Week 17 of pregnancy: What changes in the woman and the fetus?

By (embryologist) and (psychologist).
Last Update: 02/24/2022

The 17th week of pregnancy corresponds to the beginning of the fifth month of pregnancy. The woman is in the second trimester of pregnancy and is getting closer to the halfway point.

As the fetus continues to develop, changes in the body and weight gain (around 2.5-4 kg) of the expectant mother begin to become more evident. It is quite possible that in the 17th week it is already beginning to be noticeable that the woman is pregnant.

Fetal development

At this 17th week of pregnancy, the fetus measures about 13 cm and may weigh about 140 g. As the weeks of gestation pass, the fetus becomes more and more similar to a newborn baby.

Among the most important changes that occur for the fetus in week 17, we can mention the following:

  • The various organs and systems continue to develop.
  • The cartilaginous skeleton gradually hardens.
  • Your heartbeat can now be heard with a stethoscope.
  • It accumulates adipose tissue, which is important for body heat.
  • It is possible for the fetus to react to loud sounds, as it is able to perceive these stimuli due to its developing hearing.
  • Hair begins to appear on the eyelashes, eyebrows, and above the upper lip.
  • It is actively moving inside the uterus, although it is common that the pregnant woman does not notice anything yet. It is common for the expectant mother to start noticing the baby a little later, from the 18th week of pregnancy.
  • Caseous vernixappears. It is a whitish fatty substance that coats and protects the skin of the fetus. Vernix caseosa can sometimes be seen, to a greater or lesser extent, even in the newborn.

On the other hand, it is possible that if the pregnant woman has an ultrasound in this 17th week, they can tell her the sex of her baby and she will be able to know if it is a boy or a girl.

Changes in the mother-to-be

The fifth month of pregnancy is beginning and, during the 17th week of gestation, it is very possible that the woman has already observed certain changes in her body, as well as other signs.

Body changes

During the 17th week, the pregnant woman will have begun to notice changes in her waistline or abdomen. The pregnant woman's waistline usually widens and gradually disappears. In addition, the lower abdomen will be more voluminous.

This means that the woman will have started to show that she is pregnant, especially if she is very thin. The woman may even have begun to change her posture to maintain balance with the growing belly. However, other women do not have such noticeable symptoms even at 17 weeks gestation.

Because of these changes your body is undergoing, it is a good time to start wearing maternity clothes. Perhaps this type of pants is still a little wide, but the pregnant woman will be more comfortable because it is possible that she will begin to have problems putting on her usual clothes.

The pregnant woman at this time will also notice the development of her breastsmore. The breasts increase in size and will receive more blood supply, so the veins become more visible. The breast is getting ready to produce milk and breastfeed the baby in a few months. Because of this, the pregnant woman may begin to need bras with a larger cup size.

Other changes

In addition to bodily changes, the pregnant woman may begin to notice other signs such as the following:

  • Some discomfort in the abdomen due to the uterus increasing in size. Some positions may be more uncomfortable than others because they strain the ligaments that are supporting the uterus.
  • More frequent urination, since the uterus is larger, presses, and leaves less space for the bladder.
  • Cramps, especially in the legs. These symptoms may be due to the nerves being compressed by the uterus. Another possible cause of this discomfort is altered peripheral blood flow, fluid retention, and decreased potassium and calcium levels.

On the other hand, it is common for stretch marks to appear on the pregnant woman's skin during this period. Stretch marks are very common on the belly and chest and it will be very important to start preventing them with appropriate creams.


In the 17th week of gestation, as throughout the entire pregnancy, it is very important to take care of your diet. The diet must be varied, balanced, and provide the different types of nutrients, as well as other molecules necessary for the mother and the development of the fetus. In addition, it is especially important to maintain good hydration. This can be achieved not only by drinking water but also by eating, for example, fruits that will also provide nutrients and vitamins.

It is also advisable to exercise, adapted to pregnancy and provided it is not contraindicated, or, at least, for the pregnant woman to walk.

A diet rich in fiber, proper hydration, and exercise will help to reduce constipation that may appear at this stage of pregnancy and to avoid the presence of hemorrhoids.

However, it is essential to follow the indications of the specialist who monitors the pregnancy, so that everything develops in a correct way and to avoid risks.

Pregnancy control.

One of the tests that can be done when a pregnancy has reached the 17th week is amniocentesis.

This is an invasive test that uses a needle to collect a sample of the amniotic fluid surrounding the baby through the abdomen. This amniotic fluid contains cells that come from the fetus and can be analyzed to check whether the fetus has, in particular, any genetic alterations.

You can read more about amniocentesis at this link: Amniocentesis: what are its indications and possible risks?

FAQs from users

Can I know the sex of the baby in the 17th week of pregnancy?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

In the 17th week, it is possible that they can already tell you the sex of the baby. However, in the Social Security, this ultrasound is performed a little later, around the 20th week of pregnancy.

However, there are other methods by which the sex of the baby can be known as early as week 17.

Can I sleep on my stomach in the 17th week of pregnancy?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Due to the changes your body is undergoing in your abdomen, it is very possible that you will no longer be able to sleep on your stomach in the 17th week of pregnancy because you will be very uncomfortable.

Is it normal that in week 17 of pregnancy I can't feel my belly or my baby?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Yes, every pregnancy is different. For some women it will be very noticeable that they are pregnant at week 17, while for other women it may not be so obvious yet. Also, it is common to begin to feel the baby's movements in the next few weeks of pregnancy.

However, if you are worried, you can go to a specialist to check that everything is fine, so you can rest assured.

Are there contractions in the 17th week of pregnancy?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Although they are more frequent in the second half of pregnancy, Braxton Hicks contractions may occur in week 17.

These contractions are physiological and do not have a regular interval between contractions (unlike labor contractions). Although not painful, Braxton Hicks contractions are uncomfortable.

However, if in doubt, you should always consult your obstetrician.

If you are 17 weeks pregnant, you may be interested in learning more about the 18th week of pregnancy. To do so, you can visit the following link: Week 18 of pregnancy

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Bamalan OA, Menezes RG. Vernix Caseosa. 2020 Jul 2. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–.

Cabanyes, J. El comportamiento fetal: una ventana al neurodesarrollo y al diagnóstico temprano. 2014 Sept. Pediatría Atención Primaria vol.16 (63).

Nizard J. Amniocentesis: technique and education. Curr Opin Obstet Gynecol. 2010 Apr;22(2):152-4.

FAQs from users: 'Can I know the sex of the baby in the 17th week of pregnancy?', 'Can I sleep on my stomach in the 17th week of pregnancy?', 'Is it normal that in week 17 of pregnancy I can't feel my belly or my baby?' and 'Are there contractions in the 17th week of pregnancy?'.

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 Silvia Azaña Gutiérrez
Silvia Azaña Gutiérrez
B.Sc., M.Sc.
Graduate in Health Biology from the University of Alcalá and specialized in Clinical Genetics from the same university. Master in Assisted Reproduction by the University of Valencia in collaboration with IVI clinics. More information about Silvia Azaña Gutiérrez
License: 3435-CV
Adapted into english by:
 Cristina  Algarra Goosman
Cristina Algarra Goosman
B.Sc., M.Sc.
Graduated in Psychology by the University of Valencia (UV) and specialized in Clinical Psychology by the European University Center and specific training in Infertility: Legal, Medical and Psychosocial Aspects by University of Valencia (UV) and ADEIT.
More information about Cristina Algarra Goosman
Member number: CV16874

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