Human chorionic gonadotropin and pregnancy: a primer

In this article, we will brief you on everything you need to know about human chorionic gonadotropin and pregnancy, from the first days of conception to the last days of the third trimester.

As you may know, wanting to get pregnant and actually conceiving are two totally different things. Even for women that have a healthy reproductive system, successfully fertilizing an egg for the first time is easier said than done.

During one’s efforts, it is important to keep an eye out for anything that might suggest the start of a successful pregnancy, as it is vital for any mother-to-be to make lifestyle shifts once they realize that they are about to have their first child.

One of the leading indicators of a successful conception is the presence of elevated levels of human chorionic gonadotropin, or hCG for short. As a result, the association between human chorionic gonadotropin and pregnancy is a very strong one (1). While this hormone is produced in limited amounts during each reproductive cycle, its production goes into overdrive the second that an egg is fertilized.

It is for this reason that home pregnancy tests look for the presence of hCG in a female’s urine. If it is present in large enough amounts, it turns the color of the strip blue, which indicates the presence of a possible pregnancy.

Human chorionic gonadotropin and pregnancy: why is it important, and how does it work?

In short, hCG stands for human chorionic gonadotropin, which is a hormone that is released by the placenta in ever-increasing amounts from the moment of conception until birth.

It starts getting released into the bloodstream not long after the egg attaches to the wall of the uterus, which occurs roughly nine days after it is fertilized in the fallopian tubes by a father’s sperm.

When it comes to human chorionic gonadotropin and pregnancy, the most important time for this hormone is at the very start of the process, as it is its increasing presence that compels the corpus luteum to continue releasing progesterone (2).

This hormone keeps the basal body temperature high and the endometrium intact, preventing the usual machinations of the latter half of the reproductive cycle from occurring (i.e. no period).

This keeps the pregnancy intact, thereby giving the newly implanted embryo the ideal environment to grow into a fully functional fetus.

After 10 to 16 weeks, the placenta will have developed enough to begin producing progesterone on its own, negating the need for the continued release of massive amounts of hCG. At this point, its levels will peak and then begin to slowly subside (3).

Trying for a baby: what to look for from hCG levels

When you are actively attempting to get pregnant, don’t get down if you getting negative results from your home pregnancy tests. hCG levels don’t begin to really spike until about two weeks after conception (4).

It takes time for the corpus luteum to increase in size and strength to the point where it is putting out enough human chorionic gonadotropin to get the lining of the uterus to remain intact, thereby giving the fledgling embryo the secure environment that it needs to grow into a fully grown fetus.

For the first two weeks, levels don’t surpass anything that could be considered normal during the course of a typical menstrual period. Afterward, elevated hCG levels that surpass 25 mIU/ml are almost certainly indicative of an early pregnancy (5).

However, there are a few rare conditions that could be responsible for a false positive. Most of these are not particularly pleasant to talk about, as several types of cancer can cause high hCG levels, as can the miscarriage of a very early pregnancy (6).

Certain types of antibodies can also interfere with readings, so if you have consistent positive home pregnancy test results but nothing to show for it, see your doctor as soon as possible (7).

Human chorionic gonadotropin and pregnancy: what do varying hCG levels mean?

Before we begin talking about what hCG levels mean during the progression of a pregnancy, it’s important to emphasize that the exact amount of this hormone can vary greatly from one woman to another.

We don’t want you to be looking at the number range below and stressing out because your reading is on the low end.

For what it’s worth, there have been many pregnancies with low overall hCG readings that have ended up resulting in the delivery of a perfectly healthy baby, so its important to not get obsessed over the relationship between human chorionic gonadotropin and pregnancy.

Wait until you are five to six weeks out from conception to get an ultrasound, as the images that it will produce will give your doctor a much better information on the health of your unborn child than solely relying on fluctuating amounts of hCG to draw conclusions.

Having said that, there’s a great deal that can be gleaned from the amount of this hormone in your urine and blood stream.

The first fact of which you should be aware: hCG will double in amount every 48 to 72 hours in the opening months, which makes it abundantly clear how much important human chorionic gonadotropin and pregnancy are to each other (8).

Later on in the term, the amount of time to double will expand to 96 hours. Further increases will persist until the placenta is able to produce progesterone on its own, at which time the corpus leutum will cease hCG production. Any major deviations from this should be grounds for a medical check-up.

