Multiple pregnancies

• Definition

Pregnancies resulting in the birth of more than one neonate at a time are graded as multiple pregnancies.

• Types of multiple pregnancies

• Multiple pregnancies may be

–mono-ovular (identical) or

–poly-ovular (fraternal)

• Mono-ovular multiple pregnancies result from fertilization of a single ovum that will later on split into two.

• They are also called mono-zygotic type of multiple pregnancies.

• The embryos, fetuses and neonates resulting from a mono-zygotic pregnancy are called mono-zygotic (Identical) twins.

• In other words twins resulting from one zygote are mono-zygotic twins.

• These twins will share 100% same DNA,

• They have the same hand and footprints and

• Yet have different teeth marks and fingerprints.

• Poly-ovular multiple pregnancies result from fertilization of more than one secondary oocyte.

• They are usually di-zygotic type of multiple pregnancies.

• But it may be tri-zygotic type, tetra-zygotic and so on.

• Dizygotic twins come from two different secondary oocytes, each fertilized by two different sperms.

• That mean they share only 50% of their DNA, much like all other singleton siblings.

• They can be the same or opposite sexes.

• They can as dissimilar as some singleton siblings.

• But

• They can look like identical twins, very rarely.

• The embryos, fetuses and infants resulting from a di-zygotic pregnancy are called di-zygotic twins.

• In other words twins resulting from two zygotes are di-zygotic twins.

• They are also called fraternal twins.

• They are almost two third of twin pregnancies.

• The frequency of di-zygotic twins shows marked racial differences

• but

• The incidence of monozygotic twins is almost the same in all populations.

• The frequency of di-zygotic twins increases with maternal age

• but

• The incidence of monozygotic twins is not affected with maternal age.

• The fetal membranes and placentas vary according to the origin of the twins.

• When more than two fetuses co-exist,

• they may come from one secondary oocyte or

• May come from more than one secondary oocyte or

• be the result of combined mono-ovular and poly-ovular twining.

• About 25% of identical twins are mirror image twins.

• Their hair falls in opposite directions,

• They have mirror image fingerprints

• If one is right handed, the other is left handed.

• Half identical twins occur when one secondary oocyte splits into two ootids before fertilization.

• Each ootid is then fertilized by a separate sperm.

• These twins share 75% of their DNA as they share the same DNA from ootids and different DNA from each sperm.

• The incidence of multiple pregnancies has increased in these days due to excessive use of exogenous gonadotrophins.

• These drugs are given to women with ovulatory failure who are treated for infertility.

• Conjoined ("Siamese") twins are those that are attached at birth.

Craniopagus Thoraco-abdominopagus

Pyopagus

• Conjoined twins can be separated from each other if they have no vital parts in common.

• For example in craniopagus if the brain tissue is common it will be very difficult to separate the conjoined twins.

• But if the two brains are separate and only the skull cavities communicate it will be easy to separate the two babies from each other.

• Multiple pregnancies have higher risks of fetal morbidity and mortality than single pregnancies

• Morbidity:

• Morbid means diseased or unhealthy.

• Morbidity is the condition of being diseased.

• It is the sick rate.

• It is the ratio of sick to well persons in a community.

• Mortality:

• Mortal means subject to death or destined to die.

• Mortality is the quality of being mortal or the death rate.

• The fetal morbidity and mortality progressively increases as the number of fetuses increases.

• Study of twins is important in human genetics. It is useful for comparing the effects of genes and environments on the development of insan (human being)

• Are there signs that determine whether a woman is more likely to have twins? Yes.

1. Women who are of above average height and who have a large bone structure are more likely to have twins.

2. Women who give birth at an older age (30+)

3. Women who have taken fertility drugs 4. Women who have been on birth control

for several years. 5. Women who were fraternal twins

themselves, the chances of their having twins increase fivefold.

Di-zygotic twins

• Poly-ovular multiple pregnancies result from fertilization of more than one secondary oocyte.

• They are usually di-zygotic type of multiple pregnancies.

• But it may be tri-zygotic type, tetra-zygotic and so on.

• The embryos, fetuses and infants resulting from a di-zygotic pregnancy are called di-zygotic twins.

• In other words twins resulting from two zygotes are di-zygotic twins.

• Di-zygotic twins result from simultaneous shedding of two secondary oocytes and fertilization by two different sperms.

• The resulting two zygotes have totally different genetic constitutions.

• They share only 50% of their DNA, much like all other singleton siblings.

• They can be the same or opposite sexes.

• The infants born are not identical to each other.

• They may be two brothers or two sisters or one sister and one brother.

• So they have no more resemblance than any other sisters or brothers born at different times.

• The only thing they have in common is that they were in their mother’s uterus at the same time.

• They were womb-mates.

• They are also called fraternal (brotherly) twins.

• The two zygotes implant independently. They have their own placentae, amnions and chorionic sacs.

• In approximately 40% cases the implantation of two zygotes is very close; the two placentas are thus so close that they may fuse together.

• Similarly the walls of the chorionic sacs may also appose each other and fuse.

• Occasionally, di-zygotic twins posses red blood cells of two different types, indicating that the fusion of two placentas was so close that red blood cells were exchanged.

• This is called erythrocyte mosaicism.

• The incidence of di-zygotic twins is 7 to 11 per thousand births.

