4 weeks pregnant: Changes for mum

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There are many changes going on inside your body that you’re not aware of, and some very subtle changes to the appearance of your body which may give you the first signs that you’re pregnant.

Increased blood volume

Immediately after conception, the amount of blood your body produces increases. This is to ensure that there is sufficient blood to carry oxygen and nutrients to your developing baby. Blood production continues to increase throughout your pregnancy so that by the end of pregnancy you will have an additional 30-50% more blood than at the beginning of your pregnancy. The changes in blood volume occur most rapidly in this first trimester of pregnancy.

Increased heart rate which may cause fatigue

Your heart begins to beat a little harder and faster to pump the additional blood through your body, resulting in pulse rate increases of up to 15 beats per minute. The most obvious effect of increased blood volume and heart rate is fatigue. If you find yourself feeling exhausted right after dinner or needing an afternoon nap, it’s probably because of all the extra work your heart is doing to pump that extra blood through your body and to your new bub.

Breast changes

The way your breasts feel may also start to change this week. Typical feelings include tingling, tenderness or soreness. Your breasts may also feel fuller or heavier than usual. The areolas (the darker pigmented skin around your nipples) may get bigger or darker because of the additional blood that is circulating in your body. Tiny bumps may also appear on the areolas, known as Montgomery’s tubercules. These little bumps secrete substances which lubricate the nipples and ward off infection during breastfeeding. You won’t begin breastfeeding for many months to come, but your super-organised body is already preparing itself for breastfeeding.

Cervical changes

The cervix, the entrance to the womb which connects it to the vaginal tract, also undergoes changes this week. It softens and changes colour. You are not able to see these changes, but your doctor may look for changes in your cervix to confirm your pregnancy at this very early stage.

Development of the placenta and changes in the circulatory system of the uterus

The tiny collection of cells growing inside you has already divided into two groups of cells, those that will form the placenta (an organ which grows only during pregnancy to nourish your baby), and those that will eventually grow into you baby.

The group of cells which will form the placenta become active this week and begin releasing a hormone called human chorionic gonadotropin (hCG for short). This is the hormone that pregnancy tests search for to determine whether or not you’re pregnant. hCG is only produced by the placental cells and not by other cells in your body. So if hCG is in your urine or blood, it means there’s a placenta in your womb, and by default, you’re pregnant! You may not look pregnant yet, and still haven’t missed your period, but in some cases, by the end of the second week of pregnancy a simple test can already tell you, based on whether or not hCG is detected, if you are pregnant. hCG is detectable 6-12 days after fertilisation (day 21-27 after your last menstrual bleeding), so it’s better to wait until at least the end of the fourth week of pregnancy to take a pregnancy test.

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hCG is produced to stimulate a structure called the corpus luteum to produce the large amounts of the hormone progesterone, and to a lesser degree oestrogen. It takes over from follicle stimulating hormone and luteinising hormone which have regulated your body’s oestrogen and progesterone production in the first three weeks of pregnancy.

The corpus luteum (literally translated, this means yellow body) forms inside the ovaries from the remains of the dominant follicle, that is the follicle in which the egg, released when you ovulated about the end of the second week of pregnancy, matured. The large quantities of hormones produced by the corpus luteum are needed to support your pregnancy, prevent menstruation, and ensure your baby begins its nine months of growth. If fertilisation does not occur and enable the development of placental cells and hCG production, the corpus luteum degenerates. In the absence of large amounts of oestrogen and progesterone produced by the corpus luteum, the lining of your uterus which nourishes the embryo will break away, resulting in menstrual bleeding.

Emotional changes

Don’t be surprised if you’re emotional this week. New and sometimes unsettling emotions occur in this early period of pregnancy. Whether or not your pregnancy was planned, you may have mixed emotions. Even if falling pregnant is the best thing that’s ever happened to you, you’ll probably have some concerns, for example about the health of your growing baby or about the financial demands which will be placed on you and your partner when the baby is born. It’s perfectly natural to have some doubts.

Mood swings are also a fairly common symptom in the early weeks after fertilisation. If you find yourself on top of the world one minute and a bit down the next, it’s probably frustrating, but it’s perfectly normal. Emotions change rapidly, sometime several times a day. This may be a result of fatigue, related to the physical changes occurring in your body, or because of the hormonal changes which are taking place.

Your moods will also be influenced by the people around you and particularly your partner and family. If your partner has mixed feelings about your pregnancy, this is likely to influence your moods. It’s important to take time out to talk about any concerns either of you have, so these worries or doubts don’t cause emotional distress. It’s perfectly normal for both you and your partner to have concerns, and getting them out in the open is important. Talk to your partner about how you’re feeling so that miscommunication doesn’t lead to hurt feelings. For example if you’re too tired to have sex when your partner really wants to, explain how you’re feeling so they don’t feel rejected.


More information on the 4th week of pregnancy

For more information on the fourth week of pregnancy, see 4 weeks pregnant.
For more information on the changes happening to growing babies in the fourth week of pregnancy, see Changes for baby this week.
For more information on doctor appointments and other lifestyle changes to adopt, see Pregnancy health and lifestyle information this week.
For more information on the key points of fourth week of pregnancy, see Key points this week.
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Date Created: August 23, 2012 Date Modified: August 29, 2012