Multiple Births

Multiple birthsMultiple births

Normally only one fetus is delivered at birth

Definition:Definition:It is delivery of more than one fetus by the end of

the same pregnancy (2,3,4,5,or more).

Types of Multiple birthsTypes of Multiple births

Monozygotic – multiple (typically two) fetuses produced by the splitting of a single zygote

Dizygotic – multiple (typically two) fetuses produced by two zygotes

Polyzygotic – multiple fetuses produced by two or more zygotes

Contd….Contd….

Two offspring – twins Three offspring – triplets Four offspring – quadruplets Five offspring – quintuplets Six offspring – sextuplets Seven offspring – septuplets Eight offspring – octuplets

Twins is a form of multiple birth in which the mother gives birth to two or more offspring from the same pregnancy, either of the same gender (sex), or of the opposite.

Types of twins

1/3 1/3 monozygotimonozygoti

cc100% Identical100% Identical

Dizygotic Dizygotic 2/32/3

Fertilization of two ova by two different sperms

Fertilization of one ovum by one sperm

Incidence Incidence Twins account for about 1% of all pregnancies, 66% dizygotic and 33% monozygotic. The incidence of dizygotic twins varies with

ethnic group maternal age  parity method of conception

The incidence of monozygotic twins is similar in all ethnic groups and does not vary with maternal age or parity, but may be 2–3 times higher following IVF (In Vitro fertilization) procedures.

DIZYGOTIC TWINSDIZYGOTIC TWINS When two eggs are

fertilized by two separate sperm to create two embryos

FRATERNAL TWINS Fraternal twins are

always diamniotic / dichorionic

They never share membranes

Each have a placenta

Twin pregnancy Twin pregnancy

Monozygotic TwinsMonozygotic Twins One egg is fertilized by one

sperm but the zygote divides during early mitosis.

IDENITCAL TWINS They will have the same

exact DNA so they must always be the same gender.

There are several kinds of identical twins…It all depends on the timing of the separation of the fertilized egg.

Early Separation Early Separation (1-4 days after fertilization)(1-4 days after fertilization)

Each embryo will have its own amnion and chorion (diamniotic/dichorionic)

Each embryo will develop its own placenta

Average SeparationAverage Separation(4-8 days after fertilization)(4-8 days after fertilization)

Each embryo will have its own amnion but share a chorion (diamniotic/monochorionic)

This is the most common identical twin arrangement…

Sometimes they share a placenta, sometimes they will each have their own placenta. [Having their own placenta is better…]

Late SeparationLate Separation(8-12 days after fertilization)(8-12 days after fertilization)

The embryos will share both an amnion and a chorion (monoamniotic/monochorionic)

This occurs less that 1% of the time… There are usually complications (unequal

nourishment and cord entanglement) due to the fact that they share membranes – close supervision of a doctor is required

The two babies share a placenta.

Very Late SeparationVery Late Separation(12+ days after fertilization)(12+ days after fertilization)

The embryonic cell mass does not fully separate.. Conjoined twins

1 in very 200 identical twins are conjoined. 40% - 60% will be stillborn; 35% survive less than 24 hours.

EtiologyEtiology Two prominent theories explain the appearance of

conjoined twins, the theory of fusion and the theory of fission.

In the fusion theory, authors propose that the twins join secondary to late embryonic division.

in the fission theory, some authors feel there is instead an absence of complete embryonic division.

Teratodelphic conjoined twinsunited high on the body in the form of a lambda ():

Pelvidelphic Thoracodelphic

Teratodymic conjoined twins

twins united caudally in the form of a Y:

Iniodymic

Thoracodymic

Sternodymic

Types of mono-zygoticTypes of mono-zygotic

DiamnioticDichorionic

Diamniotic

MonochorionicMonoamniotic

MonochorionicConjoined

Determination of Zygosity and Determination of Zygosity and chorionicitychorionicity

Zygosity can only be determined by DNA fingerprinting “ amniocentesis, chorion villus sampling or cordocentesis”

Determination of chorionicity can be performed by ultrasonography and relies on the assessment of fetal gender, number of placentas, and characteristics of the membrane between the two amniotic sacs

Different-sex twins are dizygotic and therefore dichorionic, but in about two-thirds of twin pregnancies the fetuses are of the same sex and these may be either monozygotic or dizygotic

Similarly, if there are two separate placentas the pregnancy is dichorionic, but in the majority of cases the two placentas are adjacent to each other and there are often difficulties in distinguishing between dichorionic-fused and monochorionic placentas.