Earlier this month, a couple in Australia's family grew by four in a matter of minutes, when they welcomed monozygotic quadruplets via Caesarean section.
Born prematurely at 28 weeks and four days (a gestational time when their lungs, digestive systems, and immune systems are still developing), the identical girls were naturally conceived after one single fertilized egg split into four distinct embryos.
To say this is rare is the understatement of the year.
To say this is rare is the understatement of the year.
When it comes to naturally conceiving monozygotic (identical) quadruplets, we're talking chances that are about 1 in 15 million pregnancies, according to medical experts.
One in 15 million.
That's Go-Buy-a-Lottery-Ticket territory.
Yes, because raising four babies at once is exponentially more expensive, but also because if you can pull off those chances with your pregnancy, it's certainly worth a shot for your bank account.
To be fair, some estimates go "as low" as one in 11 million pregnancies when it comes to conceiving spontaneous identical quads.
And while they have nearly a identical genetic make-up, as they grow, slight differences will emerge, thanks to epigenetic changes (these turn "on" or "off" certain genes without changing the actual DNA sequence, which is why some identical siblings can end up with different medical conditions, even though they're considered identical), conditions in the womb, and postnatal environmental factors, like diet, climate, lifestyle, and emotional attachment.
...naturally conceiving fraternal quadruplets is more common, with the odds sitting around one in 700,000 pregnancies.
On the flip side, naturally conceiving fraternal quadruplets is more common (but, to be clear, is still rare), with the odds sitting around one in 700,000 pregnancies (with some medical estimates reaching as high at one in 729,000).
Fraternal quadruplets could be made up of two pairs of twins (identical or fraternal), triplets plus a singleton, or four single babies after a mother hyperovulates and drops four eggs that all get fertilized in a single cycle.
How fertility treatments impact the chances of conceiving quads
Fertility treatments can drastically increase the odds of conceiving quadruplets, whether they're fraternal or identical quads.
Historically, fertility interventions, whether they're oral fertility drugs, injectable hormones (gonadotropins), modern in vitro fertilization (single embryo), or historical in vitro fertilization (three or more embryos), have been responsible for between 77 and 82 percent of all triplets, quadruplets, and higher-order multiple births.
How Different Fertility Treatments Alter the Odds
| Conception Method | Overall Odds of Multiples (Twins, Triplets, or Quads) | Risk Factor / Mechanism |
|---|---|---|
| Natural Conception | ~3% (Mostly twins; Quads are 1 in 700,000) | Single egg release is standard. |
| Oral Medications (e.g., Clomid, Femara) | ~8% to 10% | Mildly stimulates ovaries to mature two or more eggs. |
| Injectable Hormones (Gonadotropins with IUI) | ~30% | Highly unpredictable; can release a massive wave of eggs. |
| Modern IVF (Single Embryo Transfer) | ~1% to 3% | Safe and controlled; multiples happen via embryo splitting. |
| Historical IVF (Multiple Embryo Transfer) | ~30% or higher | Intentionally transferring 2 to 4+ embryos at once. |
In addition, the in vitro fertilization lab environment (including the freezing-thawing process) can cause embryos to split at a higher rate than natural conception.
An extremely high-risk pregnancy
A monozygotic quadruplet pregnancy is extremely rare (there were only about 72 documented cases of identical quadruplets worldwide as of 2020) and incredibly high-risk because all four babies share one single placenta and run the risk of uneven bloodflow and nutrition.
Because monozygotic quadruplets are so rare and the pregnancies are so high-risk, only a handful of these higher-order multiples are alive at any given time around the world.
Like with twins, when it's time to deliver a set of quadruplets, each newborn is assigned its own team of obstetricians, anesthesiologists, neonatologists, neonatal nurses, and other specialists.
When we had our twins, I remember opening my eyes from a micronap to discover there were about 18 people in the delivery room.
When we had our twins, I remember opening my eyes from a micronap to discover there were about 18 people in the delivery room. When you're welcoming four babies in total, I can only imagine how much more cramped that room would be.
With this particular pregnancy in Australia, they were admitted to hospital once they reached 25 weeks' along to be monitored closely until it was time to deliver the babies.
At a couple of weeks old now, these one-in-15-million babies are all doing quite well and will stay at the neonatal intensive care unit at the Royal Brisbane and Women's Hospital until they reach full term.
Did you have quadruplets or know anyone who did? Were they identical or fraternal? Let us know in the Comments section below or connect with us on Instagram to share your thoughts!
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