Everyone knows that the uterus grows during pregnancy but what most women do not know is the size of their uterus before they show any obvious signs of early pregnancy. They also wish to know whether the size of their uterus is normal for the duration of their pregnancy. One of the first things to realize is that the clinical diagnosis of very early pregnancy is almost impossible by ordinary routine examination and it is for this reason that pregnancy tests were designed and are performed. The earliest detectable changes in the uterus do not occur until approximately 6 weeks after the first day of the last menstrual period when the uterus becomes softer as well as larger. Its very softness makes it so difficult to palpate that it is frequently impossible to determine its exact size; indeed the uterus may become so soft at about the 8th or 10th week of pregnancy that it may be extremely difficult to feel it at all.
Before the onset of pregnancy the uterus varies in size from person to person, but on average measures approximately 7 cm. in length, 5 cm. in width and over 2.5 cm. in thickness, while at full term it can measure as much as 38 cm. in length, 25.5 cm. in width and 20 cm. from front to back. The weight of the uterus itself increases throughout pregnancy approximately twenty times from a pre-pregnant weight of 40 gm. to almost 800 gm. immediately after delivery.
The enlargement of the wall of the uterus during pregnancy is entirely due to the enlargement of the muscle. This is accomplished by an increase in size of the existing muscle fibres not the creation of new muscle fibres, so that despite the enormous increase in the size during pregnancy the actual thickness of the wall of the uterus at full term is almost exactly the same as it was before pregnancy began.
It is very difficult to appreciate absolute size when it is given as a simple measure. To compare the sizes of the normal uterus in the early stages of pregnancy we can consider that if it begins as a tangerine orange, then at 6 weeks it will be the size of a normal apple. At 8 weeks it will be the size of an average orange and at 10 weeks the size of a Jaffa orange. At 12 weeks the uterus will be as large as a grapefruit and at 14 weeks approximately the size of a small melon.
The uterus is normally mobile and is free to move within the pelvis not only when the bowel and bladder fill and empty, but also during intercourse or even when walking. In the 12th week of pregnancy the uterus becomes too large to remain hidden in the pelvis. It is at this stage that it can be felt in the lower abdomen rising out of the pelvis, or even earlier if the bladder or rectum are unduly full.
From the 12th week of pregnancy the uterus enlarges at a regular rate to reach the umbilicus at about the 22nd week. At about the 16th week it is half-way between the symphysis pubis and the umbilicus. At the 30th week the uterus will be half-way from the umbilicus to the xiphisternum, which is the small piece of cartilage attached to the lower end of the breast-bone, to which the ribs are joined in the front of the chest. At 36 weeks the uterus reaches the xiphisternum in the mid-line.
In a woman who is having her first baby, a phenomenon known as ‘lightening’ may occur at or about the 36th week of pregnancy. Lightening is caused when the baby’s head descends into the cavity of the pelvis and this is accompanied by lowering or dropping in the level of the top of the uterus—hence the term or phrase ‘lightening’. The baby continues to grow and the uterus enlarges further so that by the 40th week of pregnancy the top or fundus of the Uterus will have again returned to the xiphisternum even while the baby’s head is engaged in the pelvis. In the multiparous woman (that is a woman who is having a second or subsequent baby), the fundus of the uterus reaches the xiphisternum at the 36th week of pregnancy and remains there until the head of the baby engages in the pelvis, usually at term or the onset of labour.
The structure of the uterus changes during pregnancy. The changes are at first very slow and poorly defined but later they are more rapid and easily discernible. The body of the uterus becomes very soft and rounded in early pregnancy but as it enlarges and moves up into the abdomen it resumes its pear-like shape. Most of the new muscle fibres that form in the wall of the uterus during pregnancy are present in the upper part, or body of the uterus.
At about the 30th week of pregnancy, the repeated contractions of the uterus, most of which occur in the upper part, gradually lead to the formation of the lower uterine segment. This is the lower part of the body of the uterus which gets thinner during the last 10 weeks of pregnancy and gradually enlarges in order to accommodate the baby’s head and in order to facilitate the subsequent mechanism of labour, especially the dilatation of the cervix.