Another major milestone will be when your hCG level approaches 2,000 mIU/ml. At this point, a gestational sac should have taken root in your uterus. When you reach this level, an ultrasound should be booked to assess the state of your pregnancy.

hCG levels should not be used to determine the age of a pregnancy, as the variance in levels of this hormone from one woman to another makes it very difficult for this marker to be taken seriously as an ironclad indicator of fetal development.

Indeed, levels of this hormone can vary greatly from one day to another within the same patient. As such, when getting checked for potential irregularities during a pregnancy, your physician will take multiple readings several days apart to smooth out the bumps between anomalous spikes and falls in hCG levels.  

Pregnant females can have levels of hCG as low as 18mIU/ml as late as five weeks into their term, or as high as 7,300 mIU/ml over the same time span (9). While it is prudent to track the amount of this hormone in your bloodstream, trained medical professionals should be the ones to make a diagnosis.

Focus on eating an optimal diet, getting moderate amounts of exercise, and managing any stress you might be feeling during your pregnancy, as all of these are factors within your direct control.

However, one thing you should watch for are rapid changes in your level of hCG. If they go up or down rapidly from the last reading that you took, be sure to get checked out by a specialist as soon as possible.

While we must again emphasize that hCG readings can vary widely for any number of reasons (many of which are normal), there are a small number of concerning conditions that are responsible for abnormally high or low readings.

When you record an hCG level that falls well outside expectations, get another reading within 48 to 72 hours to calibrate the initial result.

If you are confirmed to have a low level of hCG in your system, there is a chance that it might indicate that you have a blighted ovum, which is a fertilized egg that implants itself on the uterus, but fails to develop into an embryo (10).

When a drop in hCG occurs later in the first trimester, it may also indicate a miscarriage, though you should let a specialist come to that conclusion before putting yourself through the emotional stress of assuming this every time your hCG level drops (11).

If a miscarriage has in fact occurred, you can expect your hCG levels to return to non-pregnant levels within four to six weeks. However, continue to be tested for the presence of this hormone throughout the duration of this period, as it will ensure that no anomalous growths have taken root in the aftermath of this event.

You could also have an ectopic pregnancy, which is when fertilized egg implants itself on a body structure outside the uterus. 1 out of 50 times, an embryo starts growing in the fallopian tubes, on an ovary, on the cervix, or even in the abdomen (12).

Sadly, there’s little chance of the fetus surviving in these situations, as they must be moved in order to save the life of the mother.

In the majority of cases though, a low hCG reading is the result of a poorly dated pregnancy. A few tests by a reproductive specialist will be able to establish the true age of your unborn child, allowing you to reset your expectations surrounding the rise and fall of hCG in your body.

What about an abnormally high level of hCG? As with low hCG levels, you should wait 48 to 72 hours after your initial anomalous result before taking another reading.

If you do have high levels of hCG, it points to something that is fairly harmless (though your pocketbook may disagree, as you will find out in a moment). However, this reading may be a symptom of a molar pregnancy.

A molar pregnancy is when a fertilized egg fails to develop into a fetus, and instead turns into an abnormal growth of tissue resembling a bunch of grapes (13).

Occasionally, it is the placenta that spurs a partial molar growth, which can result in any fetus with severe birth defects, should it manage to even survive.

In all cases, the growth or any embryo that exists along with it will need to be removed in order to protect the health of the mother.

Having said that, most cases of high hCG levels mean one of two things: either your reproductive specialist miscalculated the age of your pregnancy, or you’re about to have twins (or triplets, or…) (14).

In the first case, tests will be done to re-establish the age of your unborn child, and in the latter case, you will quickly need to find room for more than one child in your house, as well as in your financial plans.

Elevated hCG levels don’t always mean you’re pregnant…

While sky high hCG levels are cause for celebration in the vast majority of cases, there are some instances where it can be symptomatic of something far more sinister.

While a developing fetus will put out ever increasing amounts of this hormone, the same will occur when benign and malignant growths have taken up residence in the uterus. Many of these are caused by flawed eggs being fertilized, resulting in a mass of useless tissue.

As mentioned earlier, this is known as a molar pregnancy. This event can occur after a miscarriage as well, which explains why many reproductive specialists will continue testing you for hCG even after you have suffered through the emotionally crushing experience of losing your baby.

Other cancers of the uterus such as a choriocarcinoma also trigger an increase in hCG, so if you have been suffering excessive bleeding from the vagina, you will want to get tested for elevated levels of this hormone to be safe (15).

An interesting side note: men that are suspected to have testicular cancer are also tested for elevated amounts of hCG in their system, as tumors produced by this disease cause the production of this hormone as well (16).

