Early Pregnancy

Pre-Natal Diagnosis

Pregnancy can be a worrying time. We have the possibility of checking for certain abnormalities.
Not every baby that is conceived is perfect and, in the twenty first century, we have the technology to discover many of those imperfect babies. We use four main techniques:

  • - Samples of mother's blood to measure chemicals
  • - Ultrasound scanning to view certain parts of the baby
  • - Sampling the baby's cells
  • - The mother’s age or family history

Abnormal chromosomes (the structures made of DNA which carry the information that determines what we will be) may produce a recognisable group of physical abnormalities, a syndrome (this means "things that go together"). They are usually named after the doctor who first described them. The commonest of these is an extra number twenty one chromosome making three in all (Trisomy 21). This produces the things which go together to make Down's Syndrome.

What is Screening?

This technique involves testing the whole population, or in this case all the pregnant women to find a number of them who are more likely to have an abnormality and let the others "fall through the screen". A more complicated test (with concomitant risks) may then be used for a small number of women to see if the problem is actually there.
For screening we use chemicals in mother's blood (the double, triple or even quadruple test) and ultrasound scanning. The statistical analysis requires that we accept the result of one test or that we include the results of different tests in the same calculation. It is not appropriate to have one test at one hospital and another later at another.
It is important to remember that screening tests do not give a definite answer to the question "Does my baby have the problem?". They just quantify the chance of something being wrong. A low risk does not warrant further tests (with their risks) but up to a quarter of babies with Down's syndrome will not be picked up by screening and will either miscarry or be born to women who were assessed as having a low risk.

In the First Trimester
A Nuchal fold thickness scan is performed between 11 and 14 weeks of gestation, because the accuracy is best in this period.  The expected thickness depends upon the age of the fetus, so a Crown Rump length will also be measured with the ultrasound

The Nuchal fold is the bright line at the back of the baby's head.




First trimester maternal serum screening can check levels of free β-hCG,PAPP-A, intact or beta hCG, inhibin-A, or h-hCG in the woman's serum, and combine these with the measurement of  (NT). Some institutions also look for the presence of a fetal nasal bone on the ultrasound.

Second trimester maternal serum screening (AFP screening, triple screen, quad screen, or penta screen) can check levels of alpha fetoprotein, β-hCG, inhibin-A, o estriol, and h-hCG (hyperglycosolated hCG) in the woman's serum.

Definitive Testing

Prenatal diagnosis of chromosomal disease involves screening after which an invasive test may be offered

Chorionic villus Sampling (CVS)
CVS involves getting a sample of the chorionic villi (singular is villus) and testing it. This can be done earlier than amniocentesis, but may have a higher risk of miscarriage, estimated at 1%.  It can be performed in a transcervical or transabdominal manner
A small percentage (1-2%) of pregnancies have confined placental mosaicism, where some but not all of the placental cells tested in the CVS are abnormal, even though the pregnancy is unaffected.  Cells from the mother can be mixed with the placental cells obtained from the CVS procedure.
The risk of miscarriage in CVS in about 0.5 - 1%. Apart from a risk of miscarriage, there is a risk of infection and amniotic fluid leakage. The resulting amniotic fluid leak can develop into a condition known as oligohydramnios, which is low amniotic fluid level. If the resulting oligohydramnios is not treated and the amniotic fluid continues to leak it can result in the baby developing hypoplastic lungs (underdeveloped lungs).
Additionally, there is also mild risk of Limb Reduction Defects associated with CVS, especially if the procedure is carried out in earlier terms (before 12th week of pregnancy).

Do I need any preparation?

Your midwife or ante-natal counsellor will have discussed the reasons behind the recommendation. The doctor who is going to perform the operation will discuss it too. It is a very tiny procedure and no special preparation is required other than attending with a full bladder for the ultrasound. If you are very anxious, please talk to your midwife who can reassure you or, perhaps, get a doctor to prescribe something to calm you.

How is it performed?

An ultrasound scan is performed to see where the baby is lying and where there is suitable placental tissue. This may be performed by an ultrasonographer or the doctor. A very fine needle is inserted so that the tip is in the placenta and the scanner is usually used to confirm the position. The needle is so fine that you will hardly feel it. A small volume of the placental tissue is drawn out and sent away for testing.
Afterwards, you are asked to rest for a short while before you go home.


