Is your MFM your BBFF?

Is your MFM your BBFF? Let’s see how an easy memory trick can help you remember the treatments you need every 2 weeks for twins.

MFM? BBFF? Let’s start with the basics.

Updated 29 Sept 2020. You’ve just found out you’re having monochorionic twins, and that’s awesome. So you might be googling identical twins, and coming up with a lot of different information, and some contradictions. And a LOT of jargon. We want to make things simple and easy to remember for you.

Is Your MFM Your BBFF? The simple way to remember the testing you need.

We all have a BFF right? A Best Friend Forever. Someone who has your back, never tells you a lie, they follow the rules of friendship, and they take care of you, and don’t let you down.

We think it’s important to have a similar kind of relationship with the person in charge of your pregnancy. A Best BEST Friend For pregnancy, so to speak. Someone who’s going to follow the rules for you, take care of you, tell you everything you need to know, and support you through it all.

Introducing your MFM.

Every monochorionic twin pregnancy needs to be referred to a Maternal-Fetal Medicine (MFM) Specialist, or as they’re known in some places, Perinatologists. Most guidelines across the world agree this should be around 16 weeks, so it’s important that you advocate for this. (You can see the guidelines here from NICE & ISUOG as examples)

Your MFM-BBFF should check you at least every 2 weeks, but don’t panic, some may want to check you a little more closely than that even without complications. It’s more important that your new BBFF gets all the information they need to properly care for you.

Why every 2 weeks? Here’s the evidence.

“Uncomplicated monochorionic twins should have a first-trimester scan and be scanned every 2 weeks after 16 weeks in order to detect TTTS and TAPS in a timely manner. Complicated monochorionic twins should be scanned more frequently, depending on the condition and its severity”

Khalil A, Rodgers M, Baschat A, Bhide A, Gratacos E, Hecher K, Kilby MD, Lewi L, Nicolaides KH, Oepkes D, Raine-Fenning N, Reed K, Salomon LJ, Sotiriadis A, Thilaganathan B, Ville Y. ISUOG Practice Guidelines: role of ultrasound in twin pregnancy. Ultrasound Obstet Gynecol 2016; 47: 247–263.

“A scheme of fortnightly ultrasound scans from 16 weeks onward detects 9 out of ten TTTS pregnancies in time.”

Couck I, Ponnet S, Thewissen L, Russo F, Deprest J, De Catte L, Devlieger R, Lewi L. The Detection, Outcome, and Presentation of Twin-Twin Transfusion Syndrome in Monochorionic Diamniotic Twin Pregnancies Followed with a Protocol of Fortnightly Ultrasound Examination. Fetal Diagn Ther. 2021;48(5):353-360. doi: 10.1159/000514575. Epub 2021 Apr 6. PMID: 33823525.

“One of the biggest challenges will be the implementation and uniformization of routine MCA-PSV measurements into the biweekly ultrasound exams for monochorionic twins to timely reach the diagnosis.”

Tollenaar, Lisanne S.A.1,∗; Lopriore, Enrico2; Oepkes, Dick1; Haak, Monique C.1; Klumper, Frans J.C.M.1; Middeldorp, Johanna M.1; Klink, Jeanine M.M. Van2; Slaghekke, Femke1. Twin Anemia Polycythemia Sequence: Knowledge and Insights After 15 Years of Research. Maternal-Fetal Medicine: January 2021 – Volume 3 – Issue 1 – p 33-41
doi: 10.1097/FM9.0000000000000065

“Near-universal recommendation was found for bi-weekly ultrasounds beginning around gestational week 16”

Nicholas, Lauren, Rebecca Fischbein, Stephanie Ernst-Milner, and Roshni Wani. 2021. “Review of International Clinical Guidelines Related to Prenatal Screening during Monochorionic Pregnancies” Journal of Clinical Medicine 10, no. 5: 1128.

twins taps ttts twin anemia polycythemia sequence syndrome support foundation
Congratulations! It’s twins – but what comes next?

So what tests do I need?

This is where your BBFF comes in handy. We use this as our reminder for what tests actually need to be done. Every 2 weeks, your MFM should be checking the following:


At every appointment, they should be doing Doppler readings on the middle cerebral artery (MCA) What this does is check the speed blood is going through the brain – if it’s moving too fast, that’s a sign of anemia, and if it’s moving too slow, it’s a sign of polycythemia. Your MFM-BBFF should be recording these, as this is a reliable indicator for TAPS (as well as some other complications.)


Every appointment it should be checked that both babies’ bladders are visible. Filling and emptying can take a long time to do, so it’s rarely done. Instead, it should be noted what the status of the bladder is (empty/full/normal/enlarged, etc) because there are no actual measurements. A completely empty bladder is rare though, and if the fluid is also low for that twin, this should signal more checks.
Bladders are a huge part of diagnosing TTTS, so it’s important to check them properly.


Another big part of a TTTS diagnosis is fluid levels. Your MFM-BBFF should be checking the deepest, or max vertical pocket (DVP/MVP) of fluid on both babies and recording this in centimeters. Amniotic Fluid Index (AFI) isn’t accurate for monochorionic twins. If one baby’s fluid is below 2 centimeters and the other above 8, then this is a sign of TTTS.


Umbilical arteries (UA) Dopplers are just as important as MCA Dopplers. They’re an insight into the health of the two sides of your placenta. They help with detecting  SFGR and monitoring its progress. The MFM-BBFF should be establishing how many blood vessels are present in each cord, and how the cords insert into the placenta. This can be in the center, on the edge, or even inserted in the membranes. This may have an effect on the growth of the babies. 

MFM BBFF Taps support twin anaemia polycythemia sequence twins ttts siugr
We’re not going to be mad if you right-click and download this to share on your favorite social media!

And there you have it – it’s as simple as that

Brain – Bladder – Fluid – Flow.

BBFF – easy to remember.

Recording this information

It’s really important that your MFM-BBFF records all this information at every appointment. We also suggest writing it down yourself and getting a copy of your records. That way you can also keep track of it all. (Hint: we have a record sheet you can use here!)

You’re looking for the following things on your report:

  • MCA-PSV (or some will record it as MCA PS or Vmax ) – a reading in centimeters/second, or sometimes as an MoM (brain)
  • Visible bladders with their status noted.
  • DVP / MVP – a reading in centimeters (fluid levels)
  • UA-PI – a number on the page, and the words normal, absent, reversed, intermittent (flow)

We know how overwhelming this type of pregnancy can be – so we wanted to make this as simple and transparent as possible. Your MFM can be a great resource and a definite BBFF if you get all the right testing done, and they watch you closely.

But just like in real life – if your BBFF does the wrong thing by you, or doesn’t tell you the truth, or give you all the information you need – maybe it’s time to find a new BBFF 😉

And don’t forget – it’s as simple as Brain, Bladder, Fluid, Flow. That’s all you need to remember!

Want more information? Email us at, or if you’ve been diagnosed with TAPS, or want more information, join our active Facebook group.

Information updated as of 29/09/2020. Many thanks to Prof. Dr. Dick Oepkes who took the time to fact-check and verify the details on this page. We are very, very grateful for your time.

Further updated on 25/02/2021 – shiny new updated video inserted and fact-check performed.