Don’t freak out: that time when your hCG levels began to fall (and it was totally normal)

While the level of hCG in the bloodstream exponentially increases from the moment of conception, there is a point where the level of this hormone peaks and begins to tail off.

The escalating level of hCG helps to maintain the integrity of the pregnancy while the placenta is in the process of growing.

This is to help keep the amount of progesterone between the ovary and the corpus luteum in balance until the placenta is in the position to produce progesterone on its own.

Between 10 to 12 weeks into the pregnancy, the placenta will be in the position to be able to produce its own progesterone, causing a fall in hCG levels, as it has finished serving its purpose. After everything that we have talked about with regards to dropping hCG levels, it’s important not to freak out when this occurs.

Pregnancies that have been improperly aged have triggered many of panic attacks in many mothers-to-be, as the hCG level drops off as it should, which is when the placenta in the position to make its own progesterone.

However, the fetus may be perceived to be younger in the mind of the mother, making a drop in this hormone much scarier, as it implies a potential miscarriage (17).

For this reason, it is important not to jump to conclusions when a sudden drop in hCG is detected, as it can be hard to gauge the age of a fetus at the best of times.

Don’t freak out, part II: screening tests for potential birth defects

The relationship between human chorionic gonadotropin and pregnancy goes beyond its mere detection (and sadly, of failed fetuses and potential cancers as well), as its levels can also be evaluated to determine the health of your baby/twins/triplets/etc.

15 to 20 weeks after conception, reproductive health specialists will conduct a series of tests to determine the probability that the fetus you are carrying might be harbouring birth defects.

Over the course of three to four samples, your maternal serum will be examined for abnormal levels of hCG, as well as substances like alpha-fetoprotein and unconjugated estriol.

Based on these results, as well as other factors such as the age of the mother, your doctor will be able to tell you whether you might have to deal with certain health issues upon the delivery of your child (18).

How to give urine and blood samples

Human chorionic gonadotropin and pregnancy have such an important correlation with many events during this time. As such, it is important to know how to give an effective sample will make the results that they produce reliable.

Blood tests, though phobia-inducing for some, does not require any pre-sample preparation. If you opt to give urine samples, it is best to collect it first thing in the morning, as this sample will generally have the greatest concentration of hCG compared to other times during the day (19).

If you forget to collect it during your first trip to the toilet, waiting four hours after the last urination event will also yield statistically significant amounts of hCG.

Blood tests yield more reliable results than urine, especially early on in a pregnancy. While this method may not be preferable or even possible for reasons mentioned previously, most blood draws are painless or are signified by only a quick pinch, and at worst, by some bruising at the injection site.

One group that should opt for the urine test over having their blood drawn are those that are on blood thinning medications, or ones that suffer from clotting problems.

For everyone else, simply looking away from the injection site and engaging the nurse in small talk will be enough to distract you from the needle that is about to go into your arm.

 

References:

(1) http://www.tandfonline.com/doi/abs/10.1185/03007990902743935

(2) http://www.ncbi.nlm.nih.gov/pubmed/18694877

(3) http://www.webmd.com/baby/human-chorionic-gonadotropin-hcg

(4) http://americanpregnancy.org/while-pregnant/hcg-levels/

(5) http://americanpregnancy.org/while-pregnant/hcg-levels/

(6) http://www.ncbi.nlm.nih.gov/pubmed/15234236

(7)http://www.fda.gov/MedicalDevices

(8) http://americanpregnancy.org/while-pregnant/hcg-levels/

(9) http://americanpregnancy.org/while-pregnant/hcg-levels/

(10) http://www.webmd.com/baby/guide/blighted-ovum

(11) http://www.livestrong.com/article/407996-hcg-levels-after-a-miscarriage/

(12) http://www.medicinenet.com/ectopic_pregnancy/article.htm

(13) http://www.mayoclinic.org/diseases-conditions/molar-pregnancy/basics/definition/con-20034413

(14) http://www.livestrong.com/article/321696-hcg-levels-when-pregnant-with-twins/

(15) https://medlineplus.gov/ency/article/001496.htm

(16) http://www.cancer.org/cancer/testicularcancer/detailedguide/testicular-cancer-diagnosis

(17) http://americanpregnancy.org/while-pregnant/hcg-levels/

(18) http://americanpregnancy.org/birth-defects/

(19) http://www.healthline.com/health/hcg-in-urine#Preparation4

 

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