Miscarriage is common. When miscarriage happens early in pregnancy, some well-meaning people will say it's for the best that it happened sooner rather than later. This does not acknowledge the loss of a pregnancy. When a woman finds out that she is pregnant, it can set up an image of a life-long future with a child. When this image is taken away unexpectedly it is a lot to grieve for. After a miscarriage, it takes time to recover psychologically.
Miscarriage is neither causable nor preventable. If a miscarriage is going to occur, it will happen whether there is strict bedrest or whether normal activities are carried out.
Over 20% of all pregnancies will end in miscarriage. After a reassuring Nuchal Translucency Screen the risk of miscarriage is less than 2%. After 16 weeks the risk of loss of the pregnancy is between 1 in 100 and 1 in 1000.
Symptoms of Miscarriage
Some miscarriages occur so early that a normal period may follow a positive pregnancy test. Traditionally, a spontaneous complete miscarriage refers to an episode of heavy bleeding and cramping pain at which time there is passage of the fetus and placenta. Symptoms of bleeding and pain can be distressing. Presentation to hospital may be needed for intravenous fluids, analgesia and sometimes curettage if the symptoms are not resolving.
Most miscarriages are now diagnosed on ultrasound scanning as non-viable pregnancies before there are significant symptoms. An early ultrasound scan for dating of the pregnancy may show that the pregnancy is behind the expected dates. A follow-up scan may show that there has been no further growth and a non-viable pregnancy is diagnosed. When there is bleeding and pain in early pregnancy an ultrasound scan may detect a non-viable pregnancy where the fetus has no heartbeat. Some non-viable pregnancies are found at an antenatal visit or at a routine scan appointment.
Causes of Miscarriage
There are two main causes for miscarriage. One is due to a problem with the genetic material. The other is due to a problem with the formation of blood vessels within the placenta which supplies the fetus with oxygen and nutrition.
Genetic Causes of Miscarriage
The fetus may not have the right number of chromosomes in its cells. This can happen if there is an abnormal number of chromosomes in an egg or sperm, or an egg may be fertilized with two sperm at the same time. Sometimes the chromosomes in the embryo are normal and problems occur with early cell divisions. Genetic material is meant to be duplicated exactly and divided equally into the new cells that are forming, so that each cell has the same number of chromosomes. This process can be inaccurate so that some cells will have too many chromosomes and some cells will not have enough chromosomes. Inaccuracy can increase with maternal age.
The embryo can grow with abnormal chromosomes but the development of organs may fail due to insufficient genetic material in every cell. The fetus will fail to establish a heartbeat. The absence of a fetal heartbeat can be used to diagnose a non-viable pregnancy. Sometimes the fetus will stop growing and shrink down leaving just an empty sac. Absence of a fetal pole can diagnose a non-viable pregnancy.
The fetus may continue to develop with an extra chromosome in its cells. In Down Syndrome, cells have a third copy of chromosome 21 or Trisomy 21. Other common Trisomies are an extra Chromosome 18 or Chromosome 13. Turner's Syndrome has an absent X chromosome making the fetus XO instead of the normal female XX. With these conditions the fetus can suffer demise in utero at any stage during pregnancy. Babies have been born with Trisomy 18 and lived for some years but never develop normally. Babies born with Down Syndrome or Turner's Syndrome may have significant health issues but may have a reasonable quality of life.
The Nuchal Translucency Screen around 13 weeks gestation and the Non-Invasive Prenatal Test were designed to detect abnormalities in Chromosomes 21, 18, 13, X and Y. If these screening tests suggest there may be a problem with the chromosomes, this can be confirmed prior to delivery with invasive testing. Fetal cells collected with a needle from the placenta (chorionic villus sampling) or from the amniotic fluid (amniocentesis) can be grown in culture. All of the chromosomes in these cells, not just the common trisomies, can be checked for abnormalities. Depending on the findings, genetic counselling may be needed to consider how baby may be affected.
