Maternal and Infant Health Program Maternal and Infant Health Program

Phone:
  SLC area: (801) 538-9970

FAX:
  SLC area: (801) 538-9409

Mail:
  Maternal and Infant Health Program
  P.O. Box 142001
  Salt Lake City UT
  84112-2001




Twins, Triplets or More

A “twins or more” pregnancy may also be called a multiple pregnancy or a multiple gestation.  This means that a mother is pregnant with more than one baby at the same time. There are two types of twins:  identical and fraternal. 

How do twins and triplets or more happen?
           
Identical twins happen when one egg is fertilized by one sperm but divides after it is fertilized to produce two unborn babies with the same genes.  As a result, identical twins are always the same sex.  Fraternal twins happen when two eggs, instead of just one, are produced in the woman’s ovaries during the same menstrual cycle.  Both eggs are then fertilized by two different sperm.  The unborn babies may be the same sex (boy/boy or girl/girl) or the opposite sex (boy/girl).  They share about 50% of their genes making them no more genetically related to each other than any other brothers and sisters.  Triplets or greater can be identical or fraternal twins or a mix of individually fertilized eggs and/or identical twins.(1) 

How often due twins and triplets happen?

The number of twins born has varied across time and among cultures.  Twinning rates also vary between fraternal and identical twins.  Identical twins happen worldwide at about 1 out of 250 births.(2)  About one in 50 American births are fraternal twins.(3)  About two thirds of twins are fraternal and the rate varies by race.  In the United States, the highest rate of fraternal twins is among Black women, followed by White and then Asian women.(2) 

What things can increase the chance of a woman having fraternal twins?

The following things may increase the risk of a woman conceiving fraternal twins:(1)

  • Having a history of twins in the mother’s family
  • Being an older mom
  • Having had a higher number of prior births
  • Being a taller mom
  • Being an obese mom
  • Being of African race

Are there risks to the mother or babies with twins, triplets or more?     

A pregnancy with more than one baby is a high-risk pregnancy.  It puts the mother at risk for having serious problems during her pregnancy.  The following can be problems for any mother – but carrying twins or more during pregnancy increases these risks:(2)

  • High blood pressure
  • Anemia (low iron in the mother’s blood)
  • Preterm labor (going into labor before 37 weeks of pregnancy [a normal pregnancy lasts 40 weeks])
  • Breaking her bag of water more than 24 hours before delivery and/or more than two weeks before her due date
  • Severe nausea and vomiting causing dehydration that may require IV fluids
  • The placenta [afterbirth] growing over the opening of her uterus (also known as placenta previa).  This may allow the placenta to deliver before the babies are born.  It can cause severe bleeding in the mother and a loss of oxygen to the babies
  • Too much fluid in her bag of water

The following problems can happen at the birth of any infant but twins or more increases these risks:(2)

  • The mother may need a Cesarean section delivery (delivery through an opening the doctor makes in the mother’s abdomen)
  • The placenta may separate from the wall of the uterus before the infants are delivered.  This can cause a loss of oxygen to the babies
  • The babies in the uterus may not be head down.  This makes delivery very difficult and may require a Cesarean section delivery
  • The babies’ cords may become tangled in the uterus or a cord may deliver in front of the baby.  This pinches off the baby’s umbilical cord and blocks oxygen from reaching the babies in the uterus
  • The mother may get an infection in her uterus after delivery of the babies.

Below are problems that can happen to all babies but those that are born as twins or more have increased risk for:(2)

  • Premature delivery (giving birth 3 or more weeks before the due date)
  • The babies being born at a low birth weight (less than 5 pounds 8 ounces) or at a very low birth weight (less than 3 pounds 5 ounces)
  • Weighing less than most babies born at the same stage of pregnancy even if the babies are born near their due date
  • Twin to twin transfusion4

What is twin to twin transfusion?

Twin to twin transfusion only happens to identical twins who share one placenta (afterbirth).  5% to 38% of identical twins who share one placenta develop twin to twin transfusion.  In those that do, one twin becomes the “donor” twin and the other the “recipient” twin.  Blood from the “donor” twin flows into the “recipient” twin.  As a result, the “donor” twin weighs less; he becomes anemic (low iron in his blood); and has a smaller amount of fluid in the bag of water surrounding him.  However, the “recipient” twin, who is receiving a part of his twin’s blood flow weighs more; may have too much fluid in the bag of water surrounding him; and his blood volume may be too high for his heart to handle.  Whether or not twins with a shared placenta will have twin to twin transfusion and, if they do, how serious the problem will be, depends on how much of the placenta is shared and the number and type of blood vessels they share.  While many twins may do well, twins with moderate to severe twin to twin transfusion may have serious problems or die in the uterus.  They may also be born premature – three weeks or more before their due dates.(4)  

What are the infant death rates for twins and triplets?

In 2006 in the United States, while 11% of babies of single births were born too early, 61% of multiple births ended up being born too early.(2)  Being born too early increases the chance a baby will need costly hospital stays, have long-term health problems or die.  In Utah, from 2004 through 2006, twins were 12 times more likely to die in the first year of life than were babies born as single births and triplets were 34 times more likely to die in the first year of life than babies that were born as single births.(5)

Is the number of twins, triplets and more increasing?

Nationally, since 1970, the number of multiple births due to fraternal twins has been rising.  The cause of this increase may be due to an increasing number of women waiting until later in life to conceive, an increase in obesity and the use of assisted reproductive methods.1  In Utah over the past twenty years (1989 through 2012), the number of twin births has increased from a low of 766 babies born as a twin in 1992 to 1,611 babies born as a twin in 2012.  The number of babies born as triplets from 1989 through 2012 has been as low as 18 babies born as a triplet in 1994 to a high of 80 babies born as a triplet in 2000.  In Utah in 2012, there were 78 babies born alive as a triplet.(6)