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Multiple pregnancy

Also known as Twins, Triplets, Multiples, Multifetal gestation. Established at conception; confirmed on first-trimester ultrasound.

Carrying twins, triplets, or more is not a disease. It is a pregnancy with more than one baby, and for many people a joyful surprise. Medically it is also a higher-risk pregnancy, which simply means it needs closer attention. Multiples come with a greater chance of preterm birth, preeclampsia, and, for identical twins sharing a placenta, some specific complications. With specialized prenatal care, more frequent visits, and a thoughtful delivery plan, most multiple pregnancies go well. This page explains how twins and higher multiples happen, what changes in your care, and what to watch for.

Know the warning signs When to call a provider
How common
Twins ~1 in 30 births
Triplets or more are far rarer, about 1 in 1,400 births.
When
Confirmed early
Usually diagnosed on a first-trimester ultrasound, which also checks the placentas.
Urgency
Higher-risk care
Not an emergency, but managed closely; some complications are urgent.
Outlook
Usually good
Most multiples do well with specialized care; preterm birth is common.

Understanding it

What is multiple pregnancy?

A multiple pregnancy means carrying more than one baby: twins most often, sometimes triplets or more. About 3% of US births are twins, roughly 1 in 30, while triplets and higher multiples are much rarer. The rate has climbed over recent decades, driven largely by fertility treatment and by more people having babies at older ages, both of which raise the chance of multiples.

There are two basic kinds of twins, and the difference matters medically. Fraternal (dizygotic) twins come from two separate eggs fertilized by two sperm; they always have their own placentas and are no more alike than any siblings. Identical (monozygotic) twins come from a single fertilized egg that splits; depending on when it splits, they may have separate placentas or, more often, share one. Twins who share a single placenta, called monochorionic, need extra surveillance because they can develop specific complications.

Multiples are called higher-risk because nearly every pregnancy complication is more common with more than one baby. Preterm birth is the big one: more than half of twins, and nearly all triplets, are born before 37 weeks. Preeclampsia is about twice as common, and so are anemia, gestational diabetes, growth problems, and heavier bleeding after birth. Identical twins sharing a placenta can develop twin-to-twin transfusion syndrome, where blood flow between them becomes unbalanced.

None of this is meant to frighten, and most multiple pregnancies end with healthy babies. In practice it means more care: earlier and more frequent ultrasounds, closer monitoring, often low-dose aspirin to lower the preeclampsia risk, and a delivery plan tailored to the type of twins and their positions. The care is more involved precisely because it works, catching and managing issues early.

Symptoms

What are the symptoms?

A multiple pregnancy is confirmed by ultrasound, not by symptoms, though it can come with more pronounced pregnancy symptoms. The signs to act on are those of its complications.

Early signs

  • More intense early pregnancy symptoms, such as marked nausea and vomiting
  • A uterus that measures larger, or grows faster, than expected for your dates
  • Greater fatigue, and a higher chance of anemia
  • Often no distinctive symptoms; frequently a surprise on the first scan

Emergency signs — call 911

  • Signs of preterm labor: regular contractions, pelvic pressure, low backache, or a change in discharge before 37 weeks
  • Signs of preeclampsia: a severe headache, vision changes, upper-belly pain, or sudden swelling
  • Your water breaking, or any vaginal bleeding
  • Reduced fetal movement, keeping in mind it can be harder to tell with two babies
  • For identical twins who share a placenta, rapid belly growth or sudden weight gain, which can signal twin-to-twin transfusion

Why it matters

Risks to you and baby

Preterm birth

The most common complication. More than half of twins and nearly all triplets arrive before 37 weeks, and the typical twin pregnancy lasts about 35 to 36 weeks. Much of the specialized care aims to anticipate and, where possible, delay early delivery.

Preeclampsia and other maternal conditions

Preeclampsia is about twice as common in multiples, and so are gestational diabetes, anemia, and heavier bleeding after birth. Closer monitoring and low-dose aspirin help manage this.

Growth problems

One or both babies may grow slowly, or grow unequally (discordant growth). This is watched with regular growth ultrasounds, more often than in a single pregnancy.

Twin-to-twin transfusion syndrome

Specific to identical twins who share a placenta, this is an imbalance of blood flow between them. It affects a notable minority of shared-placenta twins and is why those pregnancies get extra ultrasound surveillance.

How it's found

How is it diagnosed?

A multiple pregnancy is confirmed by ultrasound, ideally in the first trimester, which also settles the crucial question of whether the babies share a placenta.

First-trimester ultrasound

Confirms the number of babies, dates the pregnancy, and, most importantly, establishes chorionicity: whether the babies have separate placentas or share one. This is most accurate early.

Checking the dividing membrane

Sonographic signs, the twin-peak or lambda sign for separate placentas, and the T sign for a shared one, tell your provider which type of twins you are carrying.

Serial growth ultrasounds

Repeated scans track each baby's growth and, for shared-placenta twins, watch for twin-to-twin transfusion, typically every two weeks from around 16 weeks.

Usually at the first scan. Chorionicity is best determined in the first or early second trimester, and monitoring continues throughout.

Treatment

How is it managed?

Care for multiples is more intensive: more frequent visits and scans, preeclampsia prevention, and a delivery plan matched to the type of twins and their positions.

Treatment paths

You will see your provider and have ultrasounds more often than in a single pregnancy, so growth and any complications are caught early. Low-dose aspirin is usually recommended to lower the preeclampsia risk, since carrying multiples is itself a high-risk factor. Shared-placenta twins get extra surveillance for twin-to-twin transfusion. Good nutrition, iron for anemia, and attention to weight gain are all part of the plan.

