I’m having twins – why do I need special ultrasound scans?
Women having twins or triplets need more ultrasound scans during their pregnancy. Twins and triplets have a higher risk of complications, so they need to be watched closely.
Ultrasound has revolutionized the modern management of twin pregnancies. With early diagnosis of complications like Twin-Twin Transfusion Syndrome (TTTS) and poor growth, we can time treatments and delivery much better than in the past. Your scans should be performed and interpreted by someone who is very experienced at twin scanning, though; the quality of the scan makes a big difference.
How often should I be scanned?
Ideally, all women with twins should be scanned before 12 weeks, so we can determine the type of twins. All twins also need the standard Early Anatomy (12-14 week) and Morphology (19 week) scans.
First trimester screening for twins is a whole topic on its own! I’ll be posting this as a separate section later in the twins series, so keep an eye out.
The recommend schedule of ongoing scans depends on whether the twins are sharing a placenta or a fluid sac:
- Dichorionic-Diamniotic (DCDA) twins
Each twin has their own sac and own placenta. This is the commonest type of twins (80%). DCDA twins should have regular scans every 3-4 weeks from 24 weeks onwards.
- Monochorionic-Diamniotic (MCDA) twins
MCDA twins share a placenta but have their own sacs. There is a 10-15% risk of Twin-Twin Transfusion Syndrome (TTTS), which is a very serious complication. International best practice is for MCDA twins to be scanned every 2 weeks, commencing from 16 weeks, to watch for TTTS developing.
- Monochorionic-Monoamniotic (MCMA) twins and triplet pregnancies
MCMA twins (who share both a placenta and sac) and triplets are very rare. These pregnancies are very complex and should be managed by an experienced Maternal-Fetal Medicine specialist. The schedule of scans will depend on many factors.