Pregnancy

Pregnancy occurs when a sperm penetrates an egg. The single sperm that first burrows into the egg is the successful one of millions of others contained in the man's semen. This is called fertilisation, and usually takes place in the woman's fallopian tube after the matured egg has been released from one of her ovaries (ovulation).

Sperms may contain an X chromosome or a Y chromosome. If an X fertilises, the result will be a girl; if a Y penetrates, the result will be a boy. Sperms and eggs each contain 23 chromosomes, and the total number required of 46 chromosomes is achieved when a sperm and egg fuse at fertilisation.

The fertilised egg immediately begins to divide into a growing cluster of cells. Between five and seven days after ovulation, the fertilised egg implants into the wall of the uterus and produces root-like outgrowths called villi. These help to anchor it to the lining of the uterus and will eventually grow into the placenta, the organ that feeds and protects the baby until birth.

The placenta maintains and nourishes the baby by enabling the transfer of oxygen, carbon dioxide, amino acids, fats, vitamins and minerals from the mother's blood. It also allows the transfer of waste substances from the growing baby.

From the time of implantation into the wall of the uterus until approximately the eighth week of life, the baby is known as an embryo. Development is rapid during this stage, as specialised cells begin to form the vital organs, nervous system, bones, muscles and blood. After the eighth week of pregnancy, the developing baby is called a foetus. It is about 2.4cm long, with most of the internal organs formed. External features such as the eyes, nose, mouth and ears can be seen, and fingers and toes start to appear.

As the unborn baby grows, so does the uterus. A fluid-filled double membrane surrounds the baby, and during pregnancy it floats freely in the amniotic fluid. The baby constantly swallows this fluid and excretes it in the urine, so much information about the health of the baby can be obtained during a test called Amniocentesis. The membrane normally breaks and releases the amniotic fluid before the baby is born.

The length of a normal pregnancy varies between about 37 and 42 weeks, although the delivery (term) date is calculated at 40 weeks from the first day of the last period. Only around five per cent of babies are born on their due date. Babies born before 37 weeks are considered premature (or pre-term).

Definition

Weeks 0 to 13 are known as the first trimester of pregnancy. The baby's development is greatest during this stage, and by the end of week 13 it will be fully-formed. Some of the common discomforts of pregnancy such as nausea, fatigue, and breast tenderness will be most pronounced during these early weeks.

Weeks 14 to 26 make up the second trimester. During this time, the baby continues to develop and grow, and the mother may start to gain significant amounts of weight as extra fat is laid down as energy reserves. This is also the time when the baby's movements in the uterus can be felt, and s/he may begin to develop patterns of activity.

The third trimester runs from week 27 to the birth of the baby. It starts to lay down its own fat stores, going through rapid growth phases in preparation for birth. The lungs are also maturing, and senses such as hearing, taste and sight are developing. The woman may find it more difficult to get comfortable at night, with backache, frequent urination and practice contractions known as Braxton Hicks a more regular feature.

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Some signs and symptoms to look for if you believe you might be pregnant include:·

missed menstrual period,
nausea, with or without vomiting,
tiredness,
breast changes and breast tenderness, and
frequent urination.
Feelings of sickness (nausea) affect the majority of women during pregnancy, particularly during the first three to four months. Tiredness may be more pronounced during the first and third trimesters.

The diagnosis of pregnancy is mainly determined by testing for the pregnancy hormone human chorionic gonadotropin (HCG). HCG can be detected in the woman's blood and urine even before the first missed period. It is this hormone that is measured by home pregnancy tests. A high HCG level may indicate a multiple pregnancy (e.g. the presence of twins or triplets), although the most reliable test is an abdominal or transvaginal scan.

Abdominal or transvaginal scans may be used to confirm pregnancy, how many embryos are present, and whether the embryo is located in the uterus (and not in the fallopian tube in the case of ectopic pregnancy).

Folic acid is highly recommended during the first twelve weeks of pregnancy (and before conception where possible). Iron supplements may be recommended by the midwife or GP if pregnancy-related anaemia has been diagnosed.

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It is common for pregnant women to experience several of the following conditions:·

anaemia,
constipation,
haemorrhoids,
heartburn,
hypertension (high blood pressure,
hypotension (low blood pressure),
gum disease (gingivitis),
genital infections such as thrush (candida) and trichomoniasis,
mood changes,
nausea and vomiting, and
urinary tract infections.
It is very important to attend all antenatal appointments with your midwife, GP or consultant. Conditions such as pre-eclampsia can be detected only through regular antenatal checks. Symptoms include sudden swelling of feet and ankles, rapid weight gain, vision problems (blurring or flashing lights in front of the eyes), abdominal pain and headaches.

Nausea and vomiting in pregnancy is usually called morning sickness because the morning is when most pregnant women experience it, but in reality it happens any time during the day or night. Whilst some few women never get it at any time in the pregnancy, most experience at least some mild morning sickness. In a few women it can be severe - this condition is called hyperemesis gravidarium and may require treatment in hospital.

Bleeding, unusual vaginal discharge or loss of fluid from the vagina, lower back pain and/or abdominal pain, and (from the second trimester onwards) changes in foetal movement should also be acted upon quickly, so that the health of the baby can be monitored.

Approximately one pregnancy in four ends in miscarriage, most of these occurring in the first 12 weeks of pregnancy. For many women, the first indication of miscarriage is vaginal bleeding or discharge, sometimes accompanied by abdominal pain or backache- rather like period pains. Some women may notice that pregnancy symptoms such as nausea or breast tenderness disappear. Vaginal bleeding in early pregnancy is called 'threatened miscarriage', but does not necessarily develop into a miscarriage. Many women will go on to have a normal pregnancy.

Ectopic pregnancy occurs when the fertilized egg (ovum) becomes implanted in an abnormal site inside the body instead of in the womb lining. It is a potentially dangerous condition, as it can cause severe internal bleeding. Early diagnosis and surgical treatment are essential.

Pre-eclampsia is a condition which occurs only during pregnancy, or immediately after delivery of the baby. Women develop high blood pressure together with protein in the urine and fluid retention (oedema). Pre-eclampsia develops in about 1 in 10 pregnancies, usually after the sixth month of pregnancy. Most cases are mild, develop towards the end of the pregnancy, and are easily treated. However, in a severe form it can be life-threatening for both mother and baby.

Placenta praevia occurs when the placenta covers part or all of the cervix. It may cause bleeding in the pregnancy, and if the placenta does not move up as the pregnancy progresses, a caesarean birth will be necessary. In most women, the placenta moves out of the way before birth, but additional ultrasound scans may be required to monitor the situation.

Other tests during pregnancy can detect any chromosomal conditions, such as Down's Syndrome. This occurs when one of the 23 pairs of chromosomes (inherited from each parent) has an extra chromosome attached, resulting in learning disabilities and sometimes health problems. Women at higher risk of carrying a baby with such conditions may opt for testing procedures like amniocentesis or chorionic villus sampling (CVS).

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