Monitoring

More frequent growth scans, blood pressure and urine checks, and, for shared-placenta twins, regular TTTS surveillance are the backbone of care.

Can it recur?

Fraternal twins can run in families and are more likely again with repeat fertility treatment or older age, so a future multiple pregnancy is more likely if those apply. Identical twinning is generally a chance event and not familial.

What you can do

Can it be prevented?

  • Take low-dose aspirin if advised

    Because carrying multiples raises the preeclampsia risk, low-dose aspirin, 81 mg daily started after 12 weeks, is usually recommended to lower it. It is safe in pregnancy.

  • Keep every appointment

    Multiples need more frequent visits and scans. This closer monitoring is what catches preterm labor, growth problems, and, in shared-placenta twins, twin-to-twin transfusion early.

  • Eat well and manage anemia

    Two or more babies raise your needs for iron, folate, and calories. Good nutrition and treating anemia support healthy growth and your own reserves for delivery.

  • Learn the warning signs

    Knowing the signs of preterm labor and preeclampsia lets you act quickly, which matters because both are more common with multiples.

Who is more at risk

Risk factors

Fertility treatment
IVF and ovulation-stimulating medicines are the biggest driver of multiples today, because they can lead to more than one embryo or egg.
Older age
Being older than 30, and especially over 35, raises the chance of releasing more than one egg, increasing the odds of fraternal twins.
Family history of twins
A family history of fraternal twins, on the mother's side, makes multiples more likely, as the tendency to release multiple eggs can be inherited.
Prior multiple pregnancy
Having had fraternal twins before raises the chance of another multiple pregnancy.
Race and body size
Twin rates are highest among Black women and are somewhat higher with taller stature and greater body weight.

Do not wait

When to call your provider or 911

  • Call right away for signs of preterm labor: regular contractions, pelvic pressure, a low backache, or a change in vaginal discharge before 37 weeks.
  • Seek urgent care for signs of preeclampsia: a severe headache, vision changes, upper-belly pain, or sudden swelling of the face and hands.
  • Go in for any vaginal bleeding or if your water breaks.
  • Report reduced fetal movement, and ask how best to track movement with more than one baby.
  • For identical twins who share a placenta, mention rapid belly growth or sudden weight gain, which can signal twin-to-twin transfusion.

Talking to your team

Questions to ask your provider

  • Do my babies share a placenta, and what does that mean for my care?
  • How often will I have visits and growth ultrasounds?
  • Should I take low-dose aspirin to lower my preeclampsia risk?
  • When would you plan to deliver, and can I have a vaginal birth?
  • What signs of preterm labor or preeclampsia should I watch for?
  • How much weight gain and iron do I need carrying multiples?

Keep reading

More on multiple pregnancy

All pregnancy guides articles

Good to Know

Multiple pregnancy FAQs

Common questions about multiple pregnancy, answered.

Why is a twin pregnancy considered higher-risk?

Because nearly every pregnancy complication is more common with more than one baby. Preterm birth is the biggest, affecting more than half of twins, and preeclampsia, gestational diabetes, anemia, growth problems, and heavier bleeding after birth are all more likely. Higher-risk does not mean something will go wrong; it means the pregnancy needs closer care.

What is the difference between identical and fraternal twins?

Fraternal twins come from two separate eggs and always have their own placentas; they are ordinary siblings who happen to share a womb. Identical twins come from one egg that split, and depending on when it split, they may share a placenta or have separate ones. Twins who share a placenta need extra monitoring, which is why the early ultrasound checks this carefully.

Will I deliver early?

Probably somewhat early. The typical twin pregnancy lasts about 35 to 36 weeks rather than 40, and more than half of twins are born before 37 weeks. Uncomplicated separate-placenta twins are usually delivered around 38 weeks, and shared-placenta twins earlier. Triplets and higher almost always come early and by cesarean.

Can I have a vaginal birth with twins?

Often, yes, especially with fraternal (separate-placenta) twins when the first baby is head-down and there are no other reasons for a cesarean. The position of the first twin is the biggest factor. Cesarean is common with twins and is the norm for triplets or more.

What is twin-to-twin transfusion syndrome?

It is a complication specific to identical twins who share a single placenta, in which blood flow through the shared vessels becomes unbalanced, so one twin gets too much and the other too little. It affects a notable minority of shared-placenta twins, which is why those pregnancies get an ultrasound every two weeks from around 16 weeks. It is treatable, often with laser surgery.

Do I need to eat for three?

You do need more, but not simply double. Carrying multiples raises your needs for calories, protein, iron, folate, and calcium, and appropriate weight gain supports the babies' growth. Managing anemia with iron is especially important, as it is more common with multiples.

Why am I being offered aspirin?

Because carrying multiples is itself a high-risk factor for preeclampsia, and a low daily dose of aspirin, begun early in pregnancy, lowers that risk. It is well studied and safe in pregnancy, a simple, effective step your provider recommends because you are carrying more than one baby.

Will I have twins again?

It depends on the type. Fraternal twins can run in families and are more likely again with repeat fertility treatment or older age, so if those apply to you, another multiple pregnancy is more likely. Identical twinning is generally a chance event and does not tend to repeat or run in families.

Medically Reviewed · Updated

Reviewed by Dr. Grace Lin, MD, FACOG · OB-GYN

Obstetrician-gynecologist focused on reproductive and sexual health for women: pregnancy, BV, yeast, trichomoniasis and HPV/cervical screening. Our editorial guidelines →

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