Superfetation: Can You Get Pregnant While Pregnant?

Yes, it’s possible—but it’s extremely rare.
save article
profile picture of Kristen Bringe
Published June 11, 2024
happy pregnant couple at home
Image: Monkey Business Images | Shutterstock

Just when you thought your early-pregnancy worry list couldn’t get any longer, enter: superfetation, or the possibility of getting pregnant while already pregnant. Superfetation is an extraordinarily rare, but it is technically possible. Panicking already? Rest assured that the odds of having “superfetation twins” are extremely slim. That said, it’s pretty fascinating stuff!) Read on to find out all there is to know about the incredibly mind-boggling phenomenon that is superfetation.

Can You Get Pregnant While Pregnant?

Getting pregnant while already pregnant, also known as superfetation, is incredibly rare, but possible. There are different possible scenarios for how this remarkable phenomenon can occur. Kelli Burroughs, MD, ob-gyn and department chair at Memorial Hermann Sugar Land Hospital in Sugar Land, Texas, describes one: “Typically, after a woman conceives, the body naturally stops ovulating. In very rare cases, ovulation continues after a woman becomes pregnant.” A second scenario is that, in some cases, two eggs can be released during ovulation, which would normally result in a typical fraternal twin pregnancy. However, in the case of superfetation, the second egg essentially hibernates and then implants much later than the first.

What Is Superfetation?

In short, superfetation is an exceedingly rare event that “occurs when an egg is ovulated and fertilized, and the resulting embryo implants during an ongoing pregnancy,” says Sasha Andrews, MD, a board-certified maternal-fetal medicine specialist at Pediatrix Medical Group in Denver.

Superfetation vs. twins

Superfetation is different from a twin pregnancy because of the timing of fertilization. With a twin pregnancy, both eggs are fertilized at the same time, while in superfetation, there’s a gap between when the first egg and second egg are fertilized. Andrews elaborates, “This is different than a twin pregnancy in that twins are conceived at the same time, either from a fertilized egg that splits (identical twins) or from two eggs that are fertilized at once (fraternal twins).”

Related Video

Superfetation vs. superfecundation

Superfetation involves two embryos that form during two separate menstrual cycles, per Cleveland Clinic. Superfecundation—an even rarer occurrence—happens when sperm from separate acts of intercourse (and possibly even from separate partners) reach two separate eggs during the same ovulation period.

How Common Is Superfetation?

Superfetation is so rare that the chances of it happening to you are practically nonexistent. In a March 2024 case report, researchers listed that there have been only 14 documented cases in recorded history. However, the odds of superfetation are growing ever so slightly higher in modern times. According to Andrews, “it’s becoming more common with assisted reproductive technologies such as in vitro fertilization.” In fact, in a 2010 case report, researchers asserted that most superfetation cases have occurred after assisted reproductive technologies.

Are There Symptoms of Superfetation?

“There are no unique symptoms of a superfetation pregnancy,” says Burroughs. “Patients may experience no symptoms at all or typical symptoms of pregnancy including nausea, breast tenderness and weight gain.”

How Is Superfetation Diagnosed?

Superfetation is challenging to diagnose in early pregnancy because the symptoms can appear the same as any other pregnancy, and it’s so rare that it’s not something doctors routinely check for. Andrews illustrates a scenario in which atypical symptoms would be present: “Some cases of superfetation have resulted in a heterotopic pregnancy, where one embryo implants within the uterus, and the other is an ectopic pregnancy within the fallopian tube. In these cases, symptoms such as abdominal pain or vaginal bleeding can occur.” Ectopic pregnancies aren’t ever viable.

Burroughs explains what would be required for a superfetation diagnosis: “Diagnosis of superfetation would include review of the menstrual cycle history and an ultrasound. The most common presentation of a superfetation pregnancy is confirmation of a pregnancy followed by confirmation of an additional pregnancy, on a different date, with significant size difference.”

What Are the Risks of Superfetation?

Cases of superfetation that result in ectopic pregnancy are particularly risky and “can result in life-threatening bleeding, requiring blood transfusion or surgery,” says Andrews.

There are also risks if both fetuses are within the uterus. Burroughs explains that superfetation “can lead to asynchronous growth of the fetuses during pregnancy. This means that while one baby may be fully developed and ready for birth, the other may still be in an earlier stage of development, putting the younger fetus at risk of premature birth.” Additionally, any twin pregnancy is more likely to lead to preterm birth, says Andrews.

Preterm birth can cause a host of issues for baby, including “difficulties with breathing, low birth weight, challenges with movement and coordination, feeding difficulties and serious complications such as brain hemorrhage and neonatal respiratory distress syndrome, which is a breathing disorder stemming from underdeveloped lungs,” says Burroughs.