The cervix, which before pregnancy is firm and hard, very rapidly becomes soft as well as larger but does so very slowly throughout pregnancy. The canal of the cervix remains filled by a tenacious plug of thick mucous material which occludes it and prevents any infection ascending from the vagina into the uterus.
The Blood Supply
The blood supply to the uterus, as indeed to all the pelvic organs, increases very rapidly and dramatically during early pregnancy. Some of the earliest physical signs upon which pregnancy can be diagnosed are in fact the result of the rapid increase in blood supply. The cervix not only starts to become soft but first of all it assumes a blue or purple colour. In the non-pregnant woman the arteries that supply the uterus cannot normally be felt when vaginal examination is performed, but their pulsation can be easily recognized as early as the 6th week of pregnancy. The blood supply to the enlarging uterus increases rapidly as pregnancy advances, so that at full term it is approximately 25 per cent of the total body circulation.
Contractions of the uterus occur throughout life but become especially well marked and important during pregnancy,when they are known as Braxton Hicks’ contractions. They are extremely important both for the growth of the uterus and for the satisfactory circulation of blood through the uterine vessels. A Braxton Hicks’ contraction occurs approximately every 20 minutes throughout pregnancy and is usually felt as a painless but nevertheless quite definite hardening of the wall of the uterus itself which lasts for about 20 seconds.
The Fallopian Tubes
The Fallopian tubes change very little during pregnancy, although they do increase slightly in size, and their blood supply, like the blood supply to all the pelvic organs, is also increased. The vital role of the Fallopian tubes during the first seven days of pregnancy in transporting the newly fertilized ovum to the uterus is described. Having undertaken this vital function they take no further part in the pregnancy.
The ovaries are responsible for the production of the ova and once an ovum has been fertilized the Fallopian tubes transport it to the cavity of the uterus.
Following ovulation the corpus luteum develops in the ovary and is responsible for the production of progesterone. The corpus luteum continues to enlarge for the first 12 weeks of pregnancy and if it is damaged or removed during this time the level of progesterone in the body will fall suddenly resulting in the disintegration of the decidua lining the pregnant uterus. This will result in both death of the ovum and shedding of the lining of the uterus’ together with the ovum.
As soon as the placenta is properly formed at about the 12th or 14th week of pregnancy, it begins to produce hormones of which progesterone is the first. By the end of the 14th week it is producing enough progesterone to make the pregnancy self-supporting, so removal or destruction of the corpus luteum will not usually affect the pregnancy. The corpus luteum gradually shrinks after the end of the 14th week and although it may be recognized even up to the end of pregnancy it ceases to exert any significant influence on the pregnancy itself.
The corpus luteum may occasionally cause pain or tenderness in the side of the pelvis during early pregnancy. The exact reason for this is not known and no treatment is required because the pain always subsides spontaneously.
The ovaries themselves enlarge during pregnancy and may occasionally develop small cysts. These are normal changes and a few months after the end of pregnancy the cysts disappear and both the ovaries return to their normal size and shape.
Some of the earliest noticeable changes in pregnancy occur in the vagina. The blood supply is increased, a certain amount of congestion occurs and, as the circulation slows down, the colour changes from the normal pale pink to a darker, suffused pink or even pale blue or lilac. This becomes more marked as pregnancy advances, so that at term both the vagina and the cervix may be purple.
Vaginal secretions begin to increase early in pregnancy causing a certain amount of mucoid discharge. The quantity of discharge varies from woman to woman throughout pregnancy, but a certain amount is considered normal. If it becomes offensive, profuse, causes any pain, soreness or irritation, it has probably become infectcd and should be mentioned at the next antenatal clinic, so that appropriate treatment may be given.
An increase in the rate or frequency of micturition is often one of the earliest symptoms of pregnancy and may continue until delivery. This is because the uterus is still within the pelvis for the first three months and presses on the bladder. So long as there is no pain or discomfort when passing water frequency should be accepted as normal in early pregnancy.