Placental Causes of Miscarriage
Sometimes the blood vessels in the forming placenta may not develop properly or they may become blocked with blood clot. This can stop blood supply to the fetus and lead to fetal loss. Abnormalities in placental vessels are more likely to occur in maternal medical conditions such as clotting disorders, thrombophilia, autoimmune diseases and diabetes. Poor formation of placental vessels may not result in miscarriage but may cause problems later in the pregnancy. This may include poor fetal growth, bleeding behind the placenta and or the hypertensive disease of pregnancy (pre-eclampsia).
Management of a Non-Viable Pregnancy
If a non-viable pregnancy is detected there are three options: waiting for spontaneous miscarriage to occur; medical management; or surgical management.
Eventually a non-viable pregnancy will miscarry with bleeding and sometimes pain depending on the size of the fetus. Non-viable pregnancies may take a long time to resolve. In the days when the only routine scan was at 20 weeks, it was not uncommon to find a 6-week non-viable pregnancy still present in the uterus at 20 weeks gestation. Eventually a non-viable pregnancy will be passed and this may occur with exertion, hence the old wives tale blaming exertion for miscarriage. It is not likely for exertion to cause a viable pregnancy to be expelled. Some women who elect to await spontaneous resolution of their non-viable pregnancy will become tired of waiting after a few weeks and will consider other management.
Medical management speeds up the process of the uterus expelling the contents. Doses of the prostaglandin Misoprostol, sometimes in combination with the antiprogestogen Mifepristone, can make passage of the fetus and placenta occur. This medication will work in about 85% of pregnancies. Sometimes the non-viable pregnancy will remain in the uterus and surgical management may be needed.
With the passage of fetus and placenta there may be an episode of heavy bleeding and crampy abdominal pain which is usually self-limiting. Sometimes these symptoms will continue and require admission to hospital for analgesia, fluids, and emergency curettage to stop the bleeding and pain. Some women prefer to avoid this process and will opt for surgical management.
Suction Curettage or Dilatation and Curettage
Surgical evacuation of a non-viable pregnancy will usually return menstrual cycles to normal more quickly than waiting or medical methods. Any tissue that is removed from the uterus is sent to be looked at under a microscope. There are some very rare conditions called Gestational Trophoblastic Disease where there are abnormal cells in the placenta. If this is diagnosed then the hormone of pregnancy needs to be followed up with regular blood tests after the miscarriage to make sure levels return to zero. This ensures that no abnormal placental cells remain within the body. The Chorionic Villi of the placental tissue can be sent for Cytogenetics. Tissue is grown in culture so the chromosomes in the cells can be investigated. This may detect chromosomal abnormalities which confirm a genetic cause for the miscarriage.
General Anaesthetic is required for curettage. There are small risks from a General Anaesthetic and for the first 24 hours after the General Anaesthetic, driving and any responsibility should be avoided. Usually 48 hours of recovery would be required.
Prior to the procedure it is necessary to abstain from food for 6 hours and water for 2 hours. In theatre the anaesthetist will insert a cannula and give intravenous fluids. Oxygen will be given through a face mask. Anaesthetic will be delivered intravenously and through the mask. General Anaesthetic will be in effect for approximately 20 minutes and the procedure will take around 15 minutes.
Once the anaesthetic is working, the legs will be lifted into lithotomy position. The vaginal area will be prepared with antiseptic solution and drapes will be placed over the legs. The bladder is emptied by catheterization. The size of the uterus is estimated by bimanual examination and passing a measuring sound through the cervix.
The cervix is designed to dilate and is always slightly open. Stainless steel dilators are used to push the cervix open from the inside. The dilators are graduated in size so that the cervix will be opened to approximately the diameter of a pen. This is the dilatation part of a dilatation and curettage.
An angled piece of tubing attached to suction can be used like a tiny vacuum cleaner to evacuate the pregnancy sac from the uterus. Checking that the cavity is empty can be performed with a curette. This instrument is a blunt metal ring with a sharp inner edge. When this is angled against the inside of the uterus it combs the lining of the uterus and removes any fragments of tissue or blood clots. These processes are continued until no further tissue is obtained from the uterus.
Possible Complications of Surgical Management
With any operation there is a risk of infection. There may be a small risk of infection with a passage of a non-viable pregnancy spontaneously or after medical management. The risk is slightly greater with surgical management but a preventative dose of antibiotics can be given at the time of the procedure.
