When a Twin is not a Twin

Mrs Julia Grovenburg knew she was pregnant with a girl (named Jillian), but while examining her, doctors also found a smaller baby growing alongside the girl. The younger baby is believed to be a boy, and has been named Hudson.

The Grovenburg's physician, Dr M. Muyalert confirmed in a statement that Julia is carrying two babies, but that there was a big difference in size of the two fetuses, which the doctor said is possibly due to superfetation.

Superfetation is extremely rare, but the second conception can occur up to 24 days after the first according to Karen Boyle, a fertility expert at the Greater Baltimore Medical Center, speaking on ABC TV. When that happens the second baby can have problems in lung development. The gap between the Grovenburg's first and second babies is probably short enough to minimize health concerns.

Duke University Medical Center's professor of obstetrics and gynecology, Dr Jeffrey Kuller, told WebMD he is skeptical, but it is possibly a case of superfetation. The phenomenon is so rare there have been only a "handful" of cases in the literature. The hormonal changes in pregnancy normally prevent ovulation, but it is possible.

Another explanation for the discrepancy in size is that one of the twins has a chromosomal defect or other medical problem that stunts its growth, but such a large discrepancy in size is unlikely. If the second baby was much smaller its presence may have been missed in the early examination that located the first baby, Dr Kuller said.

The main issue facing Julia and Todd Grovenburg is the timing of the delivery, which would have to be a compromise that is best for both of the babies. In an interview on an Arkansas TV station (KFSM), Julia Grovenburg said the babies both appeared to be healthy, and will probably be delivered in December. Metabolic and chromosomal studies of the babies after they are born should be able to confirm if the pregnancy is a case of superfetation.

Two confirmed cases of superfetation occurred in 2007 when Lia and Ame Herrity were born in Scotland, and Thomas and Harriet Mullineux were born in Essex. Both cases were pairs of babies conceived three weeks apart.

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