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Week 3 of Your Pregnancy

The third week of gestation corresponds to the third week after the date of the last menstrual period (LMP). Normally, the woman does not yet know that she is pregnant, and pregnancy tests can still give rise to false negatives.

Actually, this third week of pregnancy would be the first week of embryonic development. However, all professionals in the field take as a reference the beginning of the menstrual cycle to start counting the weeks of pregnancy in a 40-week gestation. This is known as gestational age. Therefore, during this third week of pregnancy, the events that take place are fertilization and the beginning of embryo development.

Here you can find all of our 1st trimester articles:

What happens in the third week of pregnancy?

At the end of the second week or beginning of the third week of pregnancy, ovulation occurs. These are the woman’s fertile days and, therefore, the couple must have unprotected intercourse for conception to occur.

After intercourse, the ejaculated sperm begin their journey through the female reproductive tract: they ascend the cervix, pass through the uterus and reach the fallopian tubes. It is here that the encounter with the egg and fertilization by a single sperm takes place.

Once the egg and sperm have united, their nuclei fuse, containing the genetic material of both parents. At 16-20 hours post-fertilization, the embryo consists of a single cell and is called a zygote. From here, the zygote begins its descent down the fallopian tube towards the uterus. At the end of the third week of pregnancy, the embryo arrives in the uterus, when it is at the blastocyst stage.

Journey of the embryo down the tube

As we have said, after fertilization, embryonic development begins and the embryo descends through the fallopian tube until it reaches the uterus.

This journey is made possible by small contractions of the tubal muscles. In addition, its inner surface is covered with millions of cilia, small hairs that move in the same direction, which produces a dragging of the embryo through this duct.

It should be noted that it is at this moment when there is a risk of ectopic pregnancy, i.e., the embryo is nested in the fallopian tube and an extrauterine pregnancy occurs, which is not viable.

The hormone progesterone secreted by the ovary after ovulation also plays an important role during this process. Progesterone, also known as the pregnancy hormone, allows the relaxation of the sphincter that exists between the fallopian tube and the uterus, thus allowing the passage of the embryo. In addition, progesterone also prepares the uterus for embryo implantation by increasing endometrial receptivity.

Third Week of Pregnancy

3rd week: changes in the mother

In the third week of pregnancy, when conception has already taken place, the woman does not undergo major changes in her body and does not feel anything yet. In fact, most of the time she does not even suspect that she is pregnant.

Only patients undergoing fertility treatments such as artificial insemination (AI) or in vitro fertilization (IVF) notice some symptoms during the period known as beta-pregnancy.

Despite this, hormonal alterations during this third week of gestation may result in symptoms such as the following:

  • Breast tenderness
  • Increased perception of odors
  • Taste alterations and increased salivation
  • Mood swings and irritability
  • Tiredness
  • Headache
  • Increased urge to urinate
  • Thick white discharge

Normally, this third week of pregnancy passes without any noticeable symptoms for the woman. In fact, there is still a week before menstruation and women do not usually take a pregnancy test before the delay in menstruation.

Is it possible to do a pregnancy test?

If a pregnancy test is taken during week three of pregnancy, it would most likely be negative because the beta-hCG hormone has not yet begun to be secreted. Assisted reproduction patients also run the risk of getting a false positive pregnancy test during this week, as the hormone medication administered during treatment can lead to an erroneous result.

The beta-hCG hormone corresponds to the beta fraction of the human chorionic gonadotropin hormone, which is produced by the embryo once implantation has taken place and is detected by a pregnancy test.

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Care during the third week

A woman’s habits and behavior can influence the baby’s development from the beginning of pregnancy. It is therefore advisable to follow a healthy lifestyle, especially if the pregnancy is expected.

Here are some tips of interest during the first weeks of pregnancy:


Folic acid is one of the most important vitamin components for pregnant women, as it helps prevent neural tube defects in the fetus, which could lead to diseases such as spina bifida and anencephaly. Folic acid is found in green leafy vegetables, such as spinach or chard, and legumes.

During the first few weeks of pregnancy, gynecologists may recommend starting to take iron-rich foods or vitamin supplements. This mineral is necessary for hemoglobin formation and to prevent anemia. Red meat in moderation is an excellent source of iron. As for foods that help the absorption of iron, we find tangerines, strawberries or tomatoes rich in vitamin C.

Another very important mineral for pregnant women is calcium, as it helps prevent hypertension or preeclampsia. Calcium intake also contributes to the optimal development of the baby’s nervous and muscular system. Therefore, it is advisable to follow a diet rich in calcium from the beginning of pregnancy.

As for the foods that should be avoided from the moment a woman knows she is expecting a baby, they are the following: raw fish or fish rich in mercury, raw meat, coffee, undercooked eggs, unpasteurized cheese, etc. All these are preventive measures to avoid toxoplasmosis and listeriosis. It is also necessary to wash fruits and vegetables properly before eating them.


In addition to taking care of your diet, it is also important to keep your body healthy through exercise. However, high-intensity sports should begin to be replaced by gentler ones such as Pilates, yoga, swimming, etc.

It is also important for women to get adequate rest and sleep. To this end, going for a walk every day can help to relax the body and maintain good sleep habits. It is not advisable to give up physical activity completely, unless it is a high-risk pregnancy and the doctor recommends it.

FAQ - Third week of Pregnancy

✅ What month corresponds to the third week of pregnancy?

The third week of gestation corresponds to the first month of pregnancy, but the woman has not yet had the menstrual delay and does not know she is pregnant.

On the other hand, the embryo has only one week of embryonic development. It has just been conceived and consists of only a few cells. It is not yet called a fetus because it has not yet implanted in the uterus. Nor is it possible to visualize it with an ultrasound because its size is minuscule and the gestational sac has not yet formed.

✅ Is it normal to bleed in the third week of pregnancy?

The bleeding that some women have at the end of the third week of gestation corresponds to implantation bleeding caused by the adhesion of the embryo to the endometrium. This bleeding is not very heavy, sometimes it is simply spotting that lasts one or two days. If it is heavy bleeding, it could be due to an early menstruation.

✅ Can morning sickness start at 3 weeks?

Morning sickness usually starts at about six weeks, but it can start as early as four weeks, or around the time that your period would be due. A few women experience nausea even earlier than this. It’s called morning sickness, but it can affect you at any time of the day.

What to Expect Your 3rd Week of Pregnancy - Video

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