A young mother from Brazil never imagined that a routine home pregnancy test would turn her life upside down — twice. Kathleen Nicole Ramos Santos, 24, from Nova Iguaçu in the state of Rio de Janeiro, was already raising a young daughter when she discovered she was pregnant again. But what began as a surprise turned into a medical rarity: a pregnancy within a pregnancy.
Early ultrasound scans revealed a significant size difference between the two fetuses, leading to an unusual diagnosis — one of the twin girls was a full week younger than the other. The medical explanation: superfetation, a rare condition where two embryos are conceived at different times during the same pregnancy.
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Kathleen Nicole Ramos Santos with her 'twin' daughters, conceived a week apart
(Photo: Nicoole Carvalhoo Instagram)
Despite the rarity of her case, the pregnancy progressed without major complications. Still, it was classified as high-risk and required close monitoring and extended rest. At week 33, Kathlen gave birth in a dramatic delivery: one baby was born naturally, the second required an emergency C-section about an hour later due to fetal distress.
Both newborns required several weeks of hospitalization in the NICU before being strong enough to go home. There, reality hit: caring for two premature infants, alongside a toddler, and with little daily support.
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Kathleen Nicole Ramos Santos and her whole family
(Photo: Nicoole Carvalhoo Instagram)
Kathleen delivered the babies in 2021 but only shared her story years later, in December 2025, via a video on social media that quickly went viral, drawing hundreds of thousands of views and astonished reactions. Many said they had never heard of such a possibility. She spoke to reporters this week.
What Is superfetation?
In a typical pregnancy, ovulation ceases once an embryo implants in the uterus. But in very rare cases, ovulation can continue, and if intercourse occurs, a second fertilization may result — leading to two fetuses at different stages of development.
Although both babies are usually delivered at the same time, the age gap can affect birth weight and require heightened medical supervision.
Dr. Udi Argaz, deputy director of Delivery Rooms at Rambam Medical Center, emphasized the rarity of the condition and the difficulty in confirming it. "When one fetus is larger than the other, it doesn’t necessarily mean superfetation. It could simply be natural growth differences or complications like unequal blood flow between twins," he explained.
"There’s currently no medical way to definitively prove if a later ovulation led to a second conception," Argaz said. "Diagnosis is based solely on clinical assessment."
Dr. Udi ArgazPhoto: Rambam Medical CenterHe added that some twin pregnancies begin as such, but one embryo may stop developing early without the mother ever knowing. High-risk monitoring is typically recommended in confirmed twin pregnancies.
The key takeaway, according to Argaz, is the importance of early ultrasound by a specialist to accurately assess the type of twin pregnancy, which is critical for proper management and detecting potential complications.
"At an early stage, the type of pregnancy can be accurately characterized, including the number of placentas and sacs, data of great medical significance," concludes Argaz. "As the pregnancy progresses, the characterization becomes more complex. Accurate diagnosis of the type of twin pregnancy is essential for proper management of the pregnancy, as different types of twin pregnancies may be accompanied by unique complications. Errors in characterization may lead to inappropriate medical management and significant consequences for the course of the pregnancy and the health of the fetuses."
This article was prepared with the assistance of Alchemiq's News Analysis System.