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Superfetation (also spelled superfoetation – see fetus) is the simultaneous occurrence of more than one stage of developing offspring in the same animal. In mammals, it manifests as the formation of an embryo from a different estrous cycle while another embryo or fetus is already present in the uterus. When two separate instances of fertilisation occur during the same menstrual cycle, it is known as superfecundation.

Superfetation is claimed to be common in some species of animals, but is extremely rare in humans. In mammals, it can occur only where there are two uteri, or where the estrous cycle continues through pregnancy. The risk with superfetation in humans is that the second baby is often born prematurely, which can increase its odds of experiencing lung development problems.[1]

In animals[edit]

Animals that have been claimed to be subject to superfetation include rodents (mice and rats), rabbits, farm animals (horses and sheep), marsupials (kangaroos and sugar gliders), and primates (humans). Superfetation has also been clearly demonstrated and is normal for some species of poeciliid fishes.[2]

In humans[edit]

Reports of superfetation occurring long after the first impregnation have often been treated with suspicion, and some have been clearly discredited. Other explanations have been given (and demonstrated) for different levels of development between twins. Artificially induced superfetation has, however, been demonstrated, although only up to a short period after insemination.

In 1926, Herbert T. and Eleanor S. Nelson, conceived two months apart, were born in Westfield, New Jersey, to Alfred and Metha Nelson. Herbert was five months gestation and weighed 2 lbs. 3 oz. and was born first. Eleanor was approximately seven months gestation. Bread tins were pressed into service as incubators, and the children were fed with eyedroppers.

On 1 March 1951, Stephen C. and Jane M. Burdick, conceived two months apart, were born to Dixon C. and Mary K. Burdick at Columbia Hospital for Women in Washington, DC. Stephen, born first, was 9 months gestation and weighed 7.5 lbs. Two minutes later, Jane was born. She was seven months gestation and weighed 3.5 lbs.

In 1956, Barry and Earl Fine, conceived eight weeks apart, were born in Massachusetts, USA to Beverly and Max Fine. Barry, the one conceived later, was born first. Earl, conceived first, was born 9 minutes later.

In 1960, John and Mary Tress of Baltimore MD had what the nurse called twins. She was wrong. Dr Paul C Weinberg of Mt. Sinai hospital delivered the boys, Anthony John and Mark Francis, and realized that Anthony, born five minutes before his brother Mark, looked premature. Immediately, Dr Weinberg did X-rays of the boys' thigh bones and noticed a disparity in bone age. Mark was a full-term baby born five minutes after his two-months premature brother Anthony. Anthony was conceived a full two months after his brother Mark. [3]

In 1977, Lori and Jill Bagley, conceived 5–6 weeks apart, were born in Boston, MA to Linda and Joseph Bagley. Jill, the one conceived later, was born first. Lori, conceived first, was born 4 minutes later. Lori was well over 8 pounds and Jill was under 6. Jill also needed to be incubated for her lungs, but Lori's were fully developed.

In 1989, Marty and Drew DePietro, conceived three weeks apart, were born in Sudbury, Ontario, to Dean DiPietro and Carmen Lafond. They were born three minutes apart; Drew, conceived first, was born first.

In 1992, Evan and Taylor Barth, conceived four weeks apart, were born in Hawaii, USA to Michelle and John Barth. Taylor, the one conceived later, was born first. Evan, conceived first, was born 22 minutes later.

In 2007, Ame and Lia Herrity, conceived three weeks apart, were born in the United Kingdom to Amelia Spence and George Herrity.[4]

In May 2007, Harriet and Thomas Mullineux, also conceived three weeks apart, were born in Benfleet, Essex, to Charlotte and Matt Mullineux.[5]

In 2009, Todd and Julia Grovenburg of Fort Smith, Arkansas, received international media attention for Mrs. Grovenburg's conception of an additional child while already pregnant with a child conceived two and a half weeks earlier. If it were possible to carry both children to term, the birth of the first child would be expected in December 2009, whereas the second child would be due in January 2010.[6][7] Grovenburg's obstetrician reported that cases of superfetation "can only be confirmed after delivery by chromosomal and metabolic studies on the baby."[8] Both healthy babies were delivered through Caesarean section on 2 December 2009.[9]


  1. ^ Jacob, Stephanie (September 2009). "Superfetation Double Pregnancy". AOL Health. Retrieved September 2009. 
  2. ^ FishBase's glossary
  3. ^ {Newsweek Magazine, 31 July. 1961}
  4. ^ "Mother Deliveries Babies Minutes Apart but They are Not Twins!", Medindia, 1 October 2007.
  5. ^ Hale, Beth. "The babies born just a minute apart who AREN'T twins", The Daily Mail, Associated Newspapers, Ltd., 15 January 2008.
  6. ^ ABC News: Arkansas Pregnant Woman Is Pregnant Again.
  7. ^ Allen, Nick. "Pregnant woman conceives second child", The Daily Telegraph, 24 September 2009.
  8. ^ Jacob, Stephanie (September 2009). "Superfetation Double Pregnancy". AOL Health. Retrieved September 2009. 
  9. ^ van Sipma, Ashley (1 July 2011). "I got pregnant while I was already pregnant! Woman gives birth to two babies on the same day but they are NOT twins". MailOnline. MailOnline. Archived from the original on 1 November 2011. Retrieved 1 November 2011. 

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