The Third Trimester of Pregnancy


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The final stage of pregnancy is a roughly 3-month period called the third trimester. During this time the foetus grows far more quickly in terms of its size and weight, and as such the third trimester is the most visually dramatic stage of pregnancy, wherein the ‘baby bump’ is most visible. The third trimester is also the point at which childbirth is often at the forefront of people’s minds.

What happens to my body during the third trimester?

The third trimester will involve rapid weight gain as your unborn foetus’ puts on as much as 28g every day in what is undoubtedly the most rapid period of growth for both foetus and mother. There is a distinct difference in the shape of your belly during the third trimester, where the foetus moves to face downwards in preparation for birth. Generally the pregnant belly is higher up in the second trimester, and drops significantly in the third trimester as a result of foetal movement.

Generally speaking you will put on as much as 4 pounds of weight during the 7th month, another 5 pounds during the 8th, and as much as 9 pounds during the final month of a pregnancy. During this time the added weight, as well as the fact that a rapidly growing foetus is using up a lot of the food you eat, will probably make you feel more tired. You can also experience some shortness of breath, which is in fact not only to the increased weight but also because of the effects the growing foetus has on your respiratory tract. The foetus is housed inside the womb, also known as the uterus, a structure which expands rapidly during the pregnancy and pushes up on the diaphragm by as much as 4cm, enough to considerably impact your lung capacity (the volume of air your lungs can take in).

Fortunately this won’t have any lasting or dangerous effects for you or your baby. All it really means is that you can experience some discomfort during this stage of the pregnancy. Your body actually compensates for the reduced lung capacity, as progesterone, a female hormone which is present in large quantities during a pregnancy, actually affects how deeply you breathe in during a pregnancy.

There are some steps you can take towards minimising the shortness of breath which is a natural part of the third trimester. These include, for example, improving your posture to ensure that your lung capacity is as large as possible. What this means is ensuring that your back is straight while your shoulders are relaxed rather than hunched up. You might be pleasantly surprised at what a difference this can make.

Remember that while some mild shortness of breath is natural, any extreme and unpleasant breathing difficulty is not, and you should consult your doctor as soon as possible if you experience anything of the sort. Chest pain and unusually shallow breathing and pulse rate are common signs of a serious problem like a blood clot in the lungs.

One of the adverse effects of the many hormones that circulate in abundance during a pregnancy is an unwanted affect on the connective tissue found within joints. This results in the hip pain that affects so many pregnant women, which is caused by a loosening of parts of the hip joint. Typically speaking hip pain like this will usually affect one side rather than both, and the fact that the foetus is putting on weight very quickly contributes to the discomfort.

Many pregnant women experience a particular set of sensations called sciatica. Sciatica is essentially any kind of numbness, pins and needles, tingling, or even pain that extends from the lower back and runs down towards your feet. This is called sciatica because the sensations affect the sciatic nerves. Sciatica is usually a normal part of pregnancy, but you should keep your doctor informed just so they can make sure there is nothing else amiss.

Sometimes a sharp vaginal pain is experienced during the third trimester, and this is a consequence of one of the body’s preparation for childbirth, the dilation of the cervix. Any unexpected vaginal pain and bleeding, or in fact any of these affecting the lower part of your belly, should always be reported to your doctor as soon as possible.

Varicose veins are often a result of third trimester pregnancy, and while unwanted they are not anything to worry about, and a natural consequence of the pregnancy. These occur as a result of the additional stress a rapidly growing foetus places on your circulatory system. Itchiness in the abdominal region is also a common feature of the third trimester.

Most mothers to be will have some trouble sleeping in the final weeks of a pregnancy. This can be the consequence of any of the physical changes discussed above, as well as a result of nerves about the upcoming delivery of your child. There are steps you can take to make yourself more comfortable, including, for example, sleeping with your legs bent and on your side to relieve some pressure from your lower back. Similarly using a pillow to support your belly as it gets larger is a good way to get comfortable.

What happens to the foetus during the third trimester?

The third trimester is largely a period of growth rather than development for the foetus. By this point, the major organ systems have developed and many have started functioning, all that’s left is for these structures to finish growing so that they can function completely independently. Foetal movement is dramatically increased during the third trimester as well.

Other points about the third trimester

One of the most important points to bear in mind about the third trimester is that at this point an unborn foetus is using up a lot of the mother’s reserves of nutrition to grow. Therefore adequate nutrition and regular rest are two very important practices that can ensure at least some level of comfort for pregnant women. Heavy lifting and exertion should be avoided to ensure the health and safety of both mother and child.


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