Monochorionic monoamniotic (MCMA) triplets are an extremely rare type of triplet pregnancy (1 in 100,000) where all three fetuses share one placenta and one amniotic sac. This occurs when a fertilised egg splits late in its development, leading to only one placenta and amniotic sac for the three babies to share. Sharing a placenta and amniotic sac is the rarest type of triplet pregnancy and carries the highest risk of complications. You will have more frequent antenatal appointments and ultrasounds to monitor the babies' growth and well-being.

The chorionicity (number of placentas) and amnionicity (number of amniotic sacs) of the pregnancy should be diagnosed at your dating scan, between 11+2 and 14+1 weeks of pregnancy.  If your health professional isn’t sure whether the pregnancy is MCMA triplets and there is still doubt in the diagnosis of chorionicity, you should be referred to a fetal medicine specialist without delay, as chorionicity is best determined before14 weeks of gestation. You will then have an individualised plan of care for your pregnancy and birth that will include additional visits to the antenatal clinic and extra growth scans for the babies.

The most common complication in MCMA triplets is Twin Reversed Arterial Perfusion sequence (TRAP sequence). Other potential complications include Twin-to-Twin Transfusion Syndrome (TTTS), Twin Anaemia-Polycythaemia Sequence (TAPS), and Selective Fetal Growth Restriction (sFGR or sIUGR), although these are less common in MCMA triplets than in MCDA triplets. Because the babies are in the same amniotic sac, their umbilical cords can sometimes become tangled, and this means there is sadly a risk of sudden and unpredictable death due to cord accidents.

To help manage these risks, MCMA triplet pregnancies are referred to a tertiary hospital which has expertise in caring for this type of pregnancy. The pregnancy is scanned every two weeks from 16 weeks onwards (more frequently if advised), to check for any indicators of complications that may need monitoring or treating. The frequency of diagnostic monitoring for feto-fetal transfusion syndrome should be increased in the woman's second and third trimester to at least weekly if there are concerns about differences between the babies' amniotic fluid level.  These scans will measure fetal growth and the amount of amniotic fluid, look in detail at the babies’ overall anatomy and development, assess blood flow, any signs of being at risk of preterm birth, and the different sizes of the babies in comparison to each other.

If any complications are identified, your health professional will talk you through the treatment options which vary depending on the type of complications and your specific pregnancy. You can read more about the management of these complications in our booklet, Complications in your pregnancy with twins, triplets and more. You will need to register for free to access this.

As MCMA triplets have higher preterm birth rates and a higher risk of fetal loss, a planned caesarean birth is advised. Timing of the planned caesarean birth is carefully considered by the fetal medicine consultant, taking into account the pregnancy's progression and the potential risks to the babies. Due to the shared placenta and amniotic sac, MCMA pregnancies are considered high-risk, and early caesarean birth is often recommended to minimise complications.

You should be offered steroids before the planned caesarean birth to help mature the babies’ lungs. If you have any concerns about your pregnancy, speak to your health professional who is best placed to advise you.