-reversed-arterial-perfusion) sequence. (Klima, T.)

Figure 2.29. A stillborn male infant with a birthweight of 1170 g and length of 34 cm is an example of acardius acephalus. This is one of the acardiac anomalies which occurs as a consequence of abnormal umbilical artery-to-artery anastomoses between two fetuses in the presence of a fused placenta. It is sometimes referred to as the TRAP (twin-reversed-arterial-perfusion) sequence. (Klima, T.)

Twin Reversed Arterial Perfusion

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Figure 2.30. A close-up of the abdomen of the same infant shows an omphalocele; there was also hydrops, pulmonary agenesis, and polyhydramnios. Acardiac anomalies include three groups: acephalus in 60 to 75% of cases, amorphus in 20% of cases, and a well-formed head and body in 10% of cases. (Klima, T.)

Acardiac Acephalus Twins

Figure 2.31. The fused placenta of the same infant with acardius acephalus shown in Figure 2.29 and 2.30. Note the large cord of the "normal" infant which had three vessels and the small cord of the infant with acardius acephalus which had two vessels. There were no separating membranes between the two cords. Note the large anastomoses between the placentas. (Klima, T.)

Figure 2.31. The fused placenta of the same infant with acardius acephalus shown in Figure 2.29 and 2.30. Note the large cord of the "normal" infant which had three vessels and the small cord of the infant with acardius acephalus which had two vessels. There were no separating membranes between the two cords. Note the large anastomoses between the placentas. (Klima, T.)

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Acardius Anceps
Figure 2.32. An acardius acephalus infant delivered at 30 weeks gestation. The upper body and shoulders form a fleshy mass capped by a tuft of short hairs. The lower body has two well-formed legs but has clubbed, bifid feet with two toes. (Klima, T.)

Figure 2.33. Radiograph of the infant with acardius acephalus. Note the lack of cranial development. Two clavicles and scapulae are present. The vertebral column is normal. The chest is narrow due to lack of the heart and hypoplastic lungs. The pelvis and lower extremities are well mineralized and relatively normal except for lack of some metatarsal bones.

Figure 2.34. The twin with the dominant heart of the same pregnancy often shows additional anomalies such as limb reduction defects. These have been attributed to em-bolic disease consequent upon stasis in the acardiac fetus. This twin had some limb anomalies which included fusion of digits of the left hand as seen in this figure.

Figure 2.35. This is the same infant showing anomalies of both feet.

Figure 2.36. The placenta of the infants described above showing two umbilical cords with a common insertion about 5 cm from the margin of the placenta. The larger cord was approximately 10 mm in diameter and had three vessels. The smaller cord was approximately 6 mm in diameter and had two vessels. Note the congested appearance of the placental tissue and the vessels on the left and the pallor of the pla-cental tissue and the vessels on the right. (Klima, T.)

Figure 2.34. The twin with the dominant heart of the same pregnancy often shows additional anomalies such as limb reduction defects. These have been attributed to em-bolic disease consequent upon stasis in the acardiac fetus. This twin had some limb anomalies which included fusion of digits of the left hand as seen in this figure.

Dicephalus

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Acardius Anceps

Figure 2.37. This is an example of acardius anceps (hemiacardius). The cranial portion is partially covered by hair, but no head is formed. There is a globular structure of the upper part which shows a rudimentary face with an oral opening through which a cleft palate is seen. Four extremities are present. There is a defect in the anterior abdominal wall with intestinal loops present. (Klima, T.)

Figure 2.37. This is an example of acardius anceps (hemiacardius). The cranial portion is partially covered by hair, but no head is formed. There is a globular structure of the upper part which shows a rudimentary face with an oral opening through which a cleft palate is seen. Four extremities are present. There is a defect in the anterior abdominal wall with intestinal loops present. (Klima, T.)

Neonatal Bowel Loops
Figure 2.38. Close-up of the same infant shown in Figure 2.37. The anterior wall of the abdomen is missing and the intestinal loops are exposed. There is no umbilical cord identified. (Klima, T.)

CONJOINED TWINS

Conjoined twins are rare, one per 50,000 to 100,000 live births. They result from the failure of the zygote to completely divide. This occurs in approximately 1% of monozygotic twins. The incidence of the types of fusion is as follows: The most common types are thoracopagus twins with an incidence of one per 70,000 live births (73.4%), pygopagus twins (18.8%), ischiopagus twins (5.9%), and the most rare types are the craniopagus twins with an incidence of one per 2,000,000 to 4,000,000 live births (1.7%). Conjoined twinning occurs only in mono-amnionic-monochorionic pregnancies.

