A lady in America has discovered she is due to give birth to two babies apparently conceived two-and-a-half weeks apart.
Julia Grovenburg learned of her rare medical condition when she went for an ultrasound scan. It revealed not one but two babies, in different stages of development.
"[When] she said, 'and baby number two has got a healthy little heartbeat,' - I just started gagging," Mrs Grovenburg told broadcaster KFSM-TV in Arkansas. "We feel blessed to have something so rare and as of this point they're perfectly healthy."
"[We were] both in shock," her husband added. "We were trying to put the timelines together and everything. We had known she had had a migraine and been at the hospital and actually had a pregnancy test at the time that one would've been conceived."
Doctors believe Mrs Grovenburg has experienced superfetation: the process of conceiving when already pregnant.
Patrick O'Brien, a consulting obstetrician and spokesman for the Royal College of Obstetricians and Gynaecologists, told Sky News that only one case a year is reported worldwide.
"It's a rare thing because when you conceive, your hormones change dramatically. Those changes stop you ovulating and they stop you conceiving," he said.
"It's hard to be certain sometimes because a woman could be having non-identical twins that are markedly different in size from early in a pregnancy," he added.
Tests will be performed when the babies are born to determine exactly what happened. One baby is due to be born at the end of 2009; the second early in 2010.