Understanding Your Twins: Types, Timing & Monitoring
A guide for expectant parents
The most important detail about your twins is determined by an early ultrasound.
This tells us how your babies share (or don't share) the placenta and sac.
This information guides everything: how often we monitor, when we plan delivery, and what we watch for.
Think of the placenta as the life-support system (it provides food and oxygen).
Think of the amniotic sac as each baby's personal space (the water-filled cushion).
Two separate placentas, two separate sacs
Each baby has their own complete support system. This is the most common type.
| Monitoring | When |
|---|---|
| Growth ultrasounds | Every 3–4 weeks starting at 24 weeks |
| Heart rate monitoring (NST) | Weekly starting at 36 weeks |
Full-term for twins is earlier than singletons.
One shared placenta, two separate sacs
Babies share the placenta but have their own space. Always identical twins.
We monitor more often because shared placentas can develop uneven blood flow.
| Monitoring | When |
|---|---|
| Growth ultrasounds + fluid check | Every 2 weeks starting at 16 weeks |
| Heart rate monitoring (NST) | Weekly starting at 32 weeks |
One shared placenta, one shared sac
Both babies float in the same space. This is rare and needs closer monitoring.
We watch very closely because the umbilical cords can tangle.
| Monitoring | When |
|---|---|
| Frequent ultrasounds | Every 2 weeks for growth |
| Daily monitoring | Often hospitalized from 24–28 weeks onward |
Babies receive lung-maturing steroids before early delivery.
Twin placentas work harder than singleton placentas. They can tire out earlier.
The goal: Deliver when babies are mature enough, but before the placenta becomes less effective.
Your pregnancy type determines the safest window for delivery.
| Twin Type | Ultrasound Schedule | Delivery Week |
|---|---|---|
| Di/Di (2 placentas, 2 sacs) | Every 3–4 weeks from 24 weeks NST weekly from 36 weeks |
37–38 weeks |
| Mo/Di (1 placenta, 2 sacs) | Every 2 weeks from 16 weeks NST weekly from 32 weeks |
36–37 weeks |
| Mo/Mo (1 placenta, 1 sac) | Every 2 weeks Daily monitoring (often inpatient) |
32–34 weeks |
You're not on this journey alone. Our team monitors closely and adjusts the plan as needed.
Every twin pregnancy is unique. The schedule we've outlined is our roadmap.
We'll adjust based on how your babies grow and what we see at each visit.
Your job: Show up, ask questions, and let us know how you're feeling.
Our job: Watch closely, explain everything, and keep your babies safe.