Issues that can prevent pregnancy

While there are many things that have to function for pregnancy to happen, there are also a few things that can go wrong. It’s natural that pregnancy might not occur every month even when you time intercourse correctly, but some things can make it harder than it should be.

Remember - things are seldom black and white when it comes to fertility. Most of these issues don’t make it impossible to conceive, but can make it harder. That’s where fertility treatment and lifestyle changes come in - they can help optimize chances if something is not working as it should. But before rushing into finding a solution, it is key to identify the issue first.

Ovulation issues

To get pregnant, the presence of an egg is vital - without it, the rest of the reproductive process can’t happen. Ovulation is therefore crucial - without it, no egg is released and there would not be an egg to meet the sperm in the fallopian tube.

Although being vital, ovulation is a sensitive process that depends on the right hormonal balance at each stage of the menstrual cycle. Ovulation issues are in fact the most common reason for female fertility issues. 

That said, it’s important to highlight that we are referring to recurring ovulation issues because the occasional missed ovulation is not something to worry about. It is when ovulation is irregular that it becomes a problem. Irregular ovulation makes it very difficult to track and to time sex correctly, not to mention that it reduces the chances of fertilization. Anovulation, or not ovulating at all, makes it impossible to become pregnant. 

Why ovulation might not occur

There are different reasons ovulation may not happen, and most of them are connected to hormonal imbalances: 

  • Polycystic ovarian syndrome (PCOS)
  • If the hypothalamus is not secreting enough Gonadotropin-releasing hormone (GnRH), the pituitary gland will not receive signals to produce the luteinizing hormone (LH) and the follicle-stimulating hormone (FSH) needed to stimulate follicle growth and eventually, ovulation.
  • Excessive prolactin
  • Gland issues
  • Certain medicines
  • Being over- and underweight
  • Diabetes
  • Early menopause

Detecting ovulation issues

It is possible to identify ovulation issues yourself by tracking your cycle and ovulation. The most obvious sign to look out for is irregular periods, or amenorrhea, which is to not have periods at all. A regular cycle is a good sign that ovulation is working as it should - it’s not a 100% guarantee that ovulation issues are not present, but a regular cycle without ovulation is uncommon.

If you have an irregular cycle, a blood test measuring your hormone levels should be taken to try to identify the cause. A hormone blood test can also be taken proactively to exclude issues such as PCOS, low estrogen, or high prolactin, for example.

A depleting egg reserve (low AMH) or early menopause

What is an egg reserve?

Women are born with all the eggs they’ll ever have, so the egg reserve - or the number of available eggs – naturally decreases with time. Menopause is when you have your last ovulation and period. When you reach that point, you basically have no eggs left. On average, menopause occurs around the age of 51. But for up to 10 years before that, you may experience symptoms that happen due to a declining egg reserve and related changes in hormone levels, otherwise known as the climacteric period. 

There is often a lot of focus on the number of eggs and the Anti-Müllerian Hormone (AMH) value. The AMH value is a hormone value that indicates how large your egg reserve is, but it is really only one part of the equation. Studies show that a woman with a lower egg reserve, with no other issues, has the same chance of conceiving during the first year trying as someone with a higher egg reserve. But with maturing age and a declining egg reserve, the hormonal balance also shifts. On top of having fewer eggs, maturing women generally ovulate less often, and the share of healthy eggs declines – read more about egg quality below.

A significantly low egg reserve evidently decreases the chances of getting pregnant, and it can also make an IVF treatment more complicated as it may be hard to stimulate the growth of many follicles. 

Early menopause / POI

For about one in a hundred women, the egg reserve declines at a younger age than average. In “early menopause” or primary ovarian insufficiency (POI), some women have no symptoms other than being unable to become pregnant, while others have menopausal symptoms such as a changing menstrual cycle, hot flashes, or night sweats.

Depending on how far the process has gone, the eggs may not have been depleted completely. Becoming pregnant may still be possible, but is more difficult. IVF is often needed even if stimulating follicle growth with hormones can be a challenge. 

Detecting a depleting egg reserve or early menopause

AMH, a hormone that indicates the size of the egg reserve, can be measured via a blood test. Normally FSH and estrogen levels are also considered since these hormone levels are also affected when egg reserve declines. Along with your age, menstrual cycle, and symptoms - it’s important to get a full picture to conclude whether the change is natural for your age and how far the process has gone before deciding on the next step. 

