Twinning Lecture PDF

Unified Lecture 18 HIHD-211 TERM-3 TWINNING Dr Ahmed Aldarmahi Consultant and Associate Professor Basic Science Department COSHP, KSAU-HS, KSA LEARNING OUTCOMES By the end of this lecture the student should be able to: 1. Define twinning 2. Describe dizygotic twin 3. Describe monozygotic twin 4. De...

Unified Lecture 18 HIHD-211 TERM-3 TWINNING Dr Ahmed Aldarmahi Consultant and Associate Professor Basic Science Department COSHP, KSAU-HS, KSA LEARNING OUTCOMES By the end of this lecture the student should be able to: 1. Define twinning 2. Describe dizygotic twin 3. Describe monozygotic twin 4. Describe the arrangement of fetal membrane and placenta in both the types of twin 5. What is conjoined twin, enumerate different types of the conjoined twin The leading country… Saudi Arabia Hsaanah & Husseinah’s case October 2023 3 New case.. Philippines twins just arrived to Riyadh Two days ago.. To KASCH 5-5-2024 4 Twinning ▪ ▪ ▪ LO-1 It is defined as the bearing of two children at one birth. 90% of twins are dizygotic (fraternal) twins… 3-4 per 1000 births are monozygotic (identical) twins. Factors That Increase Twinning 1. Advancing age of the mother – women in their 30s & 40s have higher levels of oestrogen than younger women: their ovaries are stimulated to produce more than 1 egg at a time 2. Number of previous pregnancies – the greater the number of pregnancies a woman had, the higher her conceiving twins 3. Heredity – a woman is more likely to conceive fraternal twins if she is a fraternal twin, has already had fraternal twins, or has siblings who are fraternal twins LO-2,3 Factors That Increase Twinning 4. Race – Black African women have the highest incidence of twins, while Asian women have the lowest 5. Assisted reproductive techniques or IVF – many procedures rely on stimulating the ovaries with fertility drugs (gonadotropins) to produce eggs and, often, several eggs are released per ovulation LO-2,3 Dizygotic Twins LO-2 - Dizygotic twins are created after the ovulation of two oocytes, which are fertilized by two different sperms. - The resulting zygotes are completely genetically different. - Later, each zygote is implanted separately in the uterus. - The developing embryos have their own placenta, amnion and chorion. 9 Placenta and Membranes in Dizygotic Twins ▪ The zygote implants individually at distant sites in the uterus and usually each develop its own placenta, amnion and chorionic sac ▪ Sometimes the two placenta are so close together that they may fuse ▪ The walls of chorionic sac may also fuse if implanted close together LO-4 Erythrocyte Mosaicism in Dizygotic Twins ▪ Occasionally each dizygotic twin possesses red blood cells of two types indicating so close implantation to exchange red blood cells. LO-4 Monozygotic Twins 1. Splitting of one fertilised egg 2. Two babies with exactly the same genetic information LO-3 Monozygotic Twins  Arise by the: 1. subdivision and splitting of a single embryo 2.Splitting of a two-cell embryo 3.Subdivision of the inner cell mass in a blastocyst LO-2,3 subdivision and splitting of a single embryo Cleavage of an early embryo, with each half developing as a completely separate embryo. LO-2,3 Splitting of a two-cell embryo LO-2,3 Subdivision of the inner cell mass in a blastocyst Placenta and Membranes in Monozygotic Twins Splitting At Two Cell Stage Two separate zygotes develop The blastocyst implants separately Each embryo has its own placenta and chorionic sac Although the arrangement of the membranes of these twins resembles that of dizygotic twins, the two can be recognized as partners of a monozygotic pair by their strong resemblance in blood groups, fingerprints, sex and external appearance LO-2,3 Monozygotic Twins results from splitting of zygote at various stages of development Arise by the: 1. Separation at two cell stage, here two separate zygotes develop 2. The inner cell mass splits in to two separate groups of cells within the same blastocyst 3. In rare case the separation occurs at the bilaminar germ disc stage. LO-2,3 There is splitting at the two-cell stage and the embryo has its own placenta, amniotic cavity, and the chorionic cavity. 18 Splitting of the inner cell mass of a blastocyst and the formation of two embryos LO-2,3 Subdivision of the inner cell mass in a blastocyst - The inner cell mass splits in to two separate groups of cells within the same blastocyst resulting in two completely separate group. - The two embryos have a common placenta and common chorionic sac but separate amniotic cavities. 20 In rare case the separation occurs at the bilaminar germ disc stage. The embryos have a common placenta, common amniotic cavity and the common chorionic cavity 21 Monozygotic twins: rarely when separation occurs at bilaminar germ disc stage just before the formation of primitive streak common placenta, and sacs are seen LO-4 Other Types of Multiple Births Triplets may be derived from: One zygote and be identical Two zygotes and consist of identical twins and a singleton Three zygotes and be of the same sex or of different sexes 23 Abnormalities Associated with Twins 60% are born preterm High incidence of low birth rate Infant mortality rate is 3 times higher compared to singletons Only 29% of women pregnant with twins actually give birth to two babies Twin-twin transfusion syndrome: Blood flow to one of the twins is more with poor outcome LO-5 Conjoined Twins  Known as Siamese twins  Identical twins whose bodies are joined in utero  Two embryos take shape, but they are joined by a tissue bridge of varying proportions  The bridging between the twins vary: 1. 2. LO-5 A relatively thin connection in the chest/back Massive fusions along much of the body axis Inner cell mass does not completely separate or if portions of the inner cell mass secondarily rejoin. Conjoined twins LO-5 The Most Common Types Of Conjoined Twins 1. Thoraco-omphalopagus: bodies fused from the upper chest to the lower chest. These twins usually share a heart, and may also share the liver or part of the digestive system 2.Thoracopagus: bodies fused from the upper thorax to lower belly. The heart is always involved in these cases. LO-5 3. Omphalopagus: bodies fused at the lower chest. Unlike thoracopagus, the heart is never involved in these cases; however, the twins often share a liver, digestive system, diaphragm and other organs. 4. Parasitic twins: Twins that are asymmetrically conjoined, resulting in one twin that is small, less formed, and dependent on the larger twin for survival. 5. Craniopagus: Fused skulls, but separate bodies. These twins can be conjoined at the back of the head, the front of the head, or the side of the head, but not on the face or the base of the skull LO-5 OMPHALOPAGUS THANK YOU 29