In an extremely rare case, a Texas woman became pregnant while already
pregnant and ultimately gave birth to twins who had been conceived roughly
one week apart, according to news reports.
The 30-year-old woman, named Cara Winhold, initially learned she was
pregnant in March 2021, and when she received an ultrasound five weeks
later, there appeared to be just one embryo developing in her uterus, the
Daily Mail reported. However, since Winhold had a history of miscarriages,
her doctor asked that she come in for another scan just two weeks later, to
check that the pregnancy was still progressing well. At that follow-up, not
one, but two implanted embryos popped up on the scan.
"On the very first scan, there was a sac with one baby and then when I went
back there was a really tiny little sac in the corner that had another baby
in it," Winhold told the Daily Mail. "You could see baby A was more
developed, whereas the other one was like a tiny dot."
This rare phenomenon, in which a second pregnancy occurs in the midst of
another pregnancy, is known as "superfetation."
Few cases of superfetation are described in the medical literature, but of
those reported, most have occurred in women undergoing fertility treatments,
such as in vitro fertilization (IVF), according to Healthline. This
procedure involves transferring fertilized embryos into the uterus, and
superfetation may occur if the patient then ovulates and that released egg
gets fertilized in the weeks following the transfer.
In Winhold's case, she had not undergone any fertility treatments, she told
the Daily Mail. Such cases are considered exceptionally rare, in part,
because three unlikely events must happen simultaneously, Live Science
previously reported.
First, an ovary must release another egg, or ovum; this typically doesn't
occur because, at the start of pregnancy, the body releases hormones to halt
ovulation. Second, that egg must be fertilized by a sperm cell; this is
improbable because mucus builds up in the cervical canal in early pregnancy,
forming a "plug" that blocks the passage of sperm. And finally, the
fertilized egg must implant in the uterus. With one embryo already implanted
and developing, there may not be much room for a second. Typically, specific
hormones are released during implantation to help the process along, and
this release wouldn't happen with a pregnancy already underway.
If all these improbable events occur, two pregnancies will ensue at the same
time, but the resulting fetuses will be two different gestational ages,
meaning they'll be at different stages of development. (This differentiates
such twins from fraternal twins, who develop from two fertilized eggs but
are the same gestational age, according to the Live Science report.) Winhold
said that, according to her doctor, "most likely I ovulated twice, released
two eggs, and they got fertilized at different times, about a week apart,"
she told the Daily Mail.
Winhold gave birth to her rare set of twins in October 2021, according to
the Daily Mail. Colson, the baby who was conceived first, was slightly
larger than his twin, Cayden, at birth and still outweighed him at their
six-month checkup.
Originally published on
Live Science.