Week 18 of pregnancy: How big is the baby? Tips for mother

By (embryologist).
Last Update: 11/15/2023

The 18th week corresponds to about 4 and a half months of pregnancy and both the woman and the baby begin to undergo obvious changes. In the ultrasound of the 18th week of gestation it will be possible to observe the baby sucking its thumb and smiling.

It is possible that, if the woman has not already done so, she may begin to notice her baby's movements. In addition, the uterus increases in size, so the mother-to-be will have a bigger belly.

What does the baby look like in the 18th week of pregnancy?

Your child is testing his reflexes: he sucks, kicks and makes squeezing movements. The heart is already beating strongly because the cardiac chambers are delimited. The four chambers of the heart (two atria and two ventricles) are formed, as well as the four heart valves.

While in the womb the fetal blood flow in the heart works differently, some of the blood passes directly from the right atrium to the left atrium through an orifice called the foramen ovale, to prevent the blood from passing through the lungs. When the baby is born this hole closes.

The skeleton also follows its course and bone tissue begins to form, what was previously formed by cartilage begins to ossify forming bones, at the same time cartilage grows.

At the end of this week the future baby is about 14-15 cm long and weighs approximately 150-200 grams. However, there is no need to worry too much about the size of the baby, as each baby evolves differently.

Changes and symptoms in the mother

The woman will have gained a few pounds by the 18th week of pregnancy and will notice that her breasts are larger. In addition, it is possible that the woman's lumbar spine may be strained, or she may have some back pain. This is because you have changed your posture to maintain the new balance.

From this moment on, the woman will begin to urinate more frequently and even have to get up at night to go to the bathroom. The explanation is that the uterus is compressed over the bladder, which increases the frequency of urination. The woman is also likely to suffer from constipation as a result of the enlarged uterus, which compresses the intestines and hinders intestinal transit. Digestion is slower and heavier.

Other symptoms that a woman will notice in the 18th week of pregnancy include the following:

  • Spots on the face.
  • Burning.
  • Sciatica.
  • Whitish discharge.
  • Dizziness.

In addition, the color of the areolas and nipples begins to darken. This will make it easier for the baby to latch on when breastfeeding begins.

Tips for coping with week 18

Some pregnant women experience unpleasant discomfort in addition to heartburn. One recommendation to alleviate stomach reflux is to eat less food and chew everything well. In addition, it is advisable to avoid fatty and spicy foods.

Healthy habits should be followed throughout the pregnancy, avoiding alcohol and tobacco. You should also eat a balanced diet to reduce the risk of constipation.

FAQs from users

How far along is the 18th week of pregnancy?

By Marta Barranquero Gómez B.Sc., M.Sc. (embryologist).

Week 18 is part of the fifth month of pregnancy and, therefore, of the second trimester of gestation.

What is the size of the baby in the 18th week of pregnancy?

By Marta Barranquero Gómez B.Sc., M.Sc. (embryologist).

Each baby may develop differently, but it is usual for the baby to be around 13-14 cm and weigh about 150-200 grams by the 18th week of pregnancy.

Can you tell if it is a boy or a girl in the 18th week of pregnancy?

By Marta Barranquero Gómez B.Sc., M.Sc. (embryologist).

Yes, but it is also possible to know from the 15th week of pregnancy through an ultrasound. However, if it is a twin pregnancy, it is more complicated to know the sex of the babies, since they could cover each other. Therefore, it will depend on when the ultrasound is done and how calm the babies are.

Suggested for you

If you want to know more about the changes of the next week of gestation, we recommend you to visit the following article: Week 19 of pregnancy.

If you are interested in information about the sixth month of pregnancy, you can visit this link: 6 months of pregnancy: characteristics and symptoms.

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M Fambrini 1, C Penna, M G Fallani, A Pieralli, A Mattei, G Scarselli, G L Taddei, M Marchionni. Feasibility and outcome of laser CO2 conization performed within the 18th week of gestation. Int J Gynecol Cancer
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Moacyr J B M Rêgo, Antônio F Silva Filho, Ana P V Sobral, Eduardo I C Beltrão. Glycomic profile of the human parotid gland between 18th and 26th week of fetal development. J Oral Sci. 2016;58(3):353-60. doi: 10.2334/josnusd.15-0299 (View)

FAQs from users: 'How far along is the 18th week of pregnancy?', 'What is the size of the baby in the 18th week of pregnancy?' and 'Can you tell if it is a boy or a girl in the 18th week of pregnancy?'.

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 Marta Barranquero Gómez
Marta Barranquero Gómez
B.Sc., M.Sc.
Graduated in Biochemistry and Biomedical Sciences by the University of Valencia (UV) and specialized in Assisted Reproduction by the University of Alcalá de Henares (UAH) in collaboration with Ginefiv and in Clinical Genetics by the University of Alcalá de Henares (UAH). More information about Marta Barranquero Gómez
License: 3316-CV

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