.Amniocentesis
Amniocentesis involves passing a fine needle through your abdominal wall into the amniotic fluid around the baby and drawing out a small quantity for testing.

Why perform an amniocentesis?

Usually, a non-invasive screening test will have been performed which suggests that you are at greater risk than the general population of having a baby with a chromosomal abnormality. Occasionally, there will be another test that is suggested such as a chemical test.
The screening test may be no more than an assessment of your age or your past history. Commonly it will be a blood test often called the "Double test", "Triple test" or even "Quadruple test", or an ultrasound measurement of the "nuchal fold" of the fetus (a fold of skin behind the head).
The purpose of amniocentesis is to identify affected babies so that a termination of the pregnancy can be offered.

Do I need any preparation?

Your midwife or ante-natal counsellor will have discussed the reasons behind the recommendation. The doctor who is going to perform the operation will discuss it too. It is a very tiny procedure and no special preparation is required other than attending with a full bladder for the ultrasound. If you are very anxious, please talk to your midwife who can reassure you or, perhaps, get a doctor to prescribe something to calm you.

How is it performed?

An ultrasound scan is performed to see where the baby is lying and where there is a suitable pool of liquor (fluid around the baby). This may be performed by an ultrasonographer or the doctor. A very fine needle is inserted so that the tip is in the pool of liquor and the scanner is usually used to confirm the position. The needle is so fine that you will hardly feel it. Local anaesthetic can be used to numb the skin but I believe that inserting it hurts more than the procedure. A small volume of fluid is drawn out and sent away for testing.
Afterwards, you are asked to rest for a short while before you go home.

Are there any serious risks?

It is very rare for the mother to suffer more than a little discomfort at the time of the procedure. This may last a day or two but should not need more than paracetamol to relieve it.
Occasionally she might notice a little bruising at the puncture site.
However, for every 100 women who have an amniocentesis, one will miscarry. (A 1% risk). Some of these would have happened anyway as the fetus was abnormal. Some may be caused by the procedure in some way. In our unit at QEII Hospital, our last audit showed that all the miscarriages in the year were, in fact, abnormal.
If you are Rhesus Negative, there is a risk of being immunised against Rhesus positive blood and so you are given an injection of anti-D immunoglobulin following the procedure. This risk was discovered before the days of ultrasound for all. It was common, then, to pierce the placenta (afterbirth). Now that we can see where it is, this risk is probably extremely low.
There is about a 1% risk that fetal cells will fail to grow and no result is possible. A repeat test would normally be offered.

When will I know the result?

If the amniocentesis was done to check the baby's chromosomes, we offer a rapid test (FISH or PCR) which can give a result for Down's, Edward's and Patau's syndromes in about three working days. This type of testing has a small failure rate.
The full Culture result is available in approximately two weeks. This is reliable, but there is a remote possibility (less than 1 in 2000) that it could fail to detect a small chromosomal abnormality.
The length of time needed for certain special tests (e.g. DNA or genetic testing is variable and will be discussed with those individuals who need the tests.


Ultrasound Scanning
This is the definitive test for conditions which are visible.  These include Neural tube defects (Anencephaly, Spina Bifida), limb deformity and other deformities.  Ultrasound of a fetus can sometimes miss subtle abnormalities. For example, studies show that a detailed 2nd trimester ultrasound, also called a level 2 ultrasound, can detect about 97% of neural tube defects such as spina bifida. 

False positives and false negatives

It is important to realise that screening tests are designed with inevitable false positive and false negative results.  The test may predict a low risk of 1 in 1,000 for a problem and no further testing be recommended.  BUT once in a thousand times that result is obtained, the problem will be there.  A high risk of 1 in 250 may cause 249 women to undergo further testing, only to be told that there is not a problem.

We appreciate that waiting for the result can be an anxious and distressing time. We will not intrude, but please contact your midwife or one of the support organisations if you need a talk.

