miscarriages - Introduction

A miscarriage (also known as abortion) is a pregnancy that ends before the baby can survive outside the womb because it has not yet reached viability. A miscarriage may be early  - during the first 14 weeks of pregnancy, or late. The vast majority are early - only about 1% of miscarriages are late.

The definition of a miscarriage is a spontaneous loss of a pregnancy before 24 weeks: in the UK we calculate the duration of a pregnancy from the first day of the last period (LMP). A miscarriage - the medical term for an early pregnancy loss is abortion - tends to start with bleeding, and pain may then develop. Sometimes there may be bleeding early in the pregnancy but the pregnancy continues (threatened abortion). An inevitable abortion means that the pregnancy cannot be salvaged. It may be incomplete, with pregnancy products still in the cavity of the womb or complete with nothing remaining.

The combination of modern pregnancy tests and ultrasound will usually determine the situation quite quickly. Pregnancy tests these days should become positive within ten days of conception (i.e. even before the first missed period). Ultrasound begins to show a pregnancy within the uterus by five or six weeks (a week or two after the first missed period). On occasion, it may be too early to diagnose the situation accurately and tests may need to be repeated to see what changes occur.

Types of miscarriages

Table 12.1 indicates the various terms most frequently associated with miscarriages.

 
Type of miscarriages Description
Spontaneous miscarriages This is when the miscarriage occurs naturally as opposed to being induced.
Induced miscarriages The pregnancy is terminated artificially.
Threatened miscarriages There is bleeding and sometimes pelvic pain but the cervix is closed and ultrasound indicates an ongoing pregnancy within the uterus.
Inevitable miscarriages The pregnancy is not continuing.
Complete miscarriages An inevitable miscarriage and the uterus has completely emptied itself.
Incomplete miscarriages An inevitable miscarriage with products of the pregnancy still present in the uterus.
Missed miscarriages There are no reasons to have suspected that the pregnancy is not going to continue but the embryo has died.
Septic Miscarriage The miscarriage has been complicated by infection.
Recurrent or habitual miscarriages Most authorities recommend that these terms should be used only for three or more consecutive miscarriages although there is a tendency towards two.
Early miscarriages miscarriages in the first few weeks of the pregnancy.
Late miscarriages miscarriages after the first few weeks.
First trimester miscarriages miscarriages before thirteen weeks of pregnancy.
Second trimester miscarriages miscarriages after thirteen weeks and before twenty four weeks.

miscarriages symptoms

The first miscarriage symptom is vaginal bleeding, which can range from spotting to being heavier than a period. A little spotting may be an early sign of miscarriage although fortunately this may amount to no more than a threatened miscarriage and the pregnancy continues. The second miscarriage symptom is pelvic pain. The third miscarriage symptom is cessation of pregnancy symptoms including breast tenderness, morning sickness and having to pass urine more frequently than usual. Some women have no miscarriage symptom and the discovery is made at ultrasound examination.

Sometimes there may be no sign or symptom to suggest miscarriage and pregnancy symptoms continue, and the miscarriage is only discovered in a routine scan. This is a missed miscarriage. A threatened miscarriage occurs when there is vaginal bleeding but ultrasound confirms a viable pregnancy.

Cause of miscarriages

Often the cause of a miscarriage remains unknown. The most common cause for miscarriages is a blighted ovum ? the afterbirth type tissues develop but there is no baby. Another common cause is a genetic defect and nature decides not to allow the pregnancy to continue. Smoking and obesity may contribute to miscarriages but do not cause miscarriages by themselves. Similarly,  stress may play a role in pregnancy loss, but it hasn't been shown to cause miscarriages on its own. Cause for recurrent miscarriages is discussed Q12.16 to Q12.21.

Prevalence Of miscarriages

It is thought that between 10 and 20% of pregnancies miscarry. Most miscarriages occur in the early weeks of pregnancy. Ultrasound screening for fetal anomaly has shown the incidence of non-viable pregnancy at 10-13 weeks to be 2.8%

Blighted Ovum

Normally the fertilised egg divides and part becomes the embryo (future baby) and part becomes the afterbirth type tissue (trophoblast) and the membranes that form a fluid filled bag around the baby. When there is a blighted ovum, the afterbirth tissues develop alone without the development of the baby. Blighted ovum hasalso been referred to as an 'anembryonic pregnancy'. Nearly half of early miscarriages are associated with a blighted ovum. It is likely that abnormal chromosomes are more prevalent.

 

Hydatidiform Mole

This is a benign tumour of the trophoblast (afterbirth tissues) characterised by vesicles which look like small grapes. Usually a hydatidiform mole develops without an embryo but this is not always the case. As hydatidiform moles produce a relatively high level of the pregnancy hormone HCG, there tends to be an increased incidence of excessive vomiting in early pregnancy. The diagnosis is usually made from the typical ultrasound picture. The womb will need to be carefully emptied by suction. Very rarely, there is subsequently evidence of malignancy (choriocarcinoma). It is therefore essential that you are carefully monitored for a few months by hormone tests on your urine. These days choriocarcinoma can be treated successfully by chemotherapy (Q32.33).

Pictures of a hydatidiform mole from www.hmole-chorio.org.uk

Picture of Hydatidiform Mole

antibodies circulating in their blood that target their own body tissues. Examples of autoimmune diseases include:-
  • systemic lupus erythematosus,
  • Sjogren syndrome,
  • Hashimoto thyroiditis,
  • rheumatoid arthritis,
  • juvenile (type 1) diabetes,
  • polymyositis,
  • scleroderma,
  • Addison disease,
  • vitiligo,
  • pernicious anemia,
  • glomerulonephritis, and
  • pulmonary fibrosis.

There are two issues to consider in the context of a possible autoimmune causation of recurrent pregnancy loss the antiphospholipid antibodies and alloimune pregnancy loss.

Lupus anticoagulant and anticardiolipin are two antiphospholipid antibodies that have been associated with miscarriage. They increase the chance of the blood clotting (throbophilia - Q12-12) and this may damage the placenta . When they are present, and not treated, a live birth can only be expected in 25-50% of subsequent pregnancies. Scientifically controlled trials have demonstrated that low-dose aspirin in combination with heparin will increase the chance of a live birth in women with antiphospholipid antibodies. Many women have taken low dose aspirin in pregnancy apparently without problems. There is no evidence so far that low dose aspirin treatment will improve the outcome if there is no increased antiphospholipid antibodies although in one study involving IVF, low dose aspirin enhanced treatment outcome even in the absence of these antibodies.

In the era of blood transfusion and organ transplantation, we have all become aware of the importance of tissue typing and the problems of the immune response, which limits our choice of donors. In general, tissue typing is likely to show that a child could not donate an organ to its mother. In this context, it is remarkable that during pregnancy the baby is not rejected by the immune system even though the baby's blood comes into direct contact with maternal tissue in the placenta (afterbirth). The immune system is known to change in pregnancy and there must be some adaptation to allow the majority of pregnancies to continue. It has been suggested that some women who recurrently miscarry have a defect in this normal immune adaptation (alloimune pregnancy loss).

One method of treating women with recurrent miscarriage seeks to alter their immune response by immunising them with white blood cells obtained from their partners. It is still uncertain whether this treatment increases the live birth rate. One meta-analysis (Q33.23) suggests that there may be a 10% improvement. If it has a benefit it may be appropriate only for those who are deficient in the relevant antibody (APCA) and also those with a relatively high number of pregnancy losses.





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