The Sixth Week Pregnancy: Embryo Evolution and Symptoms (2024)

During the sixth week of pregnancy, the embryo implanted in the uterus begins to grow very rapidly and all its organs begin to develop from primitive structures.

The most important embryonic development event during this sixth week is the formation of the primitive heart, which begins to beat and pump blood throughout the body of the fetus.

The future mother's body also continues to undergo great changes to adapt to pregnancy. However, it is possible not to feel any symptoms of pregnancy yet.

Baby Development

Although at the beginning of the sixth week of pregnancy the embryo is still very small (it measures about 2-4 mm), it begins to undergo great changes and to increase its size quickly. At the end of this week, it will measure about 5-6 mm and can be seen on an ultrasound.

These measurements correspond to the Crown-to-Rump Length (CRL), which is the length from the head to the end of the spine. The measurement of the legs is not taken into account, as they are bent and this could lead to a bias in the measurement.

In addition, the heart of this small baby also begins to form during this week 6 of pregnancy. He only has two blood vessels, but he's already starting to beat very vigorously.

The heart of the fetus beats very fast, much faster than in an adult. On the first ultrasound, it is possible to hear the heartbeat at about 150 beats, which is completely normal.

The appearance of the embryo during the 6th week of pregnancy is a little strange.

His/her head is very large and appears curved towards its body. The rest of the changes that the fetus undergoes during its development are discussed below:

• The neural tube, from which the brain and spinal cord form, begins to close.
• In the middle part of the embryo is outlined an intestine, origin of the entire digestive system.
• Inside the embryo begins the formation of the lungs and muscle fibers.
• The primordiums of the eye and ear are formed, which are observed as black spots on both sides of the head.
• The extremities are not well appreciated, but small protuberances appear that will form the arms first and then the legs.

During this embryonic stage most organs are formed throughout the body. Therefore, there is an increased susceptibility to fetal malformations if the woman follows unhealthy lifestyle habits or does not take care of herself from the beginning of her pregnancy.

The placenta has not yet fully formed and the umbilical cord still does not provide the necessary nourishment for the development of the fetus. This nutritional contribution is given by the vitelline vesicle, an embryonic annex that will disappear when the placenta is formed.

Usual symptoms by the sixth week

At this time of pregnancy, the fetus evolves and undergoes great changes, such as the formation of the circulatory system. All of this rapid development and growth in the mother's womb causes the woman to feel obvious symptoms of pregnancy, such as the following:

• Morning sickness or vomiting
• Increased fatigue and weakness
• Intolerance to certain smells or tastes
• Constipation
• Darkening of the skin
• Frequent urination
• Breast sensibility and enlargement
• Appearance of cravings
• Headache
• Nasal congestion
• Excessive Salivation
• Heartburn
• Constant mood swings

It is important to note that not all women have the same symptoms. In fact, some women say they have no symptoms by the sixth week of pregnancy.

What does happen inside a woman's body are changes to adapt her bone structure and organs to her new state of pregnancy.

These changes also modify, in a more or less perceptible way, the rhythm of breathing, the woman's metabolism, blood circulation, the functioning of the liver and intestines.

In addition, the change that is going to start to be most significant from this week 6 is weight gain and belly growth.

The first ultrasound

The first trimester ultrasound confirming pregnancy should be done as early as week 6 or 7 of pregnancy. It is not advisable to do it sooner because it is possible that the embryo is not yet seen inside the gestational sac, which generates some stress in the woman to think that something is wrong.

Most women can already visualize the embryo with an abdominal ultrasound at the sixth week, as well as listen to the beats of the heart that has just formed. However, there are times when the heartbeat is not heard until the 7th week of pregnancy.

Assisted procreation, as any other medical treatment, requires that you rely on the professionalism of the doctors and staff of the clinic you choose. Obviously, each clinic is different. Get now your Fertility Report, which will select several clinics for you out of the pool of clinics that meet our strict quality criteria. Moreover, it will offer you a comparison between the fees and conditions each clinic offers in order for you to make a well informed choice.

When it is not possible to see the embryo and/or listen to its heartbeat, the woman will have to repeat the ultrasound ultrasound after one or two weeks to rule out the possibility that it is an anembryonic pregnancy.

