How Much Twins Can Weigh at Birth: Averages and Extremes

| Reviewed By Amanda Lundberg, BSN, RN

On average, twins are born weighing around 5 1/2 pounds, but it is not unusual for twins to weigh 7 pounds or more each.

Under 5.5 pounds is considered low birth weight, and under 3 pounds, 4 ounces is very low birth weight.

  • Average Weight of Twins at 28 Weeks: Around 2 1/2 pounds
  • Average Weight of Twins at 30 Weeks: Around 3 pounds
  • Average Weight of Twins at 32 Weeks: Close to 4 pounds
  • Average Weight of Twins at 34 Weeks: Around 4 pounds, 10 ounces
  • Average Weight of Twins at 35 Weeks: Almost 5 pounds
  • Average Weight of Twins at 36 Weeks: Slightly over 5 pounds
  • Average Weight of Twins at 38 Weeks: About 6 1/2 pounds

The earlier twins are born, the lower their birth weight will be, and the longer they remain in the womb, the higher their birth weight will be.

However, in most cases, twin babies will weigh less at birth than single-birth babies of the same gestational age, and this may not be a bad thing.

One study showed that:

“The low birth weight of twins may be beneficial to them, since in the United States of America the lowest fetal death rate for twins was observed at an earlier gestational age (36-37 weeks) with a lower birth weight (2500-2800 g).”

Twins Birth Weight

How much your twins will weigh when born depends on various factors.

Your doctor will estimate your babies’ weights throughout the pregnancy through ultrasounds and growth measurements.

This will help you be prepared as you approach labor.

Average Birth Weight for Twins

The average birth weight for twins is 5.5 pounds, but this depends on what type of twins they are and if they share a placenta. 

  • Fraternal twins (dizygotic) develop from two separate fertilized eggs. They can have different genetic backgrounds and can vary significantly in size and weight.
  • Identical twins (monozygotic) develop from a single fertilized egg that splits into two embryos. They tend to be closer in size and weight compared to fraternal twins, but they can still have some variation.

There are other factors that can affect birth weight as well.

The weight of twins at birth can be influenced by factors such as genetics, maternal health, nutrition during pregnancy, and gestational age (whether they are born prematurely or at full term). 

It’s not uncommon for one twin to be larger or smaller than the other, especially in cases of fraternal twins.

Babies born at a low or very low birth weight are at risk for immediate and future complications.

Healthy Weight for Twins at Birth

A healthy weight for twins at birth is 5 1/2 pounds or more each.

Twins can be born weighing more than this, but a minimum of 5 1/2 pounds is the goal.

Fun Fact: In 1027, in Arkansas, a set of twins was born with a combined weight of 27 pounds, 12 ounces! So far, that record holds.

Lowest Viable Birth Rate for Twins

Babies born prematurely before week 22 rarely survive, but some do.

In week 22 and the weeks after, the odds of survival increase incrementally each week the babies remain in the womb. 

Effects of Low Birth Weight

Twins are more likely to be born with low birth weight compared to singletons due to the fact that they have to share the mother’s resources during pregnancy. 

Additionally, twins are more likely to be born prematurely, which increases the likelihood of having a low birth weight.

The effects of low birth weight can vary depending on how severe it is and whether any other complications are present. 

Some potential effects of low birth weight in twins include:

  • Increased risk of health problems: Low birth weight babies, including twins, may be more prone to various health issues, such as respiratory distress syndrome, infections, and developmental delays.
  • Long-term health implications: Low birth weight can have lasting effects on a child’s health and development. It may increase the risk of chronic health conditions, such as heart disease, diabetes, and cognitive impairments later in life.
  • Nutritional needs: Low birth weight infants, including twins, may require specialized feeding and nutritional support to help them grow and develop properly.
  • Developmental delays: Low birth weight babies, especially those born prematurely, may experience developmental delays in areas such as motor skills, language, and cognitive function.
  • Emotional and social challenges: Some studies suggest that low birth weight infants may face a higher risk of emotional and behavioral difficulties as they grow older.

How Birth Weight Relates to Future Size

Birth weight can sometimes predict future size, but this doesn’t always hold true. 