Ante-Natal Results and Choices:
 Website: www.arc-uk.org 
Helpline: 0207 631 0285

Down's Syndrome Association:
 Website: www.dsa-uk.com/frameset.htm
Helpline: 0208 682 4001

Hydatidiform Mole Pregnancies

What is a mole?
Mole pregnancies occur at a rate of approx 1 per 1000 registered births in the UK.
It is known that the pregnancy goes wrong at the time of fertilisation of the egg by the sperm, but we do not know yet why this happens. The afterbirth develops into a mass of fluid filled sacs which give a characteristic picture on ultrasound examination. It looks like a bunch of grapes. It is essentially a benign tumour of the Chorion and so produces abnormally high quantities of human chorionic gonadotrophin (hCG) the hormone that is used for pregnancy tests.

There are 2 types of mole
  1. A "complete mole", in which there is no fetus at any time. Instead the placenta grows as a series of cysts which look rather like grapes (hydatid means watery cyst).
  2. A "partial mole" in which there is evidence of a fetus although it cannot survive.

Treatment
The womb is emptied by suction evacuation. A general anaesthetic is normally used. The operation is somewhat like a hysteroscopy or D&C and the patient can usually go home as a Day Case. The womb can be very soft and it is important that an experienced operator performs the operation because of the risk of perforation.

Follow up screening after evacuation

Patient's serum and urine is tested every 2 weeks until hCG levels are normal, then urine only test every 4 weeks. If a patient's levels reach the normal range within 56 days of evacuation, follow-up will be limited to just 6 months. The Majority of patients with partial hydatidiform mole and patients with lesions suspicious of HM, fall into this short term follow-up group. It also includes some patients with complete hydatidiform mole. For patients who do not reach normal values within 56 days of evacuation, follow-up will continue until 6 months of normal tests have been seen after first normal value.

Patients in the 6 month follow-up group can start a new pregnancy once follow-up is complete. Patients who do not have normal values within 8 weeks of evacuation should have the longer follow-up. After 6 months of normal tests it may be judged reasonable to go ahead with a new pregnancy. In this latter group the risk of choriocarcinoma occurring after hCG has been normal for 6 months is 1:286. Further estimations of hCG, 6 weeks and 10 weeks AFTER ANY FUTURE pregnancies are requested, because of a small increase in risk of choriocarcinoma developing in such patients. In certain cases choriocarcinoma arises from the new pregnancy.
Oestrogen and/or progestogens (e.g. Hormone contraceptives), should NOT be used after any pregnancy until serum hCG results have become normal.
Our patients in South East England are referred for follow-up to the Trophoblastic Tumour Screening & Treatment Centre, situated at:

The Dept. of Cancer Medicine
Charing Cross Hospital
Fulham Palace Road
London
W6 8RF


For more information on Hydatidiform Moles check web link
http://www.hmole-chorio.org.uk/

Miscarriage

Loss of a pregnancy before the age of viability (previously 28 weeks, now 24 weeks) is called a miscarriage in colloquial English. In medical parlance it is termed an abortion.

Types of Miscarriage/Abortion
  • Spontaneous: This started without any attempt to cause it
  • Procured: This may be Legal or Medical or Surgical or Illegal
  • Threatened Abortion: This is the stage before a spontaneous abortion occurs. It usually consists of some vaginal bleeding. At this stage it might resolve (go back to normal), or proceed to
  • Inevitable Abortion: There is the bleeding plus colicky lower abdominal pain. It is just possible that all will return to normal but it usually proceeds to open the neck of the womb (cervix) when it becomes
  • Incomplete Abortion: until all the contents of the womb have been expelled. This is the stage when bleeding can be heavy even to the point of danger.
  • Complete Abortion: When the womb is empty. Bleeding soon stops and after a few weeks, the woman resumes menstruation.
  • Missed Abortion: As we perform more and more ultrasound scans early in pregnancy, we sometimes find that the pregnancy has not developed a fetus, or that a fetus has no beating heart. In these circumstances, the body would soon recognise the pregnancy loss and go through stages 3 to 6.

It is important to realise that most of these losses are a form of natural Quality Control. Though distressing, they are very common and should be accepted. However there are several factors that we have recognised as making miscarriage more likely. So if a woman has several miscarriages in a row, she should seek investigation for. . .

  • - Recurrent Abortion: It is probably worth investigating if three occur at a similar time in the pregnancy (i.e. they might be due to the same cause).

