Superfetation - Pregnancy Within A Pregnancy

Ever heard of a pregnancy within a pregnancy? No, not twins — I am referring to a woman who became pregnant twice, maybe weeks apart. Isn't that supposed to be impossible? Almost. There have only been 10 recorded cases of the phenomenon, dubbed superfetation. And thus, unprotected sex during a woman pregnancy could possibly resulted in another pregnancy.

And the recent case involved Julia Grovenburg, a 31-year-old Arkansas woman. In Grovenburg's case, she became pregnant with a girl (whom they've decided to name Jillian) and a boy (Hudson) two weeks later. The babies have separate due dates — Jillian on Dec. 24, Hudson on Jan. 10.

Dr. Robert Atlas, chairman of the obstetrics and gynecology department at Baltimore's Mercy Hospital, says he's never encountered a case of superfetation during practice. He says such pregnancies occur both when a woman continues ovulating after becoming pregnant and when that second, fertilized egg is able to implant itself in the lining of the womb — two things that wouldn't happen in a normal pregnancy. Typically, hormonal changes prevent further ovulation and thicken the lining of the uterus to preclude a second embryo from attaching. Why did that not happen in this case? No one's really sure.

Despite the rarity of Grovenburg's case, Atlas told TIME the phenomenon shouldn't be cause for concern. Grovenburg's babies should behave much as twins do; in all likelihood the second baby will be born slightly premature when Julia goes into labor for the first time. Since the difference between the two is only two weeks, the second baby will be nearly at full term anyway. Indeed, the last known case of superfetation had a happy ending. In 2007, a British woman gave birth to a boy and a girl conceived three weeks apart, with no undue complications.

What is Superfetation

Superfetation (also spelt superfoetation - see fetus) is the formation of a fetus while another embryo is already present in the uterus, from a different menstrual cycle. When there are two separate instances of fertilisation during the same cycle, it is known as superfecundation.

Superfetation is claimed to be common in some species of animals, but is extremely rare in humans. It can occur only where there are two uteri, or where the menstrual cycle continues through pregnancy.

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 2007, Ame and Lia Herrity, conceived 3 weeks apart, were born in the United Kingdom to Amelia Spence and George Herrity.

In May 2007, Harriet and Thomas Mullineux, also conceived 3 weeks apart, were born in Benfleet, Essex, UK to Charlotte and Matt Mullineux.