The risks of miscarriage
The term 'miscarriage' describes the loss of a baby during the earlier weeks of pregnancy and is something that affects many women. Losing a baby through miscarriage is a heartbreaking experience, no matter how early in the pregnancy it happens, usually rousing deep feelings and emotional reactions.
In New Zealand, miscarriage is defined as a baby who dies before 20 weeks gestation and/or less than 400 grams in birth weight. Babies who die after 20 weeks gestation (or who weigh more than 400 grams) are classified as being stillborn. This definition is not applied worldwide. The World Health Organisation (WHO) defines miscarriage as being up to 23 weeks of the pregnancy and 500 grams in weight, and other countries define miscarriage as up until 24, 26 or 28 weeks of pregnany. The definition of a miscarriage is also usually divided up into 'early miscarriages' (before 13 weeks) or 'late miscarriages' (after 13 weeks and before 20 weeks). About 80% of miscarriages will occur before 12 weeks.
When is the risk of miscarriage highest?
The risk of miscarriage is highest immediately after the fertilised egg implants. It is thought that around 50% of all fertilised eggs do not survive, coming away with a normal (or slightly late) period. This is often referred to as an 'unnoticed miscarriage' because it is usually not formally acknowledged by the pregnant woman, who is never aware of her pregnancy.
It is estimated that about 15 to 20% of known pregnancies will end in miscarriage. This statistic is often received with surprise and shock, equally because of its high prevalence as well as how little it is acknowledged and talked about openly.
While a miscarriage can happen at any time during the first 20 weeks of pregnancy, they more commonly occur around the times the woman's subsequent periods would have been due. That is around 4, 8 and 12 and 16 weeks of the pregnancy.
I have had a miscarriage already - will I have another one?
Women who experience one miscarriage are not more likely to experience another (unless they have a medical condition that is likely to cause recurrent miscarriages). Up to 97% of women who experience one miscarriage will go on to have a healthy baby with a subsequent pregnancy and up to 75% of women who have had 3 or more miscarriages will have a subsequent normal pregnancy and baby.
Reasons for miscarriage
During the first 12 weeks of pregnancy, an intricate and complicated process takes place as the woman's egg is fertilised and implants, develops and grows. It is thought that up to 50% of miscarriages are due to a spontaneous genetic or structural abnormality, with most of these occurring at the time of fertilisation. This can cause the foetus to not develop properly, or to die after only a few weeks of the pregnancy. If the baby does not continue to thrive and grow, in most cases the woman's body will naturally expel the baby through miscarriage. It is for this reason that many people believe miscarriage to be 'nature's way' of ending a pregnancy that would otherwise have led to a baby being born with major abnormalities.
Although miscarriage is very common, for the majority of women the cause of their miscarriage will remain unknown. Even with the many advances in medical technology in recent decades, there is still much we do not know about the loss of a baby through miscarriage. This lack of information and 'not knowing' why your miscarriage has occurred can make dealing with it very difficult.
The question of "Why me?' will often bring up feelings of frustration, helplessness, guilt and doubt about your body's ability to carry a baby, as well as much fear and anxiety about future pregnancies.
If the miscarriage cause remains unknown, it is important to remember that it is very rare for a woman to miscarry because of something she may or may not have done. This can be hard to accept when coming to terms with losing your baby, because it is very common for women to search for reasons as to why they may have miscarried. Feelings of guilt can be reinforced by friends or relatives suggesting a 'reason' for your miscarriage. (Probably based more on myth and folklore, rather than a real medical cause.)
Guilt and self blame are very common reactions to miscarriage. These will often be felt no matter how much caregivers try to reassure you that your actions (or inactions) were not responsible for you losing your baby. Many thoughts can cross your mind, "Was it because I did not rest enough, or had that glass of wine, or had a cold, or was working too hard or didn't start my folic acid tablets? Did I cause this miscarriage?' These feelings are distressing, but a very normal part of the grief and loss.
There are a few known medical causes of miscarriage. This can account for a further small percentage of miscarriages, as well as the cause of some recurrent miscarriages (where the woman experiences 3 or more miscarriages in a row). Occasionally, tests can be done to determine a medical cause, but in the majority of cases no cause will be found.
Medical causes of miscarriage
Sometimes there are medical causes for miscarriage that may explain for a few women why their miscarriage has happened. Identifying a reason (if this is possible) can often help you come to terms with it better, because it may work towards assisting you in avoiding another miscarriage in the future. Medical reasons may include:
- An infection of the uterus during early pregnancy.
- Other viral or bacterial infections during early pregnancy, such as rubella and Listeria
- Medical interventions to detect abnormalities in the baby. A CVS (done between 10 to 12 weeks) or an amniocentesis, (done between 14 to 18 weeks) can increase a woman's risk of miscarrying her baby.
- A weakened cervix that can allow the cervical muscle to spontaneously open, usually between 14 and 28 weeks of the pregnancy. This is known medically as 'cervical incompetence' and in some cases is treated with a'stitch in the cervix'.
- If the baby implants on an area of the uterus where there is a very large fibroid, the blood supply may be diminished to the baby and unable to support their continued growth.
- Trauma (such as a serious car accident), or a blow to the woman's lower stomach.
- If the woman needs abdominal surgery during the first 20 weeks of pregnancy.
- An unusual shaped uterus. A few women are born with this, increasing their chances of miscarriage after 12 weeks of the pregnancy.
- Environmental exposures to certain drugs or prescribed medications, smoking, excessive alcohol, radiation, certain chemicals and pesticides.
- Health conditions such as autoimmune diseases (for example Lupus), blood clotting disorders, diabetes, hormonal imbalances, kidney disease or low thyroid function. These may be the reasons for 'recurrent' miscarriages, meaning 3 or more consecutive miscarriages. However, when some of these conditions are treated or well controlled, the chances of miscarriage will tend to be no greater than any other healthy woman.
- Increased age. The incidence of genetic abnormalities increases with the woman's age. Miscarriage rates are about 10% for women in their 20's and up to 50% for women over 40. There is also some recent research that implicates a man's increased age as also being a possible factor for miscarriage.