About Your Pregnancy

What Type of Twins Are You Having?

You are pregnant with identical twins — a truly special pregnancy that benefits from close, expert monitoring.

Medical Term: Monochorionic Diamniotic (MCDA)

Monochorionic — your twins share one placenta, the organ that nourishes both babies.

Diamniotic — each baby has their own protective fluid sac and their own personal space.

1 in 3

identical twin pairs share a placenta

~70%

of MCDA pregnancies remain complication-free

Shared blood vessels connect the twins through the placenta — which is why we monitor closely every two weeks.

Why We Monitor Closely

Why Do You Need Extra Monitoring?

Shared blood vessels don't always divide flow perfectly evenly. Close surveillance lets us catch imbalances before they become serious problems.

What We Watch For

Unequal fluid levels around each baby
A significant size difference between the twins
Unusual blood flow patterns on Doppler ultrasound
Signs of anemia in one baby while the other has too-thick blood

The good news: We can detect all of these conditions on ultrasound — often weeks before they become serious — giving us real time to act.

Your Care Plan

Your Monitoring Schedule

Ultrasound Every 2 Weeks

Starting around 16 weeks, we see you every two weeks for a detailed scan — continuing until delivery.

What We Check at Each Visit

Fluid levels around each baby (amniotic fluid index)
Estimated weight of each baby and the percent size difference between them
Doppler blood flow in the umbilical artery, middle cerebral artery, and ductus venosus
Bladder filling — confirms kidneys are working properly
Cervical length — early warning of preterm labor risk
Fetal heart rates and biophysical profile scores

Every appointment matters. Two weeks is the ideal interval — long enough for changes to develop, short enough that we can catch them early.

Conditions We Monitor

The Three Main Conditions We Watch For

Twin-to-Twin Transfusion Syndrome (TTTS)

Blood shifts from one twin ("donor") to the other ("recipient"), shown by unequal fluid levels and bladder sizes. Laser therapy is highly effective when caught early.

Selective Fetal Growth Restriction (sFGR)

One twin grows slower due to unequal placental sharing. We use Doppler blood flow patterns to classify severity (Type I, II, or III) — this directly guides the safest delivery timing.

Twin Anemia-Polycythemia Sequence (TAPS)

One twin becomes anemic while the other has too many red blood cells. Detected by measuring brain blood velocity (MCA-PSV Doppler).

Remember: You currently have none of these conditions. We check regularly because early detection makes all the difference.

Today's Visit

Your Ultrasound Today: Great News!

Both babies are growing well with normal estimated weights
Both babies have normal, reassuring heart rates
Fluid levels are balanced around both babies
Doppler blood flow is normal in both umbilical arteries
Your cervix is a healthy length — low risk of early delivery
No signs of TTTS, sFGR, or TAPS today

Baby Size Comparison

Twin A
Normal growth

Twin B
Normal growth

Size difference is within the normal range — this is excellent!

Next appointment: In 2 weeks for your next detailed ultrasound.

Baby Size & Growth

Understanding Size Differences Between Twins

Because twins share a placenta, one baby sometimes receives a larger share. We measure the estimated weight discordance — the percent size difference between the two twins.

Normal

< 20% difference

Routine every-2-week monitoring continues

Mild Concern

20–25% difference

Increased surveillance; Doppler assessed closely

Significant

> 25% difference

sFGR likely; delivery timing guided by Doppler type

Severe

> 30% difference

High risk; individualized plan, possible hospitalization

Key point: Size alone doesn't determine timing. We combine the size difference with Doppler blood flow to make the safest delivery decision.

Delivery Planning

When Will You Deliver? — The Big Picture

For uncomplicated MCDA twins, delivery is planned earlier than a singleton because the shared placenta carries a small but real risk of sudden complications in the final weeks.

SMFM / ACOG Recommendation

36 – 37

weeks gestation for uncomplicated MCDA twins

By 36 weeks, babies' lungs are mature. This timing balances the risk of continuing the pregnancy against the risks of prematurity.

If a complication develops — such as growth restriction or abnormal Doppler — delivery timing shifts earlier. The next slides explain exactly how.

Growth Restriction & Delivery

Delivery Timing When One Baby Is Smaller

When selective growth restriction (sFGR) is present, we classify it by the umbilical artery Doppler pattern of the smaller twin. Each type carries a different risk and a different optimal delivery window.

Type

Doppler Pattern

Deliver

I Low EFW

Umbilical artery Doppler Positive end-diastolic flow — blood moves forward normally through the cord. Generally favorable prognosis.

