Low Progesterone Levels in Early Pregnancy: A Symptom or Cause of Miscarriage?

What came first – the miscarriage or low progesterone during pregnancy? This is one of the most often asked questions when it comes to early pregnancy loss. Progesterone is THE major pregnancy hormone – it is literally PRO-gestation. That’s why it is an easy target and is so often blamed for when pregnancies aren’t successful and end in miscarriage. In most cases of pregnancy loss, low progesterone levels are a SYMPTOM rather than a CAUSE of abnormal pregnancy. In order to understand this, it is crucial to understand the role of progesterone in the menstrual cycle and establishment of early pregnancy.

What is Progesterone and What Does it Do in Pregnancy?

Progesterone is an essential reproductive hormone that plays a critical role in establishing and maintaining a healthy pregnancy. It is produced by the corpus luteum, which is the remaining follicle in the ovary after an egg has been released through ovulation.

After ovulation occurs, the corpus luteum starts secreting progesterone to prepare the uterus for possible implantation of a fertilized egg. Progesterone supports the uterine lining, called the endometrium, and prevents contractions and menstruation so that the endometrium stays thick and vascularized. This provides the optimal environment for an embryo to implant and grow.

If fertilization occurs and an embryo successfully implants into the uterine lining, the embryo will start producing the hormone Human Chorionic Gonadotropin (hCG). hCG acts as a signal to the ovaries and corpus luteum to continue producing progesterone to support the early pregnancy. Progesterone helps stabilize the endometrium and maintains the pregnancy until the placenta fully develops around 10 weeks gestation. At this point, the placenta takes over producing progesterone and other hormones needed to sustain the pregnancy through the second and third trimesters.

Progesterone is absolutely essential for creating an environment conducive for embryo implantation and early pregnancy maintenance. It prevents shedding of the uterine lining and enables an embryo to safely implant and establish nurturing connections to the mother’s blood supply. Progesterone also inhibits uterine contractions that could expel an embryo in early pregnancy. Through these mechanisms, optimal progesterone levels foster a healthy pregnancy.

Why Do Progesterone Levels Drop in Nonviable Pregnancies?

In the majority of early pregnancy losses and miscarriages, rather than low progesterone levels directly causing the loss of the pregnancy, it is actually the other way around. An unhealthy pregnancy that is nonviable and destined to miscarry will not produce adequate levels of hCG to appropriately signal the corpus luteum to keep producing Progesterone. This results in dropping Progesterone levels.

The sad truth is that most miscarriages occur due to genetic or chromosomal abnormalities in the embryo that prevent proper development. Other uterine and structural issues like fibroids, polyps, or a septum in the uterine cavity can also hinder implantation and lead to miscarriage. These underlying problems and dysfunction cannot be resolved or reversed by simply supplementing progesterone.

In fact, supplementing Progesterone in a nonviable pregnancy may actually prolong a doomed pregnancy rather than prevent an inevitable miscarriage. It could delay the completion of the miscarriage process, extending the emotional agony of waiting and wondering what is happening.

Progesterone supplements do not salvage genetically abnormal embryos or fix structural uterine abnormalities. Many women understandably feel compelled to “do something,” and Progesterone seems like an easy, non-invasive option. However, most of the time, low Progesterone is not the root cause behind early pregnancy loss. Attempting to increase Progesterone in these cases provides false hope and does not improve viability.

In some cases, short luteal phases and low Progesterone production may result from underlying medical conditions like hypothyroidism, excess intense exercise, poor diet and low body weight, or problems with hormone signaling from the pituitary gland in the brain. But generally, low progesterone does not directly cause miscarriage in an otherwise normal pregnancy. The focus should be on identifying and addressing any underlying medical causes contributing to recurrent miscarriages or hormone level abnormalities.

What Progesterone Levels Are Normal in Early Pregnancy?

Because Progesterone is released in a pulsatile fashion, there is no single established threshold that guarantees a healthy, viable pregnancy. Levels fluctuate both throughout the day and across the first trimester.

However, there are general guidelines physicians follow:

• A Progesterone level above 3 ng/mL in the week following ovulation indicates that ovulation did successfully occur.
• Studies have shown that healthy pregnancies can be supported with Progesterone levels between 2.5-18 ng/mL.
• Levels above 10 ng/mL in early pregnancy are considered encouraging, but not definitive.
• There is quite a lot of overlap between Progesterone levels in viable and nonviable pregnancies. A single Progesterone measurement does not consistently predict viability or miscarriage.