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Conjoined Twins Thoracopagus

Figure 2.39. In thoracopagus conjoined twins, note the fusion at the thorax and upper part of the abdomen with a single site of umbilical cord insertion. The posture is typical for thoracopagus conjoined twins in that the heads are hyper-extended and the backs are relatively straight.

Figure 2.40. Radiograph of die conjoined twins shown in Figure 2.39 illustrates the hyperextended heads and the fusion of the thoraces and upper abdomen. On fetal radiograph, the hyperextended fetal heads at the same level were considered almost diagnostic of thoracopagus conjoined twins. With the advent of ultrasonography, the diagnosis should be made more readily.

Thoracopagus Images

Figure 2.41. Another set of thoracopagus conjoined twins showing the typical posture of the hyperextended heads.

Figure 2.42. Thoracopagus conjoined twins showing the fusion from the upper thorax to the midabdomen.

Figure 2.41. Another set of thoracopagus conjoined twins showing the typical posture of the hyperextended heads.

Pics Siamese Twins Breast Feeding

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Conjoined Twins Newborns

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Figure 2.44. This fused umbilical cord section from the same set of thoracopagus conjoined twins shows the presence of four vessels, two arteries and two veins. In the fused umbilical cords seen in conjoined twinning, diere may be from two to seven vessels. (Singer, D.)

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Figure 2.45. This fused umbilical cord section showing three arteries and three veins is another example from conjoined twins. (Singer, D.)

Pygopagus Twins

Figure 2.46. Pygopagus conjoined twins are fused at the buttocks.

Figure 2.47. The same set of pygopagus conjoined twins showing the fused genitalia.

Figure 2.48. Close-up of the fused genitalia in the same set of pygopagus conjoined twins.

Figure 2.47. The same set of pygopagus conjoined twins showing the fused genitalia.

Pygopagus Twins

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Craniopagus Twins Separated
Figure 2.49. The twins shown in Figure 2.46 were successfully separated. This figure shows them prior to discharge from the hospital.

Figure 2.50. Radiograph of a set of omphalopagus twins shows the fusion at the abdominal walls and hence they could be separated.

Figure 2.51. An example of craniopagus conjoined twins.

Vaginal Delivery

Figure 2.52. Note on the left, the vaginal delivery of prosopothoracopagus conjoined twins. On the right, note the twins following delivery. Prosopothoracopagus conjoined twins are twins united in the frontal plane with the fusion extending from the oral region through the thorax and upper abdomen. Diagnosis was not made pre-natally and the twins died at delivery. Note that there are only two upper extremities (dibrachus) and four lower extremities (tetrapus). (Caberra-Meza, G.)

Figure 2.52. Note on the left, the vaginal delivery of prosopothoracopagus conjoined twins. On the right, note the twins following delivery. Prosopothoracopagus conjoined twins are twins united in the frontal plane with the fusion extending from the oral region through the thorax and upper abdomen. Diagnosis was not made pre-natally and the twins died at delivery. Note that there are only two upper extremities (dibrachus) and four lower extremities (tetrapus). (Caberra-Meza, G.)

Syncephalus
Figure 2.53. Cephalothoracopagus conjoined twins. Note the syncephalus.

Figure 2.54. Dicephalus conjoined twins with dicephalus, three upper extremities (tribra-chus), and two lower extremities (dipus). Note the two separate heads and the fused chest.

Figure 2.54. Dicephalus conjoined twins with dicephalus, three upper extremities (tribra-chus), and two lower extremities (dipus). Note the two separate heads and the fused chest.

Dicephalus

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Syncephalus Twins

Figure 2.55. A close-up of the same twins shown in Figure 2.54 demonstrates the third upper extremity extending from the fused shoulders. There were two separate neurologic systems, two separate pulmonary systems, two gastrointestinal systems joining at the jejunum, a single genitourinary system, and conjoined hearts with complex anomalies.

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Figure 2.55. A close-up of the same twins shown in Figure 2.54 demonstrates the third upper extremity extending from the fused shoulders. There were two separate neurologic systems, two separate pulmonary systems, two gastrointestinal systems joining at the jejunum, a single genitourinary system, and conjoined hearts with complex anomalies.

