Multiples in pregnancy

Twins triplets quads identical and fraternal


Types of Multiples in pregnancy

A pregnancy of two or more fetuses is called a multiple pregnancy. Multiple fetuses can be the same (identical) or different (fraternal). Identical twins or triplets come from a single egg that has been fertilized by one sperm. For unknown reasons, the fertilized egg splits into two or more embryos during the first stage of development. Fraternal multiples come from multiple fertilized eggs.

Some identical multiples share the same placenta. However, they usually grow within separate amniotic sacs in the uterus. In rare cases, identical multiples share one amniotic sac. Fraternal fetuses have separate placentas and amniotic sacs.

Identical multiples:Fraternal
  • Are always the same sex and blood type.
  • Do not always look exactly alike.
  • One may be right-handed while the other is left-handed.
  • They are not related to your age, race, or family history of twins.
Fraternal multiples:
  • Can be of different sexes and have different blood types.
  • May look very different from one another, with different colored hair and eyes.
  • They may also look alike, as siblings often do.
  • Fraternal multiples tend to run in families.


Types of Twins

Fraternal Twins

With fraternal twins, the most common type, the mother contributes two eggs that are independently fertilized in the womb by two different sperm cells from the father. They are genetically as similar as any ordinary siblings. Fraternal twins are simply brothers and/or sisters who happen to be the same age. Fraternals are more common for older mothers, with rates doubling over the age of 35.

Identical twins

Identical Twins

With identical twins, one egg from the mother is fertilized by one sperm from the father, and then very early in development the embryo splits and two fetuses grow. These twins are very similar genetically and they are the same gender. Identical twins appears to be a random event, not a hereditary trait, and is uniformly distributed in all populations around the world.

More information on Twins in pregnancy.

Semi Identical Twins
The 'semi-identical' twins are the result of two sperm cells fusing with a single egg, before becoming two embryos. This would result in a set of twins with identical genes from the mother's side, but different ones from the father's side. An embryo created this way doesn't usually survive, but a few cases are known.



How Common are Multiples?

There has been an increase in multiple births in recent years. Since 1980, infertility treatment has more than doubled the American twin birth rate. The rate of triplet or more births is now nearly 5 times higher than before infertility treatment was used.multiple pregnancies

In the year 2000, in the United States, there were:
  • 118,920 Twin Births
  • 6,740 Triplet Births
  • 507 Quadruplet Births
  • 78 Quintuplets & other higher order Births
That is more than a 70 percent increase in the number of twin births from 1980. With just over 4 million births in the United States in 2000, about 3% of babies born in the United States are twins or higher order multiple births (such as triplets), which although not common, does mean that multiples are more common than many people believe.

What are your chance of having more than one baby at a time?

Basically, it is about 3% or 1 in 33. The chance of having 'natural' fraternal twins is only about 1.7% or 1 in 60. The chance of having identical twins has remained steady, and is about 0.4% or 1 in 250. The chances of having twins with the use of fertility treatments can be as high as 20 to 25%.
  • chance of having 'natural' fraternal twins: 1 in 60
  • chance of having 'natural' identical twins: 1 in 250
  • chance of having 'fertility treatment' multiple: 1 in 4
  • chance of having 'natural' triplets: 1 in 8,100 (only about 30% of triplets are 'natural')
  • chance of having 'natural' quads: 1 in 729,000 (only about 6% of quads are 'natural')
  • chance of having 'natural' quints: 1 in 55,000,000
Common factors that increase the chances of conceiving twins.
  • Fertility Drugs: Taking fertility drugs or undergoing fertility treatments can significantly increase your chances of having twins or another type of multiple birth. In some cases, it can increase your chances of having twins by more than 20%.
  • Age: Your chances of having twins increases as you grow older. The chance of having twins rises to 4% between the ages of 30 and 34, and to 5% between the ages of 35 and 39.
  • Family History: Having a maternal history of twins or other multiple births increases your chance of becoming pregnant with twins considerably.
  • Cultural Background: People of African American descent are more likely to have twins or multiple births. People of Asian or Hispanic descent are less likely to have twins.
  • Previous Pregnancies: Women who have had four or more previous pregnancies are the most likely to have twins.


Higher Risks with Multiples

What risks?
If you are expecting twins, you will be classed as a high risk pregnancy. Extra demands are placed on the mother and the placental system on which the babies rely. This may slow the growth of one or both the babies, and cause high blood pressure in the mother. There is a strong chance of premature birth. These risks are made greater with triplets or higher multiple pregnancies.

Your doctor may suggest an early scan if you look large for your due date or have a history of multiples in yor family, but you will most likely find out at your first routine scan, 12 to 14 weeks. On rare occasions, the second baby is missed in an earlier scan as it is hidden behind the first.

Nearly all multiple pregnancies are now diagnosed in the first trimester by ultrasound. However, some twins die and are absorbed in the first half of pregnancy ('the disappearing twin' syndrome) and early scanning increases awareness of this phenomenon.

Being told you are expecting twins or more can be a shock, particulary if you have no family history of twins. You will get more antenatal care, and you will need to take more care of yourself than if you were having one baby, but there is no reson to consider youself invalid.

Making sure that you have enough rest and eat a healthy diet are important to your body as it has to work harder. Most likely you will not go the whole term, so you may have to leave work earlier than planned, if you have other children, try to arrange for help so you don't get overtired.




Although a naturally occurring phenomena, multiple pregnancies are considered high-risk because:

  • Smaller babies - fetuses tend to be individually smaller than those in a singleton pregnancy because of greater demand for nutrients and slower in utero growth i.e. light-for-dates. Monozygotic twins tend to be smaller than dizygotic twins.
  • Increased risk of prematurity - the mean gestation for twins is 37 weeks and for triplets 31 weeks.
  • Higher risk of congenital abnormality associated with multiple pregnancies (x2 rate in singleton pregnancies).
  • Higher rates of cerebral palsy found in twins (1 - 1.5%) and triplets (7 - 8%).
  • Perinatal mortality (at 22 completed weeks gestation and over) rate for twins is significantly higher than singletons (x5) and even higher for triplets (x6). Rates are higher for monochorionic twins than dichorionic twins (49 versus 11.5 in 1000).
  • Higher rate of maternal pregnancy-related complications such as hyperemesis gravidarum (from Greek hyper and emesis and Latin gravida; meaning " excessive vomiting of pregnant women"), polyhydramnios (an abnormally large volume of amniotic fluid), pre-eclampsia, anaemia, antepartum haemorrhage.
  • Higher rate of complications in labour - malpresentation, vasa praevia, cord prolapse, premature separation of placenta, cord entanglement, postpartum haemorrhage.

Complications of multiple pregnancy do not end with birth. Language and speech delay, more general cognitive delay or motor problems, behavioural problems and difficulty in parent-child interactions all appear to be more common in multiple birth children. Also the non-medical financial, social and emotional consequences of caring for twins or higher order multiples need to be kept in mind.