A twin or multiple pregnancy happens either when a single fertilized egg splits into two or more embryos (identical, or “monozygotic”) or when two or more separate eggs are each fertilized by separate sperm (fraternal, or “dizygotic”). The type matters because it affects how many placentas and amniotic sacs the babies share, which in turn shapes how closely your care team will want to monitor the pregnancy. Multiples of any kind need more frequent prenatal visits than a single-baby pregnancy, because the risk of certain complications goes up when more than one baby is developing at the same time.
Seek Care Right Away If You Notice These Signs
Multiple pregnancies carry a higher chance of preterm labor and other complications, so it helps to know the warning signs early. Contact your health care provider immediately, or go to the nearest emergency room, if you notice any of the following:
- Regular contractions, cramping, or a tightening feeling before 37 weeks
- Vaginal bleeding or a sudden gush or steady trickle of fluid
- Pelvic pressure or lower back pain that comes and goes
- A severe headache, vision changes, or sudden swelling of the face or hands
- Sudden pain just below the ribs
- A noticeable decrease in one or both babies’ movements
If you are having a medical emergency, call 911 or go to the nearest emergency room.
Identical vs. Fraternal: What’s Actually Different
Fraternal twins come from two separate eggs and two separate sperm, so they are genetically no more alike than any other siblings — they can be different sexes and always have their own separate placenta and amniotic sac. Identical twins come from a single fertilized egg that splits, so they share the same genetic material and are almost always the same sex. What identical twins share physically inside the uterus depends on how early or late the split happened.
Comparing the Main Types of Twin Pregnancy
- Dichorionic, diamniotic (two placentas, two sacs): Always the case for fraternal twins. Can also happen with identical twins if the egg splits very early. Generally considered the lowest-risk twin arrangement because each baby has an independent blood supply.
- Monochorionic, diamniotic (one shared placenta, two separate sacs): Only happens with identical twins, when the split occurs a bit later. Because the babies share a placenta, this type needs closer monitoring for uneven blood flow between the twins.
- Monochorionic, monoamniotic (one shared placenta, one shared sac): A rarer, higher-risk identical-twin arrangement where both babies are in the same amniotic sac. This type requires the closest monitoring of all twin pregnancies.
Your care team typically determines which type you have using an early ultrasound, since the markers used to tell the types apart are easiest to see in the first trimester and can become harder to identify as the pregnancy progresses.
Why Multiple Pregnancies Need More Frequent Monitoring
Carrying more than one baby raises the overall workload on your body and the placenta or placentas, so your provider will likely schedule visits and ultrasounds more often than they would for a single-baby pregnancy. The exact schedule depends on your specific type of multiple pregnancy, your health history, and how the pregnancy is progressing, so it’s best set by your own obstetric team rather than a general rule. Reasons for closer monitoring include:
- Checking that each baby is growing at a healthy, even rate
- Watching for twin-to-twin transfusion syndrome (TTTS) in monochorionic twins, a condition where blood flow between babies who share a placenta becomes unbalanced
- Screening for preeclampsia, which occurs more often in multiple pregnancies
- Screening for gestational diabetes
- Tracking the position of each baby as the pregnancy progresses, since this affects delivery planning
Complications That Are More Common With Multiples
Not every multiple pregnancy develops complications, but the chances of the following are higher than in a single-baby pregnancy:
- Preterm birth and low birth weight
- Preeclampsia (high blood pressure with signs of organ strain)
- Gestational diabetes
- Anemia
- Uneven growth between babies
- Twin-to-twin transfusion syndrome, specific to monochorionic twins
Some people are also advised to reduce activity later in a multiple pregnancy to help delay labor, though this isn’t needed in every case. Ask your provider whether it applies to you.
What to check before acting on Twin and Multiple Pregnancy
- Ask your provider to confirm chorionicity (shared vs. separate placenta) as early as possible, ideally in the first trimester.