Considering that a simple blood test can exclude a major risk factor, more proactive screening of women’s AMH-value would be preferred. But just remember - a high egg reserve is no guarantee for high fertility. Other factors play a role as well.

Poor egg quality

Unfortunately, not all eggs have normal chromosomes and can develop into healthy embryos that result in successful pregnancies. 

During egg maturation, the crucial process of meiosis takes place. An egg needs to shed half its DNA blueprint, going from 46 to 23 chromosomes, making room to combine with the sperm’s DNA. Healthy eggs, therefore, have 23 chromosomes, the same as healthy sperm. A successful embryo, or fertilized egg, is created when there are 46 chromosomes which are the same as all other cells in the human body. 

If an egg is not of high quality with healthy chromosomes, three things could happen: either it does not fertilize, the embryo does not implant or an early miscarriage occurs.

One of the reasons that pregnancy isn’t always successful, even with correctly timed sex, is that not all the eggs in the egg reserve that a woman has are healthy. When doctors say that a miscarriage is generally “bad luck” that’s what they mean - you were unlucky enough to become pregnant with a low-quality egg, or sperm. Egg quality declines with age, which is one of the main reasons that the chances of pregnancy decline each cycle, and the risk of miscarriage increases.

Detecting egg quality issues

Unfortunately, there’s no test you can take to measure egg quality proactively. Usually, it’s identified while undergoing IVF and embryologists watch the embryos develop in a lab.

If you are undergoing IVF, it is also possible to conduct a pre-implantation genetic diagnosis (PGT-A). This test screens embryos for chromosomal issues before they are returned to your uterus.

At the root of it, age is the best predictor of egg quality. The egg cells go through the same process as all other cells in the body that makes us wrinkle when our skin cells age. The number of healthy eggs will also naturally decrease with age.

In your 20s, the chances of getting pregnant within a month of having sex during the fertility window are about 25-30%. In your 40s this drops to 5%, which is largely due to deteriorating egg quality. The risk of miscarriages also increases as you get older. 

In general, you can see that when at around 25 years old, about 75% of your eggs have a healthy set of chromosomes. However, that proportion is about 50% when you reach 35 years and is only 10-15% when you reach 40 years of age.

Of course - these are average numbers and all women are different. There are lifestyle choices that can speed up the decline in quality, but there’s nothing you can do to completely stop the aging of eggs.

Sperm issues

Like the egg, the presence of sperm is also non-negotiable in the process of getting pregnant, and must not be forgotten when considering issues related to fertility. There can be many underlying factors, but issues can be broken down into 3 types: 

  • Insufficient sperm production - ie: not enough sperm.
  • Reduced sperm quality and motility - ie: not enough normal or motile sperm.

Insufficient sperm production

In theory, only one sperm is needed to fertilize an egg. In reality, though, the journey of one sperm to meet an egg is long and arduous. Did you know that only 1 out of 14 million sperm actually make it to the fallopian tubes to meet the egg? The distance from the cervix to the fallopian tubes may only be around 18cm long but for the sperm that is about the distance of a person swimming from California to Hawaii… and back. Basically, only very few of the sperm ejaculated reach the egg. 

In general, there are three reasons someone wouldn’t make enough sperm:

  • The testicles aren’t being prompted to make sperm.
  • The testicles are being prompted, but won’t cooperate.
  • The testicles are cooperating, but some blockage keeps the sperm from being ejaculated.

Pregnancy is still possible if fewer sperm are released, under the amount of tens of millions. It is unlikely to happen naturally, though. However, if there is absolutely no sperm being released, conception can only happen with some help.

Reduced sperm quality and motility

If sperm aren’t capable of swimming forward, they will never make it where they need to go to find the egg. Likewise, if some sperm survive and make it where they need to go, they might still be unable to fertilize the egg. If sperm aren’t capable of both swimming and fertilizing, the natural process cannot proceed.

Detecting sperm issues

Sperm quality is measured by assessing sperm samples and not usually conducted unless there are issues when trying to conceive. It can be done proactively though, which is especially useful if the man has been through:

  • surgery in the scrotum, e.g. due to scrotal hernia.
  • surgery for a non-migrating testicle.
  • an infection of the scrotum or prostate.
  • major trauma to the scrotum that required a doctor's visit or even surgery, e.g. a large blood clot.
  • testicular torsion, which affects the scrotum.
  • an infection of mumps as a child.
  • exposure to medication that is known to affect fertility.
  • exposure cytotoxic drugs or radiation.
  • problems with erection or ejaculation

Damaged fallopian tubes

Getting pregnant naturally will also not happen if the fallopian tubes are blocked or damaged in any way. For example, if a fallopian tube is blocked, the egg and sperm will not be able to meet there and fertilization cannot occur. And if there is scar tissue, it will not be able to suction eggs out of the ovary.