34–37weeks

II High Risk

Umbilical artery Doppler Persistently absent or reversed EDF — blood struggles to reach baby. Risk of sudden, unpredicted loss of the smaller twin.

30–32weeks

III Variable

Umbilical artery Doppler Intermittently absent or reversed EDF — flow fluctuates unpredictably. Requires very close, frequent surveillance.

32–34weeks

Classification: Gratacos et al. Exact timing individualized with your MFM team based on full clinical picture.

Doppler Ultrasound

What Doppler Findings Mean for Delivery

Doppler ultrasound measures how blood flows through specific vessels. These three measurements guide us most when planning delivery:

Vessel Measured

What It Tells Us

Plan / Timing

Umbilical ArteryNormal forward flow

Good placental function; baby receiving adequate blood supply

Routine monitoring; target 36–37 wks

Umbilical ArteryAbsent end-diastolic flow

High placental resistance; baby working harder to get blood

Intensify surveillance; likely deliver 30–34 wks

Umbilical ArteryReversed end-diastolic flow

Severe placental insufficiency; delivery usually within days

Urgent management; often deliver ≤ 32 wks

MCA-PSV (Brain)Elevated > 1.5 MoM

Baby anemic — heart pumping faster to compensate; suspect TAPS or TTTS

Confirm TAPS; individualize delivery plan

Ductus VenosusAbsent or reversed A-wave

Severe cardiac strain; late but critical warning sign

Delivery usually within 24–48 hours

Delivery Summary

Your Delivery Timing at a Glance

Uncomplicated MCDA

36–37 wks

Normal growth and Doppler throughout

sFGR Type I

34–37 wks

Small baby, normal forward cord flow

sFGR Type III

32–34 wks

Intermittent absent/reversed flow

sFGR Type II

30–32 wks

Persistent absent or reversed flow

TTTS (post-laser)

34–36 wks

After successful laser treatment

DV reversed A-wave

≤ 32 wks

Emergency cardiac compromise

Your current plan: Because everything looks normal today, we are targeting 36–37 weeks. If anything changes, we will explain the new plan right away.

Safety

When to Call Your Doctor

Contact Your Care Team Right Away If You Notice:

Vaginal bleeding of any amount
Fluid leaking from your vagina
Severe or persistent abdominal pain
Regular cramping or contractions (more than 4–6 per hour)
Your belly suddenly looks much larger or tighter
Shortness of breath or difficulty breathing at rest
Decreased or absent movement from either baby

These symptoms don't necessarily mean something is wrong — but they do mean we need to evaluate you promptly.

It is always better to call than to wait and wonder. Your team would rather reassure you than miss something important.

Your Role

How You Can Help Your Babies Thrive

Attend Every Ultrasound Appointment

These every-two-week visits are the single most important step you can take — don't skip them even when you feel completely fine.

Take Prenatal Vitamins Daily

Your body is nourishing two growing babies — it needs consistent extra support.

Stay Well-Nourished and Hydrated

Good nutrition supports healthy growth for both babies. Dehydration can trigger contractions in twin pregnancies.

Rest When Your Body Asks For It

Twin pregnancies are harder work. Adequate rest is medically meaningful — not a luxury.

And always — ask questions. No concern is too small to bring up.

Your Care Team

We're Partners in Your Care

You're doing something remarkable — growing two babies. You deserve a team that communicates clearly and supports you at every step.

Your Support Team

Your OB: Routine prenatal care and overall pregnancy management
Your MFM Team: Detailed ultrasound and Doppler every 2 weeks, complication management
Labor & Delivery: Ready to respond quickly if needed
You: The most important person on the team — your observations and questions matter

We communicate with each other to make sure nothing falls through the cracks. If we see anything concerning, we'll discuss it with you immediately — no surprises.

Today's bottom line: Both babies look great. Doppler is normal. Your delivery target is 36–37 weeks. Keep doing what you're doing! 💙

Summary

Key Takeaways

You have identical (MCDA) twins sharing one placenta
Both babies look great today — normal growth and normal Doppler
Ultrasound every 2 weeks monitors fluid, size, and blood flow
Uncomplicated MCDA twins deliver at 36–37 weeks (SMFM/ACOG)
If size discordance develops, Doppler type guides delivery: Type I → 34–37 wks, Type III → 32–34 wks, Type II → 30–32 wks
Abnormal Doppler (absent/reversed flow, reversed DV A-wave) can trigger urgent delivery
Call right away for bleeding, fluid leaking, reduced movement, or contractions
You are an essential, active member of your care team

Next Steps

Return in 2 weeks · Continue OB prenatal care · Call with any concerns anytime

You've got this! 💙

Your Twin Pregnancy Journey