It is also possible to discover in the 6 weeks ultrasound that it is a twin pregnancy. In the case of “non-identical” twins, two gestational sacs will be observed in the uterus. If they are “identical” twins, that is to say, they result from the division of an embryo, they can be in the same bag or in two different bags.

In addition to the ultrasound, during this first visit to the gynecologist, the woman will have to answer some questions in order to include them in her medical history. For example, if you already gave birth, if you have had voluntary or involuntary abortions, possible drug allergies, family history, if you have toxic habits, etc.

Care and recommendations

When a woman discovers that she is pregnant, there are many lifestyle changes that need to be made so as not to compromise the health of the baby or her own.

In this section, we will focus on recommendations to fight discomfort during the sixth week of pregnancy, as well as the most important care that women should think about:

• It is important to continue taking folic acid as the embryo's neural tube is beginning to close.
• Eat a healthy and balanced diet with legumes, fish, dairy products, meats, fruits and cereals.
• Eliminate undercooked or raw meats, sausages, and unpasteurized milk and cheese from the diet to avoid toxoplasmosis and listeriosis.
• It is not recommended to use laxatives to combat constipation. It can be compensated by drinking plenty of water, exercising daily and with fiber-rich foods.
• If vomiting is frequent during these weeks, a woman should eat a diet based on easily digestible foods, eat 5-6 meals a day, and drink plenty of water for hydration.
• Try not to drink too much water before going to bed to avoid getting up several times at night.
• Get adequate rest. If possible, it is advisable to take a short nap to be more active in the afternoon.
• Practice moderate sports and exercise such as yoga, pilates, swimming, or walking.
• To avoid breast discomfort, it is advisable to buy a comfortable bra, without earrings and made of cotton.
• Give up unhealthy habits such as coffee, alcohol, tobacco, or other drugs.

If you want to know more tips for taking care of your pregnancy and leading a healthy life, we recommend you read on in the next post: The Importance of Staying Healthy during Pregnancy.

FAQs from users

How long is the embryo at six weeks pregnant?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

Normally, the CRL of the embryo (measured from the skull to the end of the spine) is 2-4 mm in the sixth week of pregnancy. At this stage, the embryo grows at a rate of 1 or 2 mm per week. It is still very small and, even so, it already has a heart and it begins to pump its blood.

Is it normal to bleed in the sixth week of pregnancy?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

At the beginning of pregnancy it is possible to have small losses of blood without them being related to any problem. However, the bleeding may be due to an ectopic pregnancy or a threatened abortion by an intrauterine hematoma. Therefore, it is advisable to see a doctor in case of blood loss during the sixth week of pregnancy.

I'm 6 weeks pregnant and now the test is negative, what can it be?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

If after confirming the pregnancy with a positive blood test, the beta-hCG hormone begins to decrease or the pregnancy test is directly negative, it is because the woman has suffered a biochemical abortion or microabortion. The embryo stops developing in its first weeks and is expelled with bleeding that is sometimes even confused with menstruation.

Is it possible to see the embryo at the sixth week of pregnancy?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

Yes, in most cases, it is possible to see the embryo inside the gestational sac on an ultrasound scan with 6 weeks of pregnancy, both naturally and by in vitro fertilization (IVF). However, on some occasions, the gestational sac is observed without an embryo, which may indicate two things: the embryo is still very small and cannot be seen or, on the other hand, it is an anembryonic pregnancy.

In case of doubt, it will be necessary to repeat the ultrasound after one or two weeks, at which time it is possible to confirm that there is a heartbeat and that the pregnancy is evolutionary. If, unfortunately, the gestational sac was empty and it was an embryonic pregnancy, it would be necessary to perform a curettage if the gestational sac was not expelled with spontaneous bleeding.

I'm 6 weeks pregnant, can I have sex?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

Yes, as long as they are not contraindicated by the doctor due to a risky pregnancy or something similar. In pregnancies that evolve in a normal way, there are no problems in maintaining sexual relations as usual. The fetus does not suffer any damage since it is protected by amniotic fluid and, in addition, the uterus is sealed by the mucous plug.

Suggested for you

Soon you will be in the seventh week of pregnancy and the embryo will continue to increase in size. On the other hand, if you want to continue reading about embryonic and fetal development, we recommend you enter the next post: The Seventh Week of Pregnancy

If you've just discovered that you have a multiple pregnancy and two babies are on their way, you may want to read the following article: Fraternal Twins vs. Identical Twins – What’s the Difference?