Superfetation occurs so rarely that it’s probably not something you really need to have on your radar. However, if you got pregnant with the help of assisted reproductive technologies such as in vitro fertilization (IVF) and your mama senses tell you something’s amiss, it might be worth bringing up superfetation to your healthcare provider. Or, on the very, very off chance that one of your ultrasounds reveals one more fetus than there used to be, you’ll know what to suspect.

Please note: The Bump and the materials and information it contains are not intended to, and do not constitute, medical or other health advice or diagnosis and should not be used as such. You should always consult with a qualified physician or health professional about your specific circumstances.


Sasha Andrews, MD, is a board-certified maternal-fetal medicine specialist at Pediatrix Medical Group in Denver. She received her medical degree from Baylor College of Medicine.

Kelli Burroughs, MD, is an ob-gyn and department chair at Memorial Hermann Sugar Land Hospital in Sugar Land, Texas. She received her medical degree from Medical University of South Carolina.

Ultrasound in Obstetrics & Gynecology, Spontaneous Superfetation Diagnosed in the First Trimester with Successful Outcome, December 2002

Cleveland Clinic, Superfetation, January 2023

Ginekologia Polska, Superfecundation in Etiology of Twin Pregnancy, October 2006

Clinical Case Reports, Superfetation and Heterotopic Pregnancy: Case Report of Two Rare Phenomena Coexisting and Implications in the Era of Assisted Reproductive Technologies, March 2024

Reproductive BioMedicine Online, Superfetation After Ovulation Induction and Intrauterine Insemination Performed During an Unknown Ectopic Pregnancy, 2010

Learn how we ensure the accuracy of our content through our editorial and medical review process.

save article

Next on Your Reading List

pregnant woman in labor and delivery
Epidurals Could Decrease Severe Birth Complications by 35%, Study Says
By Wyndi Kappes
Kourtney Kardashian and Travis Barker attend the 75th Primetime Emmy Awards at Peacock Theater on January 15, 2024 in Los Angeles, California
Kourtney Kardashian Opens Up About Fetal Surgery That Saved Her Baby
By Wyndi Kappes
optimistic mother with baby on bed
How Birth Trauma Made Me Stronger
Medically Reviewed by Kendra Segura, MD
krystal anderson dead after stillbirth
Kansas City Chiefs Cheer Alum Krystal Anderson Dies After Stillbirth
By Wyndi Kappes
pregnant woman being checked by doctor
Study Suggests US Maternal Mortality Lower Than Previously Estimated
By Wyndi Kappes
Everything You Need to Know About Cholestasis of Pregnancy
Everything You Need to Know About Cholestasis of Pregnancy
Medically Reviewed by Kendra Segura, MD
close up of varicose veins on woman's thigh
Why Some Moms Get Varicose Veins in Pregnancy—and What to Do About It
Medically Reviewed by Kendra Segura, MD
mom holding newborn baby in hospital after delivery
What It Means to Have a Retained Placenta
Medically Reviewed by Kendra Segura, MD
pregnant woman with son
Pregnant After 35: What to Know About Advanced Maternal Age
Medically Reviewed by Kendra Segura, MD
black pregnant woman sitting on doctor exam table
How Pain Inequities Impact Black Women in Pregnancy and Beyond
Medically Reviewed by Kendra Segura, MD
pregnant woman getting blood pressure measured by doctor
What You Need to Know About Preeclampsia
Medically Reviewed by Kendra Segura, MD
pregnant woman getting an ultrasound
What Cervical Insufficiency Means for Pregnancy
Medically Reviewed by Kendra Segura, MD
pregnant woman resting in bed
What Is Bed Rest During Pregnancy—and Is It Recommended?
Medically Reviewed by Kendra Segura, MD
gynecologist performing an ultrasound on pregnant woman
What to Know About a Subchorionic Hemorrhage in Pregnancy
Medically Reviewed by Kendra Segura, MD
pregnant woman sitting on exam table while talking to doctor
What to Know About Placental Abruption
Medically Reviewed by Kendra Segura, MD
doctor doing a blood test for pregnant woman
Simple Blood Test Could Identify Those at Risk of Preeclampsia
By Wyndi Kappes
woman holding newborn baby in hospital bed after birth
In-Hospital Maternal Mortality Rates Have Declined by Over 50 Percent
By Wyndi Kappes
pregnant woman drinking a glass of milk
Drinking Milk Can Lower Your Risk of Pregnancy Complications, Study Finds
Medically Reviewed by Kendra Segura, MD
nuchal cord wrapping around baby's neck in utero
Nuchal Cord: Causes, Signs and Treatment
Medically Reviewed by Kendra Segura, MD
bindi irwin endometriosis diagnosis
Bindi Irwin on Endometriosis and Questions Around Growing Her Family
By Wyndi Kappes
Article removed.
Article removed.
Name added. View Your List