Twins & Triplets – Overview

I’m having twins – how will my pregnancy be different?

Approximately 1-2% of pregnant women have twins, although this number is increasing with the widespread use of IVF.  A twin pregnancy is naturally more complicated than having one baby.  All the common symptoms of pregnancy are more pronounced in women carrying twins, including morning sickness, constipation, tiredness, anaemia, varicose veins and back pain.  In addition, some serious pregnancy complications are more common with twins:

  • Miscarriage
  • Premature delivery
  • Pre-eclampsia / high blood pressure
  • Gestational diabetes
  • Fetal growth problems

Twins & Triplets overview - Dr Colin Walsh

I don’t fully understand the different types of twin pregnancy.  Can you explain them?

Twin pregnancies are classified according to the number of placentas (chorionicity) and the number of fluid sacs (amnionicity).  To determine this, you need an ultrasound scan in the first trimester.  In general terms, the more structures the twins share, the higher the risk.  Think of the placenta as a kitchen and the fluid sac as a bedroom.  If each baby has their own kitchen and own bedroom, there’s less chance for trouble.  If they have to share the same kitchen and bedroom, there’s a much higher chance of trouble.

  • Dichorionic-Diamniotic (DCDA twins) are the commonest type (80% of twins).  Each twin has his/her own sac and his/her own placenta. Most DCDA twins will be ‘non-identical.’
  • Monochorionic-Diamniotic (MCDA twins) are the second most common type (20% of twins).  The twins share a single placenta but each have their own sac.  These twins are ‘identical’ and will be the same sex.
  • Monochorionic-Monoamniotic (MCMA twins) are very rare (<1% of all twins).  These identical twins share both the placenta and the same amniotic sac.

My twins are sharing a placenta – why is this more risky?

Approximately 20% of twins share a single placenta (the medical term is monochorionic, or MC for short).  As well as all the risks of twin pregnancy listed above, MC twins carry an added 10-15% risk of Twin-Twin Transfusion Syndrome (TTTS).  TTTS is a very serious problem, where the twins don’t share the placenta equally.  One twin ends up receiving too much blood, while the other twin doesn’t get enough.  TTTS can only be diagnosed on ultrasound scan, so MC twins should be scanned at least every fortnight from 16 weeks onward. These scans should only be performed by an experienced twin scanner.

What about triplets?

A triplet pregnancy is very rare.  It’s also at very high risk of complications.  Triplets should be cared for by a Maternal-Fetal Medicine specialist.

How I came to have a particular interest in looking after twin pregnancies

During my training as a Maternal-Fetal Medicine specialist, I helped to run a high-risk clinic for monochorionic (MC) twins at the National Maternity Hospital in Dublin.  It was a very busy, centralized clinic where we looked after MC twins from all over Ireland.  We personally performed all the advanced scans for each patient throughout her entire pregnancy, managed any complications that developed, and looked after women during both vaginal and caesarean twin births.

It was fantastic training and experience, which I really enjoyed.  Along the way I also published several papers on twins in international scientific journals.  It was a natural fit for me to keep looking after lots of twins when I came to Australia – first in the Maternal-Fetal Medicine Unit at Royal North Shore Hospital and now in my private practice.