Mid trimester miscarriages

These are rare and are usually due to an abnormality of the mother’s womb – in particular a weakness of the neck of the womb They may also be caused by irregularities in the shape of the womb.

Why cervical incompetence causes miscarriage

Normally the circular muscle fibres of the cervix remain tightly closed throughout pregnancy and act as a barrier to prevent the baby ‘escaping’ from the womb. However, if the cervix is weak it is slowly stretched open by the weight of the developing foetus until it’s no longer efficient enough to contain the contents of the womb. Most miscarriages due to cervical incompetence take place at about the 16th week of pregnancy, when the cervix has become so dilated that the developing baby simply ‘falls through’. An incompetent cervix is almost impossible to predict in advance and is usually only discovered after a miscarriage has occurred. The most common cause is overstretching the cervix muscles, cither during a previous D and C or termination of pregnancy operation, or during a particularly difficult or rapid labour when the baby is unduly large. Very occasionally it can simply be that a woman is born with an inherent weakness of the neck of the womb. However, it’s a fact that very few women suffer from an incompetent cervix where there is no history of previous operation or pregnancy. In the case of a woman carrying twins, however, the weight of the babies can be enough to dilate the cervix and so cause miscarriage.

Recognizing a mid-trimester miscarriage

Regardless of cause, miscarriages in the second three months of pregnancy often occur rapidly and without much warning. Bleeding may sometimes occur beforehand, but often the first a woman knows about the miscarriage is when the membranes surrounding the baby rupture and the waters break. This can happen anywhere and at any time and is often extremely embarrassing for the woman. Wherever she is, it’s important that she finds somewhere to lie down and a doctor is called. If this isn’t possible then someone should call an ambulance and get her to hospital. Unfortunately, once the waters break, the miscarriage is virtually inevitable.

The foetus is often expelled quite quickly, usually within a matter of hours. Although stomach cramps may sometimes accompany it, the miscarriage is normally relatively painless.

In most cases a D and C will be carried L-out and the womb will be carefully explored in order to find a possible cause for the miscarriage. If it doesn’t reveal an obvious cause, your doctor will probably test the strength of the cervix a few weeks later when things have settled down again. This will be done by gently attempting to insert a rigid rod of a certain critical diameter into the cervix. If it passes easily down the cervical canal it indicates that the cervix is weak.

If this is the case, treatment is straight-forward and future prospects for achieving a full-term pregnancy are very good. When the woman becomes pregnant again the doctor will advise that the cervix is strengthened by placing what’s called a ‘purse string stitch’ around it. This is then pulled tight to keep the cervix firmly closed. The stitch is put in under general anaesthetic when the woman is about 14 weeks pregnant. It is removed at about the 38th week of pregnancy by a simple, painless procedure which does not require a general anaesthetic.

A D and C after a mid-trimester miscarriage may reveal, or lead the surgeon to suspect, that the woman has an abnormally shaped uterus. This is commonly due either to a septum, or to fibroids. Either possibility may subsequently be confirmed by a special X-ray test of the womb, called a This involves injecting a special radio opaque dye through the cervix into the womb cavity. When the X-ray is taken, the dye casts a shadow outlining the shape of the womb cavity on to the X-ray plate, thereby revealing any abnormalities.

After three mid-trimester miscarriages have occurred in a woman with this unusual feature.


These are swellings of muscle and fibrous tissue in the wall of the uterus which may sometimes protrude into the womb and distort its shape. They do not necessarily cause miscarriage; indeed many women who suffer from fibroids achieve full term pregnancies, but their existence does increase the risk of miscarriage. This can be because unequal stretching of the womb wall tends to induce contractions and the early expulsion of the baby. Alternatively, the distortion of the womb wall may cause the placenta to become detached and so induce miscarriage.

If the fibroids cause miscarriage they can later be dealt with by an operation called whereby each fibroid is removed individually. There is then no reason why subsequent pregnancies should not run to full term.


This is a wall which cither partially or completely divides the uterus in two. As in the case of fibroids, this uterine abnormality does not necessarily mean abortion is inevitable. However, if a septum causes a miscarriage, treatment is much more difficult since extremely complicated surgery is required to correct this condition. In fact, the operation is rarely performed.

Placental insufficiency

There is also a condition, known as which may affect a small proportion of babies. It usually begins to develop in the 24th to 26th week of pregnancy, but does not become an obvious problem until after the 28th week – during the last three months or of pregnancy.

If a normal healthy baby is to be produced it’s obviously vital that the placenta functions efficiently. In the case of placental insufficiency the placenta grows slowly and fails to mature properly. It is therefore unable to provide adequate nourishment and oxygen for the developing baby.

Although the foetus matures normally it is much smaller than it should be after 28 weeks of pregnancy, simply due to lack of nourishment. Placental insufficiency may in some cases become so severe that it can no longer supply the baby’s basic requirements. The foetus may then die in the womb and be expelled as stillbirth.

However, in many instances placental insufficiency is recognized and may be treated in time to prevent the foetus being lost.

Smoking is a common cause of placental insufficiency and in this case obviously the best treatment is to try to give up the habit. It may also occur in pregnant women suffering from toxaemia, or alternatively it may occur for no apparent reason at all. In these last two instances, bed rest may help the pregnancy run to full term and prevent a miscarriage.

Becoming pregnant again

It’s usually advisable not to try for another pregnancy until at least three menstrual periods have elapsed. (The first menstrual period usually occurs four to six weeks after a miscarriage although a larger interval is not uncommon.) This will ensure that the lining of the womb is suitable to receive a fertilized egg, and it will also establish a definite date for the last period, from which the expected date of deliver can be accurately calculated. If a woman conceives directly after a miscarriage it may be difficult to calculate the ovulation date and so virtually impossible to give an accurate expected date of confinement.