Evaluating trends in Progesterone levels across multiple points in time provides more clinically useful information than one random single value. For example, declining Progesterone levels over a week rather than a stable plateau may indicate an increased risk of impending miscarriage. I would never make a judgment about the viability of an early pregnancy based on a single progesterone level.

Each woman also has her own baseline hormone levels, so tracking an individual’s changes from her norm provides personalized data.

Should I Take Progesterone Supplements?

In pregnancies conceived through In Vitro Fertilization (IVF), Progesterone supplementation is universally required. This is because the ovulation induction process does not allow the follicle to transform into a fully functional corpus luteum that secretes hormones normally. Therefore, exogenous Progesterone must be provided.

However, in spontaneous natural conceptions, Progesterone supplementation is generally not recommended unless specific medical circumstances exist.

Taking Progesterone supplements when not clinically indicated could potentially have detrimental effects. Starting supplementation too early after ovulation could shift the window of implantation in the endometrium, making the timing less favorable for the embryo to implant properly. This could then negatively impact the chances of achieving a successful pregnancy.

There is some limited evidence that Progesterone supplementation may help prevent bleeding in women who have experienced recurrent pregnancy losses. However, the data is not robust enough to support blanket recommendations for Progesterone in recurrent loss.

In the majority of miscarriages not related to significant hormonal disorders, Progesterone supplements do not conclusively improve viability or prevent loss. The priority should be identifying any underlying disorders or abnormalities causing recurrent losses through thorough evaluation. Addressing potential structural, genetic, or hormonal issues will provide more benefit than progesterone alone.

Progesterone supplementation does not act as a magic bullet or band-aid to save nonviable pregnancies. While the desire to do everything possible to support a pregnancy is understandable, unnecessary supplementation will not rescue or prevent an inevitable early loss. It merely draws out the process.

It is also important not to view Progesterone levels in isolation. Pay attention to trends in hCG levels as well, as they provide additional data about pregnancy health and are closely tied to Progesterone activity.

Work closely with your Reproductive Endocrinologist to determine if Progesterone supplements may be appropriate in your specific clinical scenario. But understand that in most cases, supplementation will not impact the unfortunate outcome.

Key Takeaways

• In the majority of miscarriages, low Progesterone is a consequence of an unhealthy, nonviable pregnancy rather than the cause of pregnancy loss.
• Declining Progesterone levels frequently reflect lack of adequate hCG signaling, not an intrinsic progesterone production problem.
• Progesterone levels and trends provide useful data about pregnancy viability, but no single threshold can definitively predict success or failure.
• In natural conceptions, Progesterone supplements do not resolve genetic abnormalities in embryos or structural uterine issues leading to miscarriage.
• Blindly taking Progesterone supplements could negatively impact pregnancy chances and will not prevent inevitable losses.
• Underlying disorders affecting ovulation, hormone levels, and cycle regularity should be addressed to improve Progesterone function.
• Progesterone supplementation is ineffective at salvaging nonviable pregnancies and does not prevent inevitable early miscarriage.
• Do not regret not taking Progesterone or blame yourself for miscarriage. Pregnancy loss is not your fault and is often out of your control.
• Work with your doctor to interpret your Progesterone levels in context, alongside other hormone data, for personalized clinical guidance.
• Focus on identifying any reversible causes of recurrent losses through proper testing. Progesterone supplements alone are rarely the solution.

Low Progesterone Does NOT Cause Miscarriage

Understanding the relationship between Progesterone levels and pregnancy viability provides important insight into managing recurrent early losses. However, it is clear that low Progesterone is far more often a symptom rather than the cause of miscarriage. The bottom line is – if you had a miscarriage and have no known underlying hormonal imbalances or pituitary/thyroid problems, it was VERY unlikely caused by a Progesterone deficiency or resistance of your body to the effects of progesterone. If such problems exist, they would be extremely rare.

When it comes to low progesterone – it is the consequence of an unhealthy pregnancy, not the cause. As much as we wish to have control and the ability to use Progesterone like a band-aid of sorts, to salvage and rectify any early pregnancy abnormalities, we know that it seldom is the answer. The important takeaway is that you should not regret not taking Progesterone – and there was likely nothing that could have been done to modify the outcome.

Miscarriage is NOT your fault and NOT in your control.

The only thing we can do is observe and collect data points as early indicators of whether a pregnancy will be likely to persist – and Progesterone and HCG levels are the most useful predictors of pregnancy health and success.