Conjoined Twins Anencephaly
Figure 2.56. Another example of di-cephalus conjoined twins. Note that the head on the left of the figure is normal but that there is anencephaly of the head on the right of the figure.

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Lithop Dion
Figure 2.57. Radiograph of the same conjoined twins showing the normal head on the left of the figure and the anencephalic head on the right of the figure. Note that there are fused vertebral columns with some separation at the lower thorax and upper abdomen and that there is dibrachus.

Figure 2.58. Asymmetric ischiopagus conjoined twins. Note that the twin on the right of the figure, which is attached at the ischia, is an anencephalic parasite with a partial thorax and abdomen and two upper and two lower extremities. The "normal" twin on the left of the figure had gastroschisis, imperforate anus, and rectovaginal fistula. There were two bladders, two kidneys, and two uteri present.

Photo Ischiopagus

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Figure 2.59. Close-up of the anencephalic parasite the above asymmetric ischiopagus conjoined in twins.

Figure 2.60. Radiograph of the asymmetric ischiopagus conjoined twins. Note at the bottom the severely anecephalic twin attached to the "normal" twin who has a large gastroschisis. Each twin has four extremities.

Gastroschisis Pictures

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Dipygus Twins
Figure 2.61. Preoperative (above) and postoperative (below) appearance of the asymmetric ischiopagus conjoined twins shown in Figures 2.58 to 2.60.
Ischiopagus Conjoined Twins

Figure 2.62. Dipygus twins. Recent work has suggested that genes are involved in establishing the body axes, metameric pattern (segmentation genes), and regional specialization (homeotic genes). This raises the possibility that many of the abnormalities of facial duplication in man are not a manifestation of incomplete twinning but may be homeotic malformations. Limb duplication may also be a result of stimulation of homeobox gene expression and thus a well-formed pair of arms and/or legs may be seen emerging.

Figure 2.62. Dipygus twins. Recent work has suggested that genes are involved in establishing the body axes, metameric pattern (segmentation genes), and regional specialization (homeotic genes). This raises the possibility that many of the abnormalities of facial duplication in man are not a manifestation of incomplete twinning but may be homeotic malformations. Limb duplication may also be a result of stimulation of homeobox gene expression and thus a well-formed pair of arms and/or legs may be seen emerging.

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Newborn Asymmetrical Eye Development

Figure 2.63. This infant has a well-developed lower extremity emerging from the chest and has been considered to be an asymmetrical double malformation -heteroadelphia (an underdeveloped parasite attached to a well-developed autosite). With the new concept, this could be an example of a ho-meotic malformation. Also note the large omphalocele.

Omphalocele

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Figure 2.65. Duplication of die right leg and foot. The question again arises as to whedier diis is an asymmetric double monster or a homeotic malformation. (Cabera-Meza, G.)

Figure 2.65. Duplication of die right leg and foot. The question again arises as to whedier diis is an asymmetric double monster or a homeotic malformation. (Cabera-Meza, G.)

Double Genitalia Discordant Twins

Figure 2.66. Discordant twins. The twin on the left is an example of a severe caudal regression syndrome. There was oligohydramnios, renal agenesis, imperforate anus, and lack of external genitalia. The twin on the right is normal. (Cabera-Meza, G.)

Figure 2.66. Discordant twins. The twin on the left is an example of a severe caudal regression syndrome. There was oligohydramnios, renal agenesis, imperforate anus, and lack of external genitalia. The twin on the right is normal. (Cabera-Meza, G.)

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Discordant Twins
Figure 2.67. Another example of discordant twins. The twin on the left is an albino and the twin on the right is normal. This is the second set of discordant twins (one albino and one normal) born to this mother.
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Responses

  • Saku
    How does the discharge look from rectovaginal fistulas?
    6 years ago
  • oskar
    What is imperforate anus?
    6 years ago
  • aatifa omar
    What is twin reversed arterial perfusion?
    6 years ago
  • diana
    How are conjoined twins formed?
    6 years ago
  • DANIEL
    How images are formed in the eye?
    6 years ago
  • carl
    Why does the vaginal bone pains at 32weeks?
    2 years ago
  • oronzo
    What causes this Siamese twin?
    2 years ago
  • alessandra
    Can twins b deliverd at 32weeks?
    7 months ago

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