While bigger babies tend to grow up to be bigger adults and babies born with a low birth weight typically have a lower body mass as adults, genetics, nutrition, and overall health play significant roles in determining a child’s ultimate size. 

Birth weight is just one piece of the puzzle.

A new mother and father cradling their newborn twins' feet in their hands.

Factors Affecting Birth Weight

Your babies sharing a womb will affect their birth weight, but there are other factors that impact birth weight as well.

1. Mom’s Health

If you struggle with certain health conditions, like anemia or high blood pressure, your babies are at risk of having a low birth weight.

Diabetes can actually cause your babies to put on too much weight in the womb and be born heavy. 

This is why medical conditions need to be managed well during pregnancy.

Of course, factors like poor nutrition, smoking, and drug use can negatively impact birth weight.

2. Gender

Boys often weigh more than girls at birth, but there are exceptions to this.

3. Age of the Mother

If you are less than 20 years old or more than 35 years old, you are more likely to have babies with a low birth weight.

How Early Twins Can Be Delivered Safely

You can deliver twins as early as 24 weeks, but there will be a long NICU stay for both babies if they are born this early and survive.

Most doctors want to wait until you are at least 34 weeks along before delivering twins.

This isn’t always possible, but the extra time gives their lungs longer to develop and their bodies more time to put on necessary weight.

According to Medscape

“The minimum age of viability is considered to be 23 weeks’ gestation, with scattered reports of survivors born at 21-22 weeks’ estimated gestation.”

Average NICU Stay for Twins

If you have twins, they could be in the NICU for any amount of time depending on when they were born.

The average NICU stay for twins is between 9 days and 25 days.

Babies Born at 8 Months Survival Rate

Babies born at 8 months gestation have over a 95 percent rate of survival.

Is 36 Weeks Full Term for Twins?

While 36 weeks can be considered full-term for twins, most doctors try to wait until 37 weeks to deliver them.

Between 36 and 37 weeks is often considered a safe time depending on what type of twins you’re having and what is going on in the womb.

Carrying Twins to 40 Weeks

It’s not advisable to carry twins to 40 weeks.

The risk of stillbirth and other problems increases, and twins just don’t have the room to grow after around the 37- or 38-week mark.

Twins who are sharing a placenta do not need to be in the womb for a full 40 weeks.

Risks of Carrying Twins Past 38 Weeks

Carrying twins past 38 weeks can be risky, especially if they share a placenta.

Even if the babies have separate placentas, room in the womb runs out faster, and that leads to the possibility of complications.

After 38 weeks, the risk of stillbirth increases, and the benefits of staying in the womb aren’t significant.

How To Reduce the Risk of Twins Having a Low Birth Rate

Reducing the risk of twins having a low birth weight involves a combination of prenatal care, healthy lifestyle choices, and medical monitoring. 

Here are some steps that can be taken to help minimize the risk:

  • Early and Regular Prenatal Care: Early and consistent prenatal care is crucial. This allows healthcare providers to identify and address any potential issues early on.
  • Nutrition: A balanced and nutritious diet is essential. Adequate intake of essential nutrients like folic acid, iron, calcium, and protein is important.
  • Weight Gain: A healthcare provider will provide guidance on appropriate weight gain during pregnancy, depending on the mother’s starting weight and health status.
  • Rest and Stress Management: High levels of stress or inadequate sleep can potentially impact the health of both the mother and the babies.
  • Avoidance of Harmful Substances: Smoking, alcohol, recreational drugs, and certain medications can be harmful to developing fetuses.
  • Monitoring for Complications: Twin pregnancies are considered high-risk, so close monitoring is important.
  • Manage Underlying Health Conditions: If the mother has any pre-existing health conditions (e.g., diabetes, hypertension, etc.), it’s important to manage them under the guidance of a healthcare provider to minimize potential complications.

What Is the Average Time Between Twins Being Born?

The average time between twins being born is around 17-19 minutes.

How Long Do Twins Stay in the Hospital?

If your twins are born without major medical issues or weight problems, they may go home within 3-4 days.

Twins who have to stay in the NICU average between 9-25 days depending on what medical problems they have and how much progress they are making.