Elevated AFP in maternal serum and amniotic fluid
Pologirl
Hi all!
Over on misc.kids.pregnancy someone is asking for information about
elevated AFP in both maternal serum and amniotic fluid. Those of you
with an interest in this, please take a look!
My gut feeling is this may be a false positive, meaning the baby is
normal, just one of those babies who has a very high AFP for no
apparent reason.
Pologirl
(There does not seem to be any way for me to crosspost this to
misc.kids.pregnancy...?)
Una
but not TFD. So I'm posting it again, this time just to TFD.)
Oh boy. This gets really complicated. The MS AFP is 5MoM and the
AF AFP is 16MoM, but on ultrasounds the baby appears to be healthy.
The simple answer is that MS AFP and AF AFP are *screening* tests.
Some authorities even suggest dropping them, if ultrasound exams
are routinely available, and rely on ultrasound exams instead. By
this reasoning, there is no evidence of anything to worry about.
The more detailed answer has several parts.
1. Worldwide, numerous published studies establish reference
ranges for AFP in healthy babies. Together, these studies involve
many thousands of babies of many different ethnicities. Most of
these studies use a common method to calculate a 97.5% confidence
interval ("normal range"), which gives an upper bound at about
5.6MoM. However, in most of these studies the "outlier" babies'
AFP values are *far* above the upper bound. These babies are
healthy too; they just don't fit the pattern established by other
babies.
2. At birth, healthy male babies compared to healthy female babies
have a far wider distribution of AFP in their urine. SIgnificant
to this case is that here again a small fraction of healthy male
babies, "outliers", have AFP values in excess of 10 MoM. (This is
>from a bar chart: the actual value could be in excess of 20 MoM.)
3. The relationship between fetal serum and fetal urine (ie
amniotic fluid) AFP values is approximated by a simple multiplier
(fetal serum = 400 * fetal urine). This means that in a healthy
fetus AF AFP is a very good estimator of fetal serum AFP.
So, at this point the AF AFP, although high, is not proof that
something is wrong. Such a high value is possible in a healthy
fetus, particularly in a healthy male fetus. Considering that
most of the things that could be wrong are *rare*, the odds are
good that this male fetus is a healthy "outlier".
What's left?
4. Mizejewski (ref below) reviewed the literature and reports
elevated AF AFP to have known links with 12 conditions. 8 of
those 12 conditions would be very apparent on an ultrasound fetal
anomaly exam (and some are AFP leaks into AF, not elevated fetal
AFP, so they don't contribute to elevated MS AFP). In this case,
after 3 US exams, the US-apparent conditions can be ruled out, at
least tentatively. That leaves just these:
* Yolk sac tumor aka endodermal sinus tumor, pure or mixed, somewhere
in the fetus (head to pelvis) where US does not differentiate it from
surrounding tissue, and too small to reveal itself on US by displacing
other organs. (Mizejewski's list has "teratoma" but as a rule teratoma
secretes AFP only when it is mixed, with elements of yolk sac tumor.)
* Congenital skin defect (unspecified; would have to read Mizejewski's
refs).
* Cystic hygroma (on the list b/c reported but I doubt it is valid:
hygroma normally does not secrete AFP).
* Congenital nephrotic syndrome.
* A condition not on the list of 12, ie not already known to elevate
fetal/AF AFP, and not apparent on US exams.
I think the bottom line message is that at this time there is no sure
sign of anything wrong and odds are the baby is healthy. But, the
above short list provides some specific conditions to look out for /
rule out, in addition to continuing to monitor the pregnancy closely.
To the OP: congratulations on expecting a baby! Please check in and
let us know how you get on: your baby boy, your wife, and yourself.
Best wishes,
Una (another mom to a survivor of a fetal germ cell tumor)
Mizejewski GJ.
Levels of alpha-fetoprotein during pregnancy and early infancy in
normal and disease states.
Obstet Gynecol Surv. 2003 Dec;58(12):804-26. Review.
PMID: 14668662
Pologirl
This discussion is continuing in misc.kids.pregnancy (thanks, Una).
Pologirl