Recurrent Miscarriage / Abortion
To lose a much wished for pregnancy is a great distress.  To miscarry repeatedly is devastating.  Many miscarriages are, in effect, quality control and a chromosomal or other abnormality is found in the fetus.  For many years we did not know any other reasons for miscarriage.

Recurrent miscarriage is defined as suffering three or more miscarriages without a term pregnancy intervening.  This number makes it much more likely that there is a reason for us to find.

Why does miscarriage happen?

Most miscarriages represent quality control. The embryo must reach a series of milestones and if it fails, it is ejected. However there are a number of maternal diseases or conditions that are known to cause miscarriage.
Infections:       Milkmaids who were infected with cowpox gained immunity from Smallpox leading Jenner to develop variolation and then vaccination (a beneficial result of infection). Shepherdesses, however, were exposed to infection from their sheep with Brucella abortus and suffered more miscarriage than others. These diseases are (practically) never seen these days. There is little or no evidence that infection is a major cause of recurrent abortion. Acute infections of many types will cause abortion (malaria, rubella, listeria etc.) but the body will usually develop immunity preventing recurrence due to the same cause.
Genetic causes:       If mistakes are made in copying genes during production of egg or sperm, a good ‘mutation’ may sometimes happen but the vast majority of these mistakes will be harmful. These mistakes range from extra chromosomes: three rather than the normal pair of the number 21 chromosome (trisomy 21) produces Down’s Syndrome. . . . through rearrangements of parts of chromosomes (which might not have any clinical effect and in fact be present in either parent). . . to mutations of individual genes (some of which we now recognise and can test for). Genetic abnormalities are found in about 5% of recurrent abortion.
Anatomical causes:        In order to conceive at all, the mother must have pretty normal uterus, Fallopian tubes and ovaries. Abnormality of the cavity of the womb may, however, interfere with implantation (settling into the lining of the womb by the embryo). A polyp may act a bit like a contraceptive coil. A septum in the womb (a wall down the middle like the nasal septum in the nose) may have poor blood supply and not nourish the embryo properly. A fibroid under the lining might do the same. A bicornuate uterus, so called because it has two ‘horns’, may be present. The womb is formed from two tubes which sometimes do not fuse properly. This typically produces a picture of pregnancies that last a bit longer each time as the ‘horn’ of the uterus is stretched a bit more with each pregnancy.
Hormone Problems:   A woman needs all her control mechanisms working properly. Any endocrine (hormone) disease may produce miscarriage. Usually it will be severe enough to diagnose and will commonly be associated with failure to conceive. Diabetes mellitus may not have been diagnosed. Poor control can give a raised rate of miscarriage and fetal malformation. Good control of blood sugar before and in early pregnancy can bring this back to normal.
Autoimmune disease:    Certain diseases in which the body’s defence mechanisms attack our own bodies are called ‘auto-immune’. (Perhaps the most well known is rheumatoid arthritis) We find some evidence of autoimmune disease in about 10% of recurrent abortion. “Rhesus auto-immunisation” is not strictly an autoimmune disease as the rhesus positive woman develops antibodies to rhesus positive blood which then attack her fetus (not herself). It usually presents as a problem of late pregnancy and will normally have been recognised before it becomes a cause of recurrent miscarriage.

Retroverted gravid uterus

The uterus (womb) is held steady in the pelvis by ligaments at the level of the cervix (neck of the womb). This means that the body of the uterus can flop backwards and forwards. When the bowel is full and the bladder is empty, it flops forward and is said to be anteverted. The opposite is called retroverted and between the two is axial. It is more common to find, on examination, the uterus to be anteverted (60 – 80%). Some women seem to have a uterus which is always retroverted. This is normal and if one conceives in a retroverted uterus it will become axial as it grows. There is no evidence of an increased risk of miscarriage. However, on rare occasions, the retroverted uterus does not slip into the correct position and becomes stuck. This is termed an incarcerated retroverted gravid uterus. In this circumstance, there is intense pain. The urethra (tube carrying urine from the bladder) is stretched and sometimes blocked by pressure preventing passage of urine. This is a medical emergency and requires drainage of the urine. A doctor may be able to correct the position manually. Sometimes, there are no symptoms and the uterus grows to accommodate the growing fetus by expanding the anterior wall while the top (fundus) remains in the pelvis. Sometimes, it cannot expand and a miscarriage occurs.

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