• Approximately two-thirds of twins are di-zygotic twins.

• Di-zygotic twins show hereditary tendency.

• The tendency of di-zygotic twins to repeat in families is evidence of hereditary influence.

• This is a photograph of Mr Liaqat with his two dizygotic twin daughters. They are sitting in the lap of their father. Saba Liaqat is on right side (the side of her grandmother) and Ayesha Liaqat is on left side.

• Saba Liaqat is blackish while Ayesh is whitish in color. Ayesha was born half hour before Saba.

• A photograph of dizygotic sisters, Saba and Ayesha. Both are five year old in this photograph. Saba is one and half inch taller than Ayesha.

• The incidence rate of di-zygotic twins increases with maternal age.

• The frequency of di-zygotic twins shows marked racial differences.

• Asians 1 in 500.

• Caucasians 1 in 125.

• Africans 1 in 20.

• The recurrence risk in families is about three times than in general population.

• If the first born are di-zygotic twins, the chances of twining or some other form of multiple births are approximately five times more in next pregnancy than in general population.

• Studies show that the genotype of mother affects the frequency of di-zygotic twins, but the genotype of father has no effect on the frequency of di-zygotic twins.

• Genotype: The entire genetic constitution of an individual.

• Two secondary oocytes.

• Two blastocysts have developed from two zygotes.

• Each blastocyst implant separately. Each has its own placenta, amniotic cavity and chorionic cavity

• The two blastocysts may implant like Ayat 9 i.e. both with cephalic presentation.

• They may implant like Ayat 10 i.e. one with cephalic presentation and other with breach presentation.

• Note in Ayat 9 and 10 placentas, chorions and amnions are separate.

• The two blastocysts may implant like Ayat 11 i.e. both with cephalic presentation.

• They may implant like Ayat 12 i.e. one with cephalic presentation and other with breach presentation.

• Note in Ayat 11 and 12 the two placentas and chorionic sacs are fused but the amnions are separate.

Mono-Zygotic Twins

• Mono-ovular multiple pregnancies result from fertilization of a single ovum. They are also called mono-zygotic type of multiple pregnancies.

• The embryos, fetuses and infants resulting from a mono-zygotic pregnancy are called mono-zygotic twins. In other words twins resulting from one zygote are mono-zygotic twins.

• Mono-zygotic twins are always of the same sex. They will be either two sisters or two brothers.

• They are genetically identical and very similar in external appearance.

• If they are exposed to similar environments they produce similar results.

• Physical differences between mono-zygotic twins are environmentally induced.

• I remember my two female students in Army medical college.

• Now Dr Ayeshah and Dr Javairiah.

• They were mono-zygotic twins.

• Their handwriting was very similar.

• They used to secure almost equal marks.

• They result from splitting of the zygote at various stages of development.

• The earliest separation is believed to occur at two to eight cell stages.

• Here the zygote splits and form two separate identical zygotes.

• They develop into two morulas and then into two blastocysts.

• The two blastocysts implant separately.

• Each developing embryo has its own placenta and chorionic sac.

• Although the arrangement of membranes and placentas of these twins resembles the membranes and placentas of di-zygotic twins yet these twins can be recognized as partners of a mono-zygotic pair by their strong resemblance in blood groups, fingerprints, eye color, hair color, and external appearance.

• And they are always of the same sex.

• ALLAH may split the developing zygote at early blastocyst stage, around the end of first week.

• The embryoblast is divided into two groups of cells, resulting in two embryoblasts within the same blastocyst cavity.

• The two developing embryos have a single common placenta and single common chorionic cavity but separate amniotic cavities.

• The placenta is called monochorionic-diamniotic twin placenta.

• In rare cases the separation occurs at bilaminar disc stage, before the appearance of primitive streak.

• In this case the two developing embryos have a single common placenta, a single common chorionic sac and a single common amniotic sac. Although the twins share a single common placenta yet the blood supply is usually well balanced.

• The incidence of mono-zygotic twins is 3 to 4 per thousand births.

• The type of membranes and placentas formed depends on when the twining process started.

Separation

Two Cell Stage

Splitting of Zygote

Early Blastocyst Stage

Bilaminar Germ Disc Stage

• Saim and Sarim are two brothers.

• They are monozygotic twins.

• They were born on 2000.

• They are sons of Dr Sadia Rasheed.

• Look at the two pictures.

• Look at the identical response Saim and Sarim in both pictures.

• Saim and Sarim driving magic car.

• Observations of Dr Sadia (the mother of Saim and Sarim) regarding her monozygotic twins

• If one suffers from fever, the other monozygotic brother is bound to get fever.

• Once a louse was found in the head of Saim.

• I checked the head of Sarim and found similar louse their also.

• Both have similar handwriting.

• But their behaviors are quite different from each other.

• Look at the picture

• Saim and Sarim came to me along with their mother.

• I presented two bottles of cola for them.

• Sarim immediately took the bottle but Saim did not. He took rooh afza from his bottle and drank it.

• He was afraid of cough but Sarim was not in spite of the instructions from his mother.

• Dr Sadia says

• Saim is sober, never fight.

• Sarim is aggressive, always beats Saim.

• If there is one toffee Saim will not take it, Sarim will take it.

• If father says, “I will beat you”. Saim becomes afraid but Sarim not.