- Ask how often you’ll need prenatal visits and ultrasounds based on your specific type of multiple pregnancy.
- Ask which warning signs should prompt you to call between visits.
- Ask whether you should expect a referral to a maternal-fetal medicine specialist, which is common for monochorionic twins or triplets and higher-order multiples.
- Start talking with your provider about delivery planning in the second trimester, even though the plan may change as the pregnancy goes on.
How Delivery Planning Differs From a Singleton Pregnancy
Delivery planning for multiples takes into account more variables than a single-baby pregnancy does. Your care team will generally consider:
- Each baby’s position: Whether each baby is head-down, breech, or sideways affects whether a vaginal delivery is an option and how it would be managed.
- Chorionicity and amnionicity: Monochorionic and especially monoamniotic twins are usually delivered earlier than dichorionic twins, and your provider will set a personalized target based on your specific situation rather than a fixed date.
- Number of babies: Triplet and higher-order pregnancies are more likely to be delivered by cesarean than twin pregnancies.
- How the pregnancy has progressed: Any complications that come up, like growth differences between babies or preeclampsia, can change the delivery plan.
Because there are more variables to weigh, it’s common for the delivery plan to be revisited more than once as the pregnancy continues. Ask your provider when they expect to finalize a plan and what could change it.
Questions studies have not settled about Twin and Multiple Pregnancy
Monochorionic monoamniotic twins are the highest-risk type of twin pregnancy and are generally managed by a maternal-fetal medicine specialist with more intensive monitoring than other twin types. Triplet and higher-order pregnancies, which are more often the result of fertility treatment, carry higher risks than twin pregnancies across nearly every category, including preterm birth. People carrying multiples after fertility treatment may also be managing other health considerations from that treatment, which is worth discussing with both their fertility specialist and obstetric provider.
This article is a general overview and does not cover every possible complication, every combination of chorionicity and amnionicity, or personalized monitoring schedules and delivery timing, which vary by provider, hospital, and the specifics of each pregnancy.
Common questions about Twin and Multiple Pregnancy
Can identical twins be different sexes?
This is extremely rare. Identical twins come from the same fertilized egg and typically share the same sex chromosomes, so they are almost always the same sex. Different-sex twins are fraternal in the vast majority of cases.
Do all twin pregnancies need a maternal-fetal medicine specialist?
Not necessarily. Many dichorionic (two-placenta) twin pregnancies are managed by a regular obstetric provider. Monochorionic twins, monoamniotic twins, and higher-order multiples are more likely to involve a maternal-fetal medicine specialist because of their higher complication risk. Ask your provider what’s recommended for your specific pregnancy.
Is it possible to have a vaginal delivery with twins?
Sometimes, yes. It depends mainly on the position of each baby, gestational age, and whether any complications have developed. Your provider will discuss what’s realistic for your specific pregnancy as you get closer to delivery.
Does carrying twins always mean an earlier due date?
Multiple pregnancies are more likely to end in preterm birth, and planned delivery is often scheduled somewhat earlier than for a single-baby pregnancy, but the specific timing depends on chorionicity, how the pregnancy is progressing, and your provider’s assessment. There isn’t one standard due date that applies to every multiple pregnancy.
Related Reading
- Pregnancy & Preconception: Getting Ready, Before and After a Positive Test — for context on early pregnancy basics before a multiples diagnosis.
- Fertility & Fertility Evaluation — since fertility treatment raises the chance of a multiple pregnancy.
- Preparing for a Reproductive Health Visit — for tips on getting the most out of frequent prenatal appointments.
- Read our full Medical Disclaimer
Educational Disclaimer
This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. It does not diagnose your pregnancy type, recommend a specific monitoring schedule, or set a delivery plan for any individual. Reading this page does not create a provider-patient relationship. Always consult a qualified health care provider, and a maternal-fetal medicine specialist when recommended, about your specific pregnancy. If you are having a medical emergency, call 911 or go to the nearest emergency room.