Important: This is intended as general information only. It may not apply to your specific situation.  It is not a substitute for medical advice.  If you have a question or concern, please raise it with me at your next appointment or contact me sooner if it's urgent.


A miscarriage is defined as the loss of a pregnancy before 20 weeks gestation.  This means that the fetus stops developing and passes away before reaching 20 weeks gestation.  Most miscarriages happen before 10 weeks and most of these are between 6 and 8 weeks gestation.  Miscarriages are more common than you may think – at least one in five, and maybe as many as one in four, early pregnancies miscarry.  These days, with sensitive pregnancy tests and ultrasounds, we can diagnose miscarriages that, a generation ago, might have been put down to an irregular cycle. 

Having a miscarriage is a very sad, and often quite difficult, situation for a couple to be in.  Some women find that understanding more about the causes of miscarriages helps them deal it a little better.

Common First Trimester Miscarriages

Most miscarriages happen between 6 and 8 weeks gestation.  We know that most of these occur due to a major genetic abnormality in the fetus. 

The sperm and the egg (which are known as gametes) each contain half the genetic material necessary for a complete person.  They are made when a complete cell divides in a process known as meiosis –resulting in a gamete with half the number of chromosomes required for a ‘complete’ cell.  During meiosis, there is a lot of shuffling around and rearranging of the genetic material in the cell.  This is though to be a good thing – it’s one of the ways we have diversity in the population and why we are not carbon copies of our parents.  Unfortunately, however, it’s not a very efficient process and, a lot of the time, nature gets it wrong.  Many of the gametes produced don’t have the correct arrangement of chromosomes so that when they come together to form the embryo, the embryo has a major genetic imbalance.  These little embryos have enough of the right genetic material to get them to the 6 or 8 week mark (or sometimes even later) but not enough that they could ever survive in the outside world. 

The important thing to remember about these miscarriages is that the problem arose, by accident, when the gametes were being made.  In the case of the egg, this was while the woman was herself a fetus.  In the case of the sperm, it was a few months ago.  The outcome for these embryos was, in a sense, preordained.  Nothing that the parents did or didn’t do caused it.  There is nothing they could have done differently to change to outcome.

While this is a genetic abnormality, it’s not the kind of genetic abnormality that is inherited from parent to child.  It’s more correct of think of it as a genetic ‘accident’, and a common one at that. 

When women are diagnosed as having had a miscarriage, they often think that there must be something terribly wrong with them and worry that they will never be able to have a baby.  For the vast majority of women, this is not the case.  They’ve just had some genetic bad luck.

While this type of genetic bad luck can (and does) happen to women of all ages, it becomes more common as women get older – particularly as they approach 40 years of age.

Other Causes of Miscarriage

There are many other causes of miscarriage, all much less common.  We can often get a hint that there is something else going on due to the timing of the miscarriage or the parents’ medical histories.

Abnormalities of the cervix or uterus can cause miscarriage.  These abnormalities may be congenital or as a result of previous surgery.  There are some medical conditions that make women more likely to have miscarriages.  These include autoimmune diseases, connective tissue diseases, and blood coagulation disorders.  Smoking, heavy alcohol use and use of illicit drugs can also cause miscarriage.

Because the common ‘genetic’ first trimester miscarriages are so common, we generally don’t go looking for other causes after a single miscarriage unless there is something in the patient’s history or something about the miscarriage itself that suggests that there could be an underlying cause.  However, if women have recurrent miscarriages, it may be appropriate to investigate further.

Recurrent Miscarriage

The medical diagnosis of Recurrent Miscarriage applies to women who have had three consecutive miscarriages.  Because miscarriage is so common, it’s not unusual for women to have more than one.  Having two or even three miscarriages in a row can just be particularly bad luck and the most likely outcome for these women is that they will go on to have a normal pregnancy next time.  However, once a woman has had more than one miscarriage, we may go looking for an underlying cause.

Some women ask to have these investigations performed after a single miscarriage.  While I can certainly arrange for this to occur, I generally try to avoid investigation until there have been at least two and preferably three miscarriages.  The reason for this is the low likelihood of finding a cause after one miscarriage and the fact that the tests are expensive and will delay you falling pregnant again.  However, please feel free to discuss this with me if you feel very strongly about it.