The amount of blood normally present in a woman of average height and weight is approximately 5 litres. Very extensive changes take place in the blood during pregnancy caused initially by the rise in hormone levels Which results in a gradual increase of the amount of blood circulating throughout the body. After mid-pregnancy the uterus needs about 25 per cent of the circulating blood. The breasts and other organs that increase in size also require an increased blood supply. These demands can be met either by depriving other organs of their normal blood supply or by increasing the total amount of blood available within the body It is the latter alternative that the body adopts and from the 10th to the 34th week of pregnancy the amount of blood circulating throughout the body gradually increases by as much as 5 2 per cent or even 40 per cent. The circulating volume thereafter remains relatively constant until very close to term, when it may fall slightly. As soon as the hormone levels fall after delivery the blood volume rapidly returns to normal.
The rapid increase in the amount of blood circulating in the body during pregnancy is mainly accomplished by an increase in the serum or plasma. Unless this increase is also accompanied by a similar rise in red cells, these will be diluted in the blood resulting in anaemia.
The pregnant woman needs a great deal of iron and nutrition. The baby takes iron from his mother to form his own blood and, in addition, her own bone marrow needs it to manufacture a larger number of red cells for the increasing volume of blood that her body demands. It is obvious, therefore, that anaemia can very easily develop and one of the major principles of antenatal care is its prevention by giving the mother plenty of iron and vitamins and frequently checking her blood. If all pregnant women attended the antenatal clinic early in pregnancy and took their full complement of iron and vitamins, anaemia during pregnancy would be comparatively rare.
The Blood Pressure
Important changes may occur in the blood pressure very early during pregnancy. One of the major actions of the hormone progesterone is to cause relaxation of the involuntary muscle of the blood vessels as well as of the uterus, the bladder and intestine. Relaxation of the muscular wall of the blood vessels causes some delay in the circulation through some of the tissues (it is this slowing down in circulation of blood supply to the vagina that is responsible for its change in colour in early pregnancy). The slowing in the circulation causes a fall in blood pressure which is very common in early pregnancy. This may lead to a sensation of light-headedness or even fainting, especially after prolonged standing in one position (as in a bus queue). You should be aware of this tendency to faint in early pregnancy and therefore avoid standing in one position. If this is unavoidable, you should move your weight from one foot to the other to help the circulation through the legs. If you feel light-headed or feel as though you are going to faint, an actual fainting attack can be averted by taking a few rapid very deep breaths.
The fall in blood pressure in early pregnancy is usually only small in amount and is perfectly normal. It is frequendy associated with a certain amount of tiredness or lack of energy and lassitude, and this may be interpreted as one of nature’s ways of ensuring that you rest and do not indulge in too much exercise during this vital stage of pregnancy.
After about the 14th week of pregnancy the tendency to light-headedness or fainting disappears because the blood pressure rapidly returns to normal as the body increases the amount of blood within its circulation. It will remain at or about the same level until the onset of labour. Your blood pressure will be checked at every antenatal clinic because any abnormal rise may be one of the first signs of pre-eclampsia and the associated complications can be prevented if diagnosed early.
The work of the heart is considerably increased during pregnancy. The increase in work load is small at the onset of pregnancy but it may increase by as much as 40 per cent at about the 28th week. It is small wonder, therefore, that many women feel tired and lethargic towards the end of pregnancy and this is one reason why there should not be too large a weight gain. Cosmetic reasons apart, the more weight gained, the more work the heart has to do.
The heart itself behaves in quite an astonishing way during pregnancy. If you feel your own pulse when you are 36, 38 or even 40 weeks pregnant, it will feel exactly the same as it did before you became pregnant. While resting, the rate is about 80 beats per minute and you will detect little change from the 70 beats per minute of the normal non-pregnant pulse. The heart enlarges during pregnancy and is so adaptable that it can increase its amount of work by at least 40 per cent with only a slight increase in rate and no change in rhythm The increase in heart rate of 10 beats per minute represents 14,000 beats per day! It manages to accomplish all this even though it is gradually being pushed further up into the chest by the enlarging uterus. The increased load on the heart during pregnancy is another vital reason why anaemia, as well as excessive weight gain, should be avoided.
