During this week, when the embryo is implanted, you can take a pregnancy test because it is very possible that you will be positive if you are pregnant.

Fourth week of pregnancy. The most important:

You are in the fourth week of pregnancy. During this week, the embryo will implant in your endometrium and begin to produce beta-hCG (which will be what makes the pregnancy test positive).

Week 4 of pregnancy (Week 2 of gestation).

You may already start to notice some of the early pregnancy symptoms. If you feel morning sickness, the ginger infusion is useful to calm them.

During this week you will have the first fault. Therefore, from this day on is the ideal time to take a pregnancy test. Remember: always in the morning and with the first urine.

If your pregnancy test has come back positive, congratulations. It is a good time to start organizing yourself, but calmly. If you go to your gynecologist for the first pregnancy check-up, you will go to the consultation of the midwife or midwife, who will be the one who controls you throughout the pregnancy.

As we knew in week 3 of pregnancy, ovulation tends to actually occur between the end of the second week and the beginning of the third, so if we take into account that the fertile period ranges from the 3 days before ovulation and In the 3 days after, in most cases,  conception takes place at some point in the third week of pregnancy (we must not confuse it with the week of gestation, which will always be 15 days behind the week of pregnancy).

In this way, the fourth week of pregnancy is actually the last week of the menstrual cycle, which means that it is the week in which the menstrual delay is likely to occur that can make you suspicious about the possibility that you are pregnant.

During this week, the embryo implants in the endometrium, which consists of the inner uterine layer. In fact, due to this implantation, you may have slight bleeding, which is what medically occurs as implantation bleeding or implantation bleeding.

The development of the embryo in the fourth week of pregnancy

During this week and until implantation occurs, the embryo is still a blastocyst, which means that it is still in an early stage, consisting of a complex cellular structure made up of around 200 cells.

However, it already has 2 well differentiated structures. On the one hand, we find the internal cell mass (ICM), which is from which the baby itself will develop, and on the other, the so-called trophoblast, from which the placenta will develop.

As we indicated, during this week the embryo implantation takes place, which basically consists of the adhesion (or ‘grip’) of the embryo to the endometrium. It is a much more complex process than you think, and this allows it to receive both the oxygen and the nutrients necessary for its development.

This implantation occurs around the seventh or eighth day of development of the embryo, and can last several days, which means that if we compare it with the regular menstrual cycle of 28 days, it will take place between 7 to 10 days after ovulation has occurred.

What changes and symptoms occur in a woman during week 4 of pregnancy?

During this week it is much more possible that the first symptoms of pregnancy are much more evident, although  the most common is to also confuse them with premenstrual symptoms, so in reality you may think that menstruation is about to arrive for a moment to another.

But when symptoms appear, the most common are the following:

  • Tension in the chest and tenderness in the breasts.
  • Morning sickness (especially in the morning).
  • Fluid retention and / or a strong urge to urinate.
  • Increased tiredness and sleep.
  • Pain in the lower abdomen.

In addition, as we indicated at the beginning, implantation bleeding may arise. However, we must take into account from the outset that bleeding does not always appear, so that a woman may not see signs of implantation (such as light bleeding), and yet be perfectly pregnant. Likewise, if the bleeding does not appear, this does not mean that the embryo has not implanted correctly.

If it appears, it is basically a light bleeding, so light that sometimes it can even go unnoticed. In fact, at times it may be a simple, minor staining.

Can I take a pregnancy test now?

We must bear in mind that we are in week 4 of pregnancy, and in the second week of pregnancy, which means that the embryo is already more than one week old. In it, different changes have already taken place in both its size and structure, going from being a cell that has divided into many to become what it is at the moment. And, all this, on the way from the fallopian tubes to the uterus.

In this week the embryo implantation takes place, and from the moment in which the implantation is completed, the embryo begins to produce the beta-hCG hormone, so if you take a pregnancy test it can be positive. What’s more, at the end of this week the menstrual delay will take place that could make you suspect a possible pregnancy.

When is the best time to take the pregnancy test?

Regarding when is the best day and time to perform the typical pregnancy test that you can easily buy in pharmacies, it is best to wait for the first day of absence, especially if you suspect that you may be pregnant.

That is, waiting for you one day after the time when your period should have arrived, especially if your menstrual cycles tend to be regular. However, there are brands that even offer the possibility of taking the test a day before the day of the arrival of menstruation, or the same day, with a fairly high reliability (around 95-98%).

So, if you plan to take the pregnancy test, remember that the best time of day to take it is always in the morning, collecting the first urine in the morning. This is because your body expels the hormone chorionic gonadotropin through the urine, and during these hours it tends to be more concentrated in the urine.

Doubts that may arise during the fourth week of pregnancy

Is it still too early to perform the first ultrasound?

Although the pregnancy test has given you positive, you must bear in mind that the gestation period -that is, the development of the embryo- is between 10 to 15 days less, so it is still too early to be able to see the embryo.

In any case, it could be possible to visualize the gestational sac, and due to the small size of the embryo, not see anything inside. This can obviously lead to confusion and create nervousness and tension for mom and dad.

It could also be due to the existence of an anembryonic pregnancy (hollow egg ), so it is still too early to confirm if it is a confusion because the embryo is still very small, or because the pregnancy is bad and the embryo has not developed.

Therefore, it is not advisable or advisable to perform an ultrasound scan during the fourth week of pregnancy.

At 4 weeks, can the pregnancy test be negative?

During this week the implantation of the embryo takes place. So if we take into account that the beta-hCG hormone begins to be generated from the moment the embryo implants in the endometrium, if it has been conceived but has not yet been implanted, a false negative is possible.

This happens in most cases when the urine pregnancy test is performed very early: a few days earlier than recommended (for example, before the day on which the period should theoretically arrive).

Therefore, it is advisable to repeat the pregnancy test a few days later, if you continue with a delay and your menstruation has obviously not reached you.


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