PEE PEE /POO POO ,WHO KNEW?

o unborn babies urinate/defecate in the womb?

18-Aug-2006

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Dear Cecil:

Do unborn babies pee and/or defecate in the womb? --Realtime, via e-mail

Cecil replies:

That's two questions, so two answers. Number one: yes, and it's a good thing they do.
Number two: yes, but you better hope they don't.

Fetal urination is normal. It's part of that "miracle of life" folderol the
nature programs exalt just before they hit you with something you'd rather not know.
Naturally, fetal urine isn't quite the same as yours or mine. It does contain urea, but
much of the nitrogenous waste enters maternal circulation for mama to clean up. Fetal
urine isn't yellow, either. Fetuses and newborns lack enzymes to convert bile pigments to
urobilin, which colors the output of older children and adults.

Urine production begins late in the first trimester, about the same time the two-inch
embryo becomes a fetus. In the second half of pregnancy, fetal urine is an important
constituent of amniotic fluid. By the time the kid is about ready to pop out, he or she is
passing roughly a liter a day. Where does it go? Seems kids learn the benefits of
recycling early on--they swallow it. They'd better, too, lest polyhydramnios (a
potentially dangerous buildup of fluid volume) result. When fetal urination is impaired,
the opposite complication, oligohydramnios, usually occurs.

Fetal defecation isn't normal, but fetuses do accumulate a mass of greenish feces,
called meconium, in their intestines. Unlike the adult version, meconium is sterile and
odorless, though still pretty icky, and the sight of it in the newborn nursery starkly
reminds a new parent--not infrequently dad, since mom at this point is often out of
it--that his life has entered a dramatic new phase. (Nurses invariably offer to clean
things up. Let 'em.) I know what you're thinking: there's nothing much to nosh on in
there, so where's this stuff coming from? Various endogenous and swallowed sources: mucus,
bile, intestinal epithelial cells, lanugo (fine body hairs that are normally shed before
birth), and vernix caseosa (a lubricating sebaceous secretion of the skin).

Fetuses usually don't pass meconium until after birth, but doing so in the womb isn't
rare. Around 12 percent of fetuses have meconium-stained amniotic fluid (MSAF), colored
yellow or green by bile pigments in the meconium--an indication that junior couldn't wait.
The more prolonged the pregnancy, the greater the risk. In postterm births (those
occurring after 42 weeks), the rate of meconium staining is about a quarter to a half. Why
is this a concern? Fetuses take amniotic fluid into their lungs, and in a minority of MSAF
cases, passed meconium enters the airway before birth and afterward leads to respiratory
symptoms collectively called meconium aspiration syndrome (MAS). MAS can be fatal,
although the rate of deaths is falling in developed countries--in part due to better
treatments, but mostly because labor is now more likely to be induced if pregnancy drags
on.