The heart returns to its normal shape, size and position within three or four days of confinement.
The lungs change very little during pregnancy but they do have to work at a considerable disadvantage during the last four months. The enlarging uterus pushes up against the diaphragm and gradually squeezes them into a smaller and smaller area within the chest. The reaction of the chest is to spread the ribs out sideways in order to provide the lungs with more room.
A certain amount of automatic compensation occurs within the lungs so that even at the 40th week of pregnancy you will be able to breathe quite easily and normally. You will notice, however, that you do occasionally take big, deep or sighing breaths. Sometimes normal non-pregnant people do this, but you may notice yourself doing it more frequently and this is absolutely normal. If you have a twin pregnancy, or if for some other reason your uterus is unduly large, then you may find that breathing can become difficult towards the end of pregnancy. This may be especially noticeable when you sit down, and the lower you sit the more noticeable will it be. It is for this reason that you will be more comfortable in a comparatively high chair which also has a relatively straight back, for the further down or the further forward you slump, the more difficult does it become for your chest to move and your lungs to expand satisfactorily. You may also need extra pillows in bed to ensure maximum comfort at night.
The lungs return to normal almost immediately after delivery.
The Nervous System
No fundamental changes occur in the central nervous sytem during pregnancy although certain emotional changes, and even variations in personality, are evident very soon after conception and continue to a greater or lesser degree until about six months after delivery.
Several physical changes in the body do, however, have some effect on the nervous system, causing tiredness, lassitude or occasional feelings of faintness (sometimes actual fainting) during the first 14 weeks of pregnancy.
Headaches, not generally considered a feature of pregnancy, are suffered more frequently by some women when they are pregnant. The reason for this is not known.
Backache is usually the result of bad posture or weight gain in association with the softening of the ligaments in the spine. It has nothing to do with the central nervous system although patients who have previously suffered from a slipped disc should be especially careful during pregnancy.
As pregnancy advances into its last 8 or 10 weeks, the baby’s head may bounce on nerves in the brim of the pelvis resulting in shooting pains down either the front or the back of the legs. These are usually transient, although occasionally causing considerable discomfort, and nearly always disappear when the baby moves its head, and certainly go after delivery.
The main changes that occur in the skeleton during pregnancy take place in the pelvis. The pelvic bones themselves do not alter, but the ligaments, especially in the region of the sacro-iliac joints at the back and the symphysis pubis in front, soften and become more elastic. The bones can therefore move quite appreciably during pregnancy to increase the capacity of the pelvis, and especially in labour to facilitate the passage of the baby.
Most of the ligaments in the body soften during pregnancy and are more liable to be stretched. It is most important that the ligaments in the back and in the feet should not be overstretched. Correct posture goes a long way towards preventing this, and shoes giving proper support to the feet should be worn throughout pregnancy.
During the last two months of pregnancy the ribs may be increasingly pushed upwards and outwards by the pressure of the uterus. This is more often on the right side, and may lead to pain and discomfort known as costal margin pain which disappears after delivery.
An increase in pigmentation of the skin occurs during pregnancy . It is generally accepted that this is greater in women with dark hair than in women with fair hair, and red-heads have very little or no extra skin pigmentation during pregnancy. As well as the specific pigmentation which may occur on the breasts and on the abdomen, moles and freckles tend to both darken and increase in size. Excess or extra hair does not form during pregnancy but it often happens that previously very fair and unnoticed hair on arms and legs, and occasionally even on the abdomen and back, becomes darker and is then noticed for the first time. The colour of the hair will return to normal after delivery although some women do complain that the hair on so-called ‘hairy warts’ does not always return to its former colour.