After the procedure there will be some bleeding like a period. Sometimes there is hardly any bleeding for a few days until the hormone of pregnancy falls and then a period will start. Over time the bleeding should gradually lessen and should be reduced to blood stained mucus or spotting by the third week. Infection is common in the second week after the procedure and may cause symptoms of heavy bleeding, pain, fever, offensive discharge or persistent heavy bleeding into the third week after the procedure. If these symptoms occur, then a course of antibiotics can be given orally. If there is very heavy bleeding, extreme pain and fever, intravenous antibiotics or a repeat curettage to remove infected blood clot may be required.
The risk of requiring a blood transfusion at the time of a curette is small. If there is severe infection a few weeks after the procedure, then heavy bleeding at this stage could result in significant blood loss. The risk of needing a blood transfusion is increased if there has been a history of heavy or prolonged bleeding prior to the curette, or if the haemoglobin is low.
Perforation and further surgery
Anytime instruments are put inside the uterus there is a small risk of perforation or creating a hole in the wall of the uterus. This occurs in less than 2% of curettes. Usually a perforation will heal without causing any problems. If perforation occurs, a course of oral antibiotics may be given as a precaution to prevent spread of any infection. Perforation is more likely to occur at the end of the procedure when the uterine cavity is being checked for any remaining tissue or clots. If the perforation occurs prior to removal of all the tissue, it may be necessary for a laparoscopy, or key hole surgery, so that a camera placed in the abdomen can see the curette completed under vision.
If there is a perforation there is a risk of damage to bladder and bowel and if the curette keeps passing out through the hole in the uterus, then this increases the risk of damage to other structures. Requirement for a laparoscopy occurs in 1 per 1000 curettes. Further surgery to repair damage to the uterus, bladder or bowel can be performed through key hole surgery. For 1 in 10,000 curettes, further surgery will require an opening into the abdominal cavity, or laparotomy, for repair of uterus, bladder or bowel. Rarely, if there is a large perforation of the uterus, especially at the top, then there is a risk of this scarred area rupturing during labour, and a Caesarean Section may be recommended for a subsequent delivery.
It is possible for scar tissue to form across the inner part of the cervix. This is called cervical stenosis and after 1 per 1,000 curettes, the scarring can be so severe that it stops menstrual blood coming out in future periods. If this occurs dilatation of the cervix to break down the scar tissue may be required at a Cervical Screening test or under anaesthetic. It is also possible for the cervix to be weakened by the curette process so that it is opens up too early in a future pregnancy. This is called cervical incompetence and occurs after 1 per 10,000 curettes. If cervical incompetence is detected on early scanning in a future pregnancy it is possible to put a suture around the cervix to prevent further shortening or opening of the cervix during pregnancy.
After two or more miscarriages further investigations can be carried out to exclude conditions that could be managed. Genetic causes are usually random but the chromosomes of the potential mother and father can be tested for any chromosomal abnormalities that are likely to occur again in future pregnancy attempts. Sometimes assisted reproduction with in vitro fertilization can increase the chances of an ongoing pregnancy. If several eggs are fertilized at one time, then the successful embryos which appear unaffected by abnormal chromosomes can be transferred into the uterus.
Screening blood tests can be performed on the mother to exclude thrombophilia, autoimmune disorders, pre-existing diabetes and thyroid conditions. Some of these conditions can be treated to maximize the chances of successful pregnancy. Development of blood vessels in the placenta may be enhanced by taking low dose Aspirin (100 mg daily) after the diagnosis of pregnancy. If conditions like antiphospholipid syndrome or anticardiolipin antibodies are detected, then injections of Clexane in early pregnancy may improve development of the placental vessels. If auto-antibodies are at high levels then they can sometimes be lowered by the use of the steroid Prednisone in early pregnancy to decrease antibody production. Prior to assisted reproduction, mechanical causes of early miscarriage may need to be diagnosed and managed. This may involve a hysteroscopy where a telescope inserted inside the uterus will show if there are any fibroids or an abnormal septum in the uterus which might reduce the ability of an early pregnancy to implant and grow.