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Causes of Early Miscarriages at 6 to 8 Weeks

Hello I'm Norbert Gleicher, MD and I'm the medical director and chief scientist here at

the Center for Human Reproduction. I would like to address today a problem

that we very frequently are asked about and that is the early miscarriage.

Miscarriages or pregnancy loss can occur at any stage of pregnancy. When it

happens very very early before we can visualize a pregnancy on ultrasound we

call it a chemical pregnancy and those are miscarriages but they're so early

that we do not consider them in pregnancy statistics. So when we or the

fertility centers report their "pregnancy rates" in various patient populations

that usually should exclude those chemical pregnancies but they are still

pregnancies and they have clinical meaning because if you detect pregnancy

hormone HCG in the blood of a female and she didn't receive it as a medication,

then that means that an embryo must have implanted because only the embryo

produces this HCG and if this HCG has been found in the blood of the mother the

only way that the fetal product shows up in the blood of the mother is if

implantation has taken place. So for clinical purposes this is a very

important point because it obviously is important to know whether a woman even

can achieve an implant and there are studies in the literature

from the early days of IVF where it was shown that women who go through, for

example, a first IVF cycle and have a chemical pregnancy, once they go into a

second IVF cycle have a better pregnancy chances than 100 women who in the first

IVF cycle just had a negative pregnancy test.

So there's importance to the chemical pregnancy diagnosis even though we don't

count it as a real pregnancy. We are talking about the clinical pregnancy

once we can see an ultrasound and that depends on the equipment and the skills

of the operator of the ultrasound but in principle with currently available good

ultrasound equipment, we should see pregnancy shortly after five weeks

gestational age which in terms of IVF cycle outcomes really means roughly

three weeks post-transfer because when we date pregnancies, we still are

adhering to actually completely outdated habits of going back to the supposedly

first day of last menstrual period which obviously is about two weeks

before an embryo transfer takes place in IVF. So in the early pregnancy an early

clinical pregnancy must be seen on ultrasound and it is usually seen only

as a round gestational sac and then, depending on the age of the pregnancy,

every week or so we see more and more. So at five weeks we will see a small

gestational sac, by six weeks we should already see a little fetal pole with the

heart beating. By seven weeks we should already see a good fetal representation

and obviously with continues normal fetal heartbeat over 140 beats per

minute. Yes, the fetal heart beats much quicker than our heart does and normal

fetal heart beats at over 140 beats per minute. So that's as a way of background.

Now at all of these stages and even into the second trimester the pregnancy can

miscarry and the causes can vary. It is in general assumed that the most

frequent cause for early miscarriages are chromosomal abnormalities and that

is probably still true and correct except that as we now are

learning more about the genetics of early embryos we have to kind of

reinterpret what has been published over past decades and the reason is very

simple - all of our information about the causes of early miscarriages stem from

pathological examinations off those miscarriages, meaning a woman has a

miscarriage there are what's called products of conception available. They're

sent to pathology they're looked at under the microscope and more

importantly, they're spread out, meaning we are taking a bunch of cells and

testing their chromosomal makeup. Now, historically that used to be done by

culturing those cells for a few days and then doing what's called a spread.

And that was a very reliable and successful method in determining whether

those cells or those bunch of cells, meaning that biopsy that we used from

the products of conception were chromosomally normal or not. Turns out

that the data we have been generating for many many decades and in that way

are really not completely correct and the reasons are technical. Our pathology

colleagues and our genetics colleagues always told us when we take tissue and

send it to pathology to take it from the placenta from the placental part rather

than the fetal part and that's what we have been doing for decades. Except that

now we know that there is a difference at times in the chromosomal makeup of

the placenta and the fetus. The placenta is much more frequently showing

chromosomal abnormality than the fetus. And therefore now that we know that we

also have to understand that all the numbers we accumulated over the decades

that told us that maybe up to 80% of early miscarriages are chromosomal in

nature, they are probably more likely highly exaggerated. And that is important

news because more recent data using more modern genetic diagnostic tools

suggests that the real rate is probably closer to only 50%, maybe even lower than

that, and that has obvious meaning because that means that a much larger

part of early miscarriages that we used to believe in and that even textbooks still

today are telling us may have other causes than chromosomal abnormalities.

And that is obviously a very significant clinical importance because in order to

look for something, we have to know that there is a suspicion for something. So we

used to be kind of lazy in the past about miscarriages and when the

miscarriage happened early on we used to think "oh it's chromosomal." No longer it is

at best 50/50 and maybe even less so if you have a miscarriage discuss with your

obstetrician-gynecologist or fertility specialist.

The possibility of testing your pregnancy because it is clinically very

important to know whether when you lose a pregnancy if it was a chromosomally

normal pregnancy or not. If it was a truly chromosomally abnormal pregnancy,

then it's usually a random even, there's no big meaning to it, but if it

turns out that your early pregnancy loss is chromosomally normal and a normal

female or a normal male then this really means that there is a different reason

for the miscarriage and it means that we really need to find out what that reason

is if we want to prevent it from happening again. Thanks very much for

listening.