Generalized irritation of the skin frequently associated with dryness is not uncommon during pregnancy. The cause of this is unknown but it may be due to a shortage of one of the members of the vitamin B group, and so it is wise to make sure that an adequate amount of vitamin B is taken. Otherwise there is very little that can be done for this condition besides treating the underlying dryness, which may be causing the irritation, with oil or creams.
Local areas of irritation can result from any skin disease or, for instance, from such simple things as varicose veins which can occasionally cause a most annoying itching and irritation of the overlying skin. Vulval irritation may be caused by vaginal discharge and, if so, the discharge itself should be treated. Irritation around the anus may be the result of piles or of sweating and overweight. Cleanliness and hygiene will do much to alleviate these complaints.
Beneath the surface of the skin there are elastic fibres which, under normal circumstances, allow the skin to stretch and contract to maintain its normal flexibility and pliability. If these clastic fibres are overstretched so that they rupture, the skin over them will be unduly stretched and a ‘stretch mark’ will appear. Stretch marks appear with alarming suddenness (literally overnight) and they are brightish red in colour. Once they have begun they may extend or adjacent marks may appear.
During pregnancy stretch marks may occur on the abdomen. They may also appear on the breasts in early pregnancy, when they are usually associated with sudden breast enlargement resulting from the rapid rise in hormone levels. Their appearance is not associated with any generalized increase in weight, although overweight women are more likely to develop them. The red discoloration continues throughout pregnancy but eventually fades leaving silvery, rather thin scars which will never entirely disappear.
Stretch marks may occur at puberty on the buttocks and also on the breasts, especially if a girl is overweight.
The skin certainly seems to change during pregnancy but the reason for these alterations is not known. Women who have a greasy skin usually find it becomes more greasy and those with a normally dry skin find it becomes drier. Little can be done for those whose skin becomes more greasy other than ensuring that too much weight is not gained and keeping skin creases and folds scrupulously clean.
Increased dryness of the skin will do no harm although it may cause a mild itching or irritation. Dry skin, of course, tends to wrinkle and therefore meticulous care should be taken of the skin during the entire pregnancy. This is best accomplished by rubbing a small amount of oil or baby lotion gently over the affected parts once or twice a day. A little bath oil or baby oil in the bath gives the whole body a thin, but nevertheless adequate, coating of oil which will help prevent dryness and alleviate irritation.
Scrubbing, hard water, harsh soaps, strong detergents and face powder all tend to dry the skin and should be used with caution on skin with this tendency. Particular attention must be paid to the skin on the face, by using satisfactory make-up and applying a liberal amount of a good moisturizing cream at night.
Changes in the breasts are probably the earliest symptoms of pregnancy. Most women are aware of some fullness in the breasts immediately preceding the menstrual period which normally disappears as soon as the period commences. With the onset of pregnancy, however, it continues and gradually becomes more obvious. By the 6th week of pregnancy, that is, two weeks after the first missed period, the breasts will show very definite enlargement. They will be firm and there will be a certain amount of tenderness throughout the whole of the breast tissue. There is at this time an increase in both the size and the number of the veins on the surface of the breasts and these are easily visible. Even before these obvious changes, sensations of tingling may occur, and some women complain of an increase in the sensitivity of not only the nipple but the whole breast as well. Occasionally, there may be actual pain in the breast itself, caused by the rapid enlargement in the breast tissue.
Millions of years ago the breast was developed from an ordinary gland in the skin and as the human race has evolved the breast has differentiated into an organ capable of producing enough milk to feed a baby. The nipple itself is surrounded by an area of pink, rather tender and delicate skin which is known as the areola. Six to fifteen smaller vestigial glands are situated in the areola and are not normally visible or palpable in the non-pregnant woman. They do, however, respond to pregnancy in exactly the same way as the breast itself. At about the 6th week they become obvious as small, raised, pink nodules approximately 3 mm. in diameter, known as Montgomery’s tubercles. They are not usually tender but may occasionally become so, and their presence is one of the most reliable early signs of a first pregnancy. They are less reliable as a diagnostic sign in subsequent pregnancies because they do not shrink completely after delivery.