A multiple pregnancy is one in which there is more than one baby in the uterus. Multiple births are a relatively rare phenomena and only about 1 in 36 babies born is a pair of twins. Triplets or multiplets are even rarer. The recent increase in fertility treatments has led to an increase in the incidence of multiple births.

Twins are of two basic types – identical and fraternal or non-identical. Identical twins are formed when one fertilised egg splits into two at some time during early pregnancy. Fraternal twins are born when two separate eggs are fertilised by two separate sperms. Identical twins are also called monozygotic while fraternal twins are known as dizygotic. Fraternal twins usually develop in separate amniotic sacs and have separate placentas. Identical twins share the same amniotic sac but have separate placentas.

Identical twins:
Identical twins are born when the fertilised egg splits into two distinct entities in the early stages of cell division. The DNA and other genetic material is shared by the twins. Identical twins have the same genotype and phenotype which means that they not only have a similar genetic make up but also look similar from the outside. Identical twins are always of the same sex.

Siamese or conjoined twins:
A variation of identical twins, these twins are joined at one or the other body part. This is because of incomplete splitting of the fertilised egg during pregnancy leading to incompletely separated individuals. Siamese twins, like identical twins look alike and are of the same sex. However, conjoined twins are joined at some point in their bodies and may also share some organs. Conjoined twins have been known to be joined from the head, chest, stomach and hips.

Mirror twins:
Another variation of identical twinning, these twins are mirror images of each other. They are extremely rare. Such twins have organs on the opposite sides, for eg., one twin will have the heart on the right side instead of the left and will be opposite handed to the other twin.

Fraternal twins:
The most commonly occurring twins, fraternal twins are no more alike – genetically and phenotypically, than any regular pair of siblings. Fraternal twins are formed when two separate eggs are fertilised by two different sperms. They share only the uterine space and the intra-uterine environment. Fraternals may not be of the same sex and they may also not look alike.

A multiple pregnancy is diagnosed with the help of an ultrasound which is done as a routine procedure. The doctor will check for the presence of two amniotic sacs and separate placentas in case of a multiple pregnancy. The mother’s abdomen may also be larger than usual if she is carrying more than one baby.

Multiple pregnancies usually occur by chance, but the probability may be more in women who have a family history of multiple pregnancies. They also result due to fertility treatments that women undergo to increase the chances of pregnancy. Older mothers are more likely to have multiple births than younger ones. In some cases, certain medication cause more eggs to be released which increases the chances of having a multiple pregnancy.

There are some risks that multiple fetuses may be prone to:

Preterm birth – multiple births usually occur before the full term and may have to be delivered by caesarean section.

Slow intra-uterine growth of the babies due to sharing of all nutrients from the mother

Birth defects

Anaemia

Complications of the amniotic sac, umbilical cord or the placenta

Too much fluid in the amniotic sac

Death of one or more fetuses

The mother may also have to face certain problems in case of a multiple pregnancy. Some of these are:

Excessive weight gain

Conditions like hyperemesis gravidarum

Gestational diabetes

Toxaemia of pregnancy (high blood pressure)

Post partum haemorrhage (excessive bleeding after delivery)

As soon as it is diagnosed that the woman is carrying multiple fetuses, she may be prescribed more rest than normal pregnancies. Extra precaution has to be taken during the pregnancy since the chances of a preterm birth are greatly increased. Also, the babies tend to be smaller than single babies. Frequent tests may be done to ensure the good health of the babies. Dietary modifications may be needed since the pregnant woman needs more nutrition to meet her needs. It should be decided in advance whether the babies would be born vaginally or by a caesarean section. Any complication should be brought to the notice of the doctor.