Investigations may include:

  • Baseline blood tests of your liver and kidneys and other organ systems
  • Blood tests looking for any underlying autoimmune, connective tissue or blood coagulation disease
  • Genetic testing of both parents
  • Ultrasound of the uterus
  • Surgery to better assess the shape of the uterine cavity and the lining of the uterus.
  • Genetic tests on the miscarried embryo

If an underlying problem is found, treatment may be available to reduce the risk of further miscarriage.  This will vary depending on the diagnosis but I will discuss any possible treatments with you in more detail if this situation arises.

Symptoms of miscarriage

The most common sign of a miscarriage is bleeding.  Bleeding in the first trimester is relatively common and many women who experience bleeding will go on to have a normal pregnancy.  If you experience bleeding, you should contact me and I will arrange for you to have an ultrasound to see what’s going on.  The amount of bleeding experienced with a miscarriage is variable ranging from quite light to heavy with clots.  Some women may even pass some pregnancy tissue.

You may also experience crampy ‘period-type’ pain, particularly if you are bleeding heavily

Some miscarriages happen without there being any outward signs.  There may be no bleeding and the miscarriage is discovered during a routine first trimester ultrasound. 

Making the diagnosis

The diagnosis of a miscarriage is usually made on ultrasound.  Sometimes, it obvious that the fetus has passed away.  Sometimes, however, it is not so straightforward.  In very early pregnancies, it can be hard to know whether the pregnancy has failed or whether it is just too early to see the tiny heart beating.  Hormone levels may be useful in this situation although usually the diagnosis is made by repeating the ultrasound after about a week to see whether things have progressed. 

Treating miscarriages

Once the diagnosis is made, there are several options for treatment, depending on your situation.

Generally speaking, the bleeding associated with a miscarriage continues until the uterus is empty.  Sometimes this process is relatively quick  - the pregnancy tissue passes along with the bleeding and the bleeding settles.  These women do not require any further treatment although it is usually worth performing an ultrasound to make sure that the uterus is empty.  Sometimes, however, the process takes a lot longer.

Providing that the bleeding is not too heavy, one option is to wait and see what happens.  Unfortunately, there is no way to predict how long it will take for the pregnancy tissue in the uterus to pass spontaneously or how much bleeding will occur in the meantime. 

Many women chose to have a surgical procedure called a suction curette (or dilatation and curettage or D&C) performed to empty the uterus.  This is done under a general anaesthetic. The cervix is carefully opened up and a small suction catheter is passed into the uterus to gently ‘vacuum up’ all the pregnancy tissue. 

Another option is a medication which causes the uterus to contract and expel the tissue inside it.  This is less commonly used than surgery as it is a bit unpredictable and there is a possibility that women using this medication may need to have and D&C because a small amount of tissue can be left behind in the uterus. It is a good option for women who only have small amount of tissue in the uterus or for those who particularly wish to avoid surgery.

Some women chose to wait a few days or a week to see if the miscarriage will happen on its own, with a back up plan to have a D&C if it does not. 

If you are in this situation, I will discuss the options with you in more detail to help you make the decision that is right for you.

It’s very important to know your blood group when you have a miscarriage.  If you are a negative blood group, you will require an injection of Anti-D to prevent problems with antibodies in future pregnancies – see the Blood Group and Pregnancy information page for more information.

People can underestimate the psychological impact of having a miscarriage.  It is normal to go through a grieving process as you come to terms with what has happened.  If you find that is particularly severe or lasts a long time, you may benefit from help from a counselor.  If necessary, I can refer you to a  psychologist or psychiatrist who has particular expertise in the area of women’s health.

The Next Pregnancy

After the uterus is empty and your bhCG (pregnancy hormone) levels return to zero, your body will ‘reset’ itself and you will ovulate again.  On average this happens after about four weeks which means that you will have your next period after about six weeks (two weeks after you ovulate).  This is just an average – it’s perfectly fine to have your first period a couple of weeks before or after this.  There is no problem with getting pregnant with this first ovulation – your body wont get pregnant before it’s ready too.  However, because this first ovulation is unpredictable, if you do get pregnant before you have a period, it is not usually possible to be certain about your dates.  In the long run, this is not a problem  as we can tell the age of a fetus from it’s size on ultrasound.  However, it can make it harder to interpret an inconclusive ultrasound scan early on in the pregnancy.  For this reason, it is usually recommended that you wait until you have your first period after the miscarriage before trying again.

After a miscarriage, the next pregnancy can be stressful.  You may wish to have a scan performed at six to seven weeks gestation.  We can arrange this for you in the rooms – please feel free to call my receptionist to make an appointment.