The tubal function could be damaged due to many reasons; endometriosis, previous infections like sexually transmitted infections, or an ectopic pregnancy when pregnancy takes place in a tube instead of in the uterus. Smoking has also been shown to damage tubes. 

Women are born with two fallopian tubes and if only one is lost or damaged it could take a little longer to become pregnant, but it is usually possible. If both are damaged, IVF is usually recommended. Fertilization then takes place outside of the body and the embryo is placed straight into the uterus so a tube isn't really needed. 

Detecting issues with the fallopian tubes

The following techniques can be used to examine fallopian tubes:

  • Hysterosalpingography
  • Sonohysterography
  • Laparoscope

Issues with the uterus

There are several issues that could cause a uterus to be unable or less likely to support a successful pregnancy. There may be issues with the anatomy of the uterus itself or hormonal functions, or issues with the lining of the uterus. 


These are some of the different ways that the structure and internal workings of the uterus itself can affect fertility. 

Abnormal shape

Some women are born with an irregularly shaped uterus - for example, they can be heart-shaped (bicornuate) or divided (septate). Each irregular shape comes with different issues but it is also possible for women with abnormally shaped uteruses to carry a baby to term without a hitch.

Fibroids, polyps, myoma

Fibroids, polyps, or myoma in the uterus can cause heavy bleedings and cramps. Fibroids that distort the shape of the uterine cavity are an issue because they prevent the embryo from implanting successfully on the uterine wall. There is some evidence that if the fibroid changes the shape of the uterine cavity, sometimes described as being “submucosal or intramural with a submucosal component”, removing it through hysteroscopic myomectomy can improve the chances of conception.

But if a fibroid doesn’t appear to change the shape of the uterine cavity, it might not impact fertility as much. From a fertility standpoint, it is hard to tell if treating a uterine fibroid improves the chances of getting pregnant. The issue likely comes down to where the fibroid resides.


Endometriosis is a condition where the tissue that lines the uterus develops outside of the uterus. It often causes heavy bleeding and cramps. Endometriosis does not always cause issues to conceive, but women with endometriosis are over-represented among fertility patients.


Some research also suggests that infections of the uterine cavity, sometimes referred to as endometritis, or chronic inflammation may be associated with embryos implanting on the uterus or miscarriage. This can usually be treated with antibiotics.

Issues with the lining or hormonal function 

Scar tissue can make implantation harder for an embryo. This can be a result of previous procedures involving the uterus such as dilation and curettage (D&C), a procedure to remove tissue from inside your uterus, or past C-sections.

It also becomes harder if hormonal imbalances cause the lining not to develop properly. It becomes less likely that an embryo will implant and get the nutrition it needs from the endometrial lining that is not thick enough.

Hormonal imbalances

Hormones are crucial to the process of reproduction and they set off a cascade of events that need to happen in a specific order and at a specific time. This is why even the smallest of problems can throw everything off.

Women need to have the right amounts of hormones like FSH, LH, estrogen, and progesterone, not only for ovulation, but also to grow the uterine lining to ensure successful implantation.

Men need the right concentrations of testosterone, FSH, and LH as well, to produce sperm.

Hormones and the glands that produce them are affected by everything we do, which is why things like chronic stress, diet, and exercise must always be considered. Unfortunately, it’s not simple and different bodies have different requirements and react differently to lifestyle choices. It’s also always important to understand one’s issue before deciding on a plan for how to solve it. For a woman, using the menstrual cycle as a diagnostic tool is a great first step to keep track of hormonal health. An irregular cycle is always a sign that something is not working as it should. Of course, a hormone test can also give a clearer picture when in doubt.


Evangelia Elenis, MD, PhD.

This text is fact checked by Evangelia Elenis, MD, PhD. Dr. Elenis is a chief physician in Obstetrics and Gynecology, and a subspecialist in Reproductive Medicine. She is a PhD and affiliated researcher at Uppsala University with postdoctoral studies at Harvard Medical School.

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