By Cristina Mestre Ferrer BSc, MSc (embryologist).
Last Update: 02/06/2015

During the first 5 months of pregnancy an important development of the internal organs of the fetus occurs. For example, the circulatory system is already very evolved, the ventricles of the heart are well defined and the heart is able to beat with intensity. The baby’s face has not yet acquired a round shape and his eyes are closed and very prominent.

During this stage of the pregnancy there will probably be some times when you will not feel the baby and it will seem like he is asleep. This happens because when you are standing the baby doesn’t have as much freedom of movement because he is insert in the pelvis. When you are lying down, on the other hand, the baby can move with a lot of strength and intensity.

The different sections of this article have been assembled into the following table of contents.

General changes by week

5 months of pregnancy correspond to 20 weeks, starting at 17 weeks of pregnancy, totaling 4 weeks of the fifth month. We will analyze each week in detail next:

Week 17

The vernix, the fat substance that protects and covers your baby’s skin, as in the case of lanugo, begins to gradually disappear until the pregnancy comes to an end. Normally at the time of childbirth the vermix has disappeared completely.

The fetus looks more and more like a newborn baby, though his head is still somewhat deformed. Logically, the development of the fetus causes an increase in both the baby’s and the mother’s weight. The baby should measure around 12cm and weight 100 grams.

During this week you will be able to notice a few changes in your breasts, given that the hormones are preparing so you are able to produce breast milk. The mammary glands grow in size and the veins are more noticeable. You might have to buy new bras that correspond to your new breast size and that make you comfortable.

You can read this article about the 17 weeks of pregnancy.

Week 18

During this week, the baby’s weight increases around 50g and he grows about one centimeter.

The baby’s heart continues to develop and its four chambers are formed. Meanwhile, the baby’s skeleton is also developing and the bone tissue starts to grow. The cartilage grows at the same time as the bone tissue.

The mother to be might need to urinate more frequently and experience some constipation. Both these symptoms are normal and typical of this stage of the pregnancy so you should not worry nor mistake these symptoms for the symptoms of a disease like cystitis.

Find more information in the article about about the 18th week of pregnancy.

Week 19

The baby’s weight makes you feel tired and heavy. From this point on you might feel like your legs are swollen. It is important to prevent varicose veins, which can easily appear during this stage of pregnancy. You don’t need to worry, though, because, nowadays, there are several creams that solve this little problem and that are available in the marked.

During this week the baby moves a lot so you will be able to feel his movements. You will also be able to hear the baby moving in your stomach and his or hers heartbeat. The moment you hear your baby’s heartbeat might be one of the most emotional moments of the pregnancy.

Important changes also happen in the baby’s brain. During these days thousands of neurons are created and the baby’s brain closely resembles that of an adult. The baby’s teeth also evolve quickly, the gums and first teeth are created.

Week 20

The skin of the mother to be is being stretched while her internal organs are compressed. This happens because the pelvis is located two fingers below the navel. The baby is growing and needs space.

The diet during a pregnancy should be controlled from the start, but it is important to pay special attention to it after this week. The mother will need many nutrients and a good dose of iron so the fetus can grow correctly. The mother needs to think the baby is now in full expansion and it’s important he grows well.

You can find more information in the article named 20 weeks pregnant.

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Authors and contributors

 Cristina Mestre Ferrer
BSc, MSc
Bachelor's Degree in Biological Sciences, Genetics & Human Reproduction from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Embryologist at IVI Barcelona. More information
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