A 24-year-old woman who had been taking a course of contraceptive pills has found she is expecting identical quads.
Ms Zolfaghary was on a low-dose contraceptive
Soheyla Zolfaghary, from Leeds, was told she was expecting four babies after going for a pregnancy scan, the Daily Mirror newspaper said.
Ms Zolfaghary had been on a low dosage contraceptive pill after giving birth to son Zachary seven months ago.
The Multiple Births Association said natural quads were rare as most were born to mothers on fertility treatment.
Ms Zolfaghary told the Daily Mirror she had gone to Leeds' St James Hospital after a home pregnancy test indicated she was expecting.
"I couldn't imagine what I was being told," she said. "It doesn't feel real to me even now. It's momentous - we're shell-shocked.
The hospital's technician told her and partner Matthew Owens she was expecting not one, but four children.
The foetuses, now 12 weeks old, were formed from the same egg but are now growing in separate sacs in her womb.
Elizabeth Bryan, founder of the Multiple Births Association, told the BBC there were risks in trying to carry multiple babies.
She said many of these multiple embryo pregnancies do not go to term, as doctors have to reduce the number to twins or triplets in order to ensure the health of the mother and to increase the survival chances of the babies.
She said it was "most unusual" for quads to be conceived while the mother was on a contraceptive pill, in this case the low-dose Femulen.
She said if mothers were worried about conceiving while on the pill, they should consult their GPs, but added "it's certainly the first time I've heard of quads being conceived in this way".
Ms Zolfaghary said she considered having an abortion, but had changed her mind. "Part of me feels very special because this is so unusual. And I was just enjoying being a full-time mum to Zach."