Birth Defects in Twins

Babies from twin pregnancies are more likely to suffer from birth-related complications than those from singleton pregnancies. Fraternal and identical twins can be affected by pregnancy complications, and subsequent birth defects.

One of the most common issues is that twins are very often delivered preterm, often due to premature rupture of the membranes. While most mother give birth to healthy babies, there may be problems that lead to improper development of one or both the fetuses. This increases the chance of twins being born with birth defects by 50%.

Birth weight defects

It is common for twins to be a little underweight compared to babies from singleton pregnancies. This is because they are born premature or before the entire pregnancy term is finished. Since a fetus mainly gains weight in the last trimester of pregnancy, in the case of preterm twins the babies do not get the opportunity to gain weight before birth.

Babies will increase in weight soon after birth, but those born before 32 weeks and weighing less than 3.3 pounds are at increased risk for long term problems. Such problems include blindness, hearing loss, mental retardation and cerebral palsy.

Genital and urinary defects

A study conducted by the University of Florida’s Maternal Child Health Education Research and Data Center, found that boys were at a 29% higher risk of developing birth defects in pairs of opposite sex twins.

The boys were two times more likely to be born with defects affecting their genitals and urinary organs than the girls. Researchers believe this is because boys develop at a slower pace in the womb as compared to girls. They believe that if the baby is further ahead in development it would be protected against certain birth defects.

Congenital hip dislocation

The same study by researchers at the University of Florida also found that boys were five times more likely to be born with an obstruction between the stomach and the small intestine. However a common birth defect in twin is congenital hip dislocation. Researchers computed that girls were ten times more likely to end up with congenital hip dislocation than boys.

This condition has an abnormal hip joint wherein the ball at the top of the thigh bone, is not stable within the socket which is supposed to hold it. This often causes the ball and socket joint to dislocate at the time of birth. The ligaments on the hip are stretched or loosened due to this dysplasia.

Twin to twin transfusion syndrome

Identical twins who share a single placenta but have two separate amniotic sacs are called monochorionic twins. The shared placenta connects the blood supply of the twins, allowing the flow of blood between them.

In case there is unequal blood supply, the twins will develop at different rates. This can lead to a condition where the smaller twin pumps blood to the larger twin. It is called twin to twin transfusion syndrome (TTTS).

Gradually the donor twin will have a substantially lower blood supply, leading to anaemia as well as less amniotic fluid. The recipient twin will have an excessive blood supply, leading to excess urine production, bloating of the amniotic sac with too much fluid, and risk of a prenatal form of heart failure. Both twins will be born with birth defects and are very much at risk for being born preterm. If detected in time they may be treated in the womb and should be born healthy.

Twin reversed arterial perfusion (TRAP) sequence

This uncommon condition, also termed Acardiac Twinning, affects less than 1% of monochorionic twin pregnancies. In this condition, one twin develops with an abnormally functioning heart. It may also be missing other organs such as the head or limbs. The acardiac twin receives all its blood supply from the healthy twin as they are sharing umbilical artieres via the placenta.

This places pressure on the healthy twin’s heart, putting it at risk of heart failure and even death. The survival rate for the healthy twin is 25-50% if the TRAP sequence is not treated in time. The condition can be identified by a simple ultrasound and will require prenatal care of the healthy twin to reduce the risk of heart failure. Unfortunately, the acardiac twin will not survive.

Congenital heart defects

Twins are more likely to develop a congenital heart defect than babies from singleton pregnancies. Congenital heart defects are the most common form of birth defect and there has been a have reduced mortality due to them in recent years. The term actually refers to a number of different defects that may affect the heart, which are classified as cyanotic and non-cyanotic.

  1. Cyanotic defects are easily identifiable based on the blue skin colour of the baby caused due to the lack of oxygen.
  2. Non-cyanotic defects may be tougher to identify at birth as they may not have any obvious physical symptoms.

Reviewed by Afsaneh Khetrapal, BSc (Hons)

References

  1. http://www.chw.org/medical-care/fetal-concerns-center/conditions/infant-complications/birth-defects-in-monochorionic-twin/
  2. http://americanpregnancy.org/multiples/vanishing-twin-syndrome/
  3. https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=85&ContentID=P08021
  4. http://americanpregnancy.org/multiples/complications/
  5. http://publish-www-ufl.wcm.osg.ufl.edu/news---archive/archive/2005/11/multiple-birth-babies-boys-have-higher-risk-of-defects.html
  6. http://www.chw.org/medical-care/fetal-concerns-center/conditions/infant-complications/twin-to-twin-transfusion-syndrome/
  7. http://www.chw.org/medical-care/fetal-concerns-center/conditions/infant-complications/trap-sequence/
  8. https://medlineplus.gov/ency/article/001114.htm

Further Reading

Last Updated: Dec 22, 2016

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