Multiple Pregnancies

Multiple pregnancies(births)

• When more than one fetus is carried to the term in a single pregnancy, • it is called “multiple pregnancy”. • Common multiples are twins and triplets.

MULTIPLE PREGNANCIES • Higher risks of fetal morbidity and mortality. • Risks increase with increase in number of fetuses. • More common because of ovulation inducing drugs and IVF techniques. • Older females have increased chance. • Women of African descent also have more chances of multiple pregnancy.

Multiple pregnancies in humans are usually delivered before the full term (of 40 weeks) gestation. The average length of multiple pregnancy is around; 36 weeks for twins, 34 weeks for triplets, 32 weeks for quadruplets.

Twins and fetal membranes • Twins originating from two zygotes are dizygotic(DZ) or fraternal twins. • Twins originating from one zygote are monozygotic(MZ) or identical twins. • About 2/3 of twins are DZ. • The frequency of MZ is about the same in all populations. • The rate of DZ twinning increases with maternal age.

What is Hellin’s law?

Hereditary influence • DZ twinning shows a tendency to repeat in families. • If the first born are twins,a repetition of twining is about five times more likely in the next pregnancy.

DZ twins • Formed by the fertilization of two oocytes by different sperms. • Could be of same sex or different sex. • Genetically not alike. • “Womb mates”. • Always have two amnions and two chorions but the chorions and placentas may fuse.

MZ twins • Formed by the fertilization of one oocyte and develop from one zygote. • Are of the same sex,genetically identical and very similar in physical appearance. • Physical differences if any are caused by the environment • (e.g.,anastomosis of placental vessels)

In triplets, all the three babies need not be of the same sex. • It is possible to have a combination of MZ and DZ.

•Example • a triplet may have one fraternal baby from one egg plus identical twins from the other. •This is called “polyzygotic birth”.

MZ twinning • Usually begins in blastocyst stage around the first week and results in the division of the inner cell mass into two embryo blasts. • Each has its own amnion and share a common placenta • (monochorionic –diamniotic twin placenta)

MZ twinning Uncommonly,early separation of blastomeres(during 2-8cell stage)results in MZ twins with two chorions, two amnions and two placentas( which may fuse).

MZ twinning

MZ twinning How identical twins can be formed. A divides at two cell stage (most identical). B: divides at about 5 days, creates mirror image identical twins C: divides around day 9, mirror image twins, but now only one sac (dangerous because cords can become tangled). If division happens after day 10, can create conjoined twins.

MZ twins • Late division of the embryonic disc(during second week) results in MZ twins having one amnion and one chorionic sac. •A monochorionic-monoamniotic twin placenta is associated with a 50%fetal mortality. •Their umbilical vessels are so entangled that it results in cutting off circulation to one or both fetuses.

TTTS(Twin To Twin Transfusion Syndrome) Also sometimes known as 'FFTS' (Feto-Fetal Transfusion Syndrome), and as 'TOPS' (Twin Oligohydramnios-Polyhydramnios Sequence), TTTS is a disease of identical twin fetuses caused by abnormal connecting blood vessels in the twins' placenta. This results in an imbalanced flow of blood from one twin to another. This could be very serious for the survival and health of both twins. Once thought to be extremely rare, TTTS is now believed to affect as many as 1 in 1000.

TTTS(Twin-twin transfusion syndrome) (Unbalanced blood supply)

Acardiac twin

TRAP (Twin Reversed Arterial Perfusion) sequence in MZ

Acardiac twin

If placentas fuse, it is impossible to determine whether the twins are DZ or MZ. One has to wait till The color of the eyes or the finger prints develop to do so. Monochorionic diamnionic twin placenta

zygosity

Single chorion

MZ Single amnion Two amnions Very rare

65%

DZ

rare

Two chorions Fused placentas 25%

Two placentas

40%

60%

10%

superfaetation • Formation of a fetus when there is another fetus already in the uterus (seen only lower animals).

Super fecundation The fertilization of two or more oocytes around the same time by sperms from different men. This is commonly seen in some mammals(cats and dogs). DZ twins with different fathers have been confirmed by genetic markers.

Conjoined (Siamese)twins The developing embryo begins to split into identical twins but stops midway to result in a conjoined fetus.

• 1/50,000 to 1/100,000 are conjoined twins.

.70% are female •75% are still born or die within 24 hours.