Twelfth Week of Pregnancy: the first trimester comes to an end

By (embryologist).
Last Update: 07/31/2023

The 12th week of pregnancy is the last week of the third month of gestation. Therefore, this week marks the end of the critical first trimester, the stage where the risk of miscarriage is highest.

From now on, the mother will begin to enjoy her pregnancy more, feel more relaxed and have fewer bothersome symptoms. On the other hand, you will also notice how your belly and weight will increase as your pregnancy progresses.

How is the fetus doing in the 12th week of pregnancy?

At 12 weeks of pregnancy, the fetus has practically all its limbs and internal organs already formed. His face has a human profile, more rounded, and his chin has grown.

The size of the fetus at 12 weeks is 5-6 cm and its weight reaches 8-14 g.

At this point, a stage characterized by rapid growth and maturation of all systems begins. Some changes that the fetus undergoes at twelve weeks are as follows:

  • The intestines move into the abdominal cavity, where there is already space for them.
  • The kidneys begin to produce urine that is stored in the bladder.
  • Vocal cords and fingernails are formed.
  • The pituitary gland of the brain begins to secrete many hormones.
  • The first hair appears on the fetus.
  • The ears have almost reached their final position on both sides of the face.

In addition to all this, the fetus can already move very quickly, stretching its arms and legs, opening and closing its mouth, stretching its neck, etc.

On the other hand, the genitalia of the fetus already have male or female characteristics depending on the established sex, although they are not yet fully developed. The changes that can be seen depending on whether the baby is going to be a boy or a girl are as follows:

Male gender
the scrotum and glans penis begin to form.
Female gender
the clitoris, labia majora and labia minora have formed.

Despite this, it is not always possible to determine the sex of the fetus at the 12-week ultrasound.

Symptoms in the mother

Most pregnant women no longer feel nausea after 12 weeks of pregnancy. However, the high level of hormones such as estrogen and progesterone still results in changes in the expectant mother's body, such as the following:

  • Nails and hair grow faster and become stronger.
  • Increased production of sebaceous glands, resulting in brighter and fresher looking skin. Acne is also possible.
  • Increased blood flow. This can lead to the appearance of arachnoid nevus on the chest and legs: dilatation of a group of small arterioles arranged in a radial pattern.
  • Nasal congestion and/or small nosebleeds.
  • Increased risk of chloasma gravidarum: sun spots on the skin.
  • Breast enlargement, increased sensitivity and darkening of the aureoles.
  • The uterus begins to protrude from its location between the pelvic bones.
  • Heartburn and burning sensation in the esophagus, which may result in severe burning.
  • Abdominal and leg cramps due to compression of the uterus on the veins.

At this stage of pregnancy, some women feel more beautiful or uglier. Some notice that their bellies have grown considerably, while others have hardly any belly at all. As can be seen, the variety of symptoms, feelings and moods is enormous.

12-week ultrasound

Although the mother-to-be may have already had an ultrasound to confirm the pregnancy, the 12-week ultrasound is the first important ultrasound in gestation.

Ultrasound examinations can be performed via the abdominal or vaginal route, as considered by the gynecologist.

This visualization of the uterus, and especially of the fetus, will allow the assessment of a multitude of parameters and information regarding:

Fetal vitality
the fetus is found to be alive and has a heartbeat.
Number of fetuses
the number of fetuses is counted and, in case of twin or multiple pregnancy, it is checked whether the fetuses share placenta or amniotic sac.
Weeks of gestation
the cranio-caudal length (CRL), which is the distance between the crown of the head and the end of the fetal spine, is measured. With this, the gestational age of the fetus is definitively fixed and the approximate delivery date is calculated.
Anatomy of the fetus
although the sensitivity for detecting fetal malformations is low, it is possible to detect short limbs, severe brain anomalies, etc. Detailed study of the fetal morphology is performed at the 20-week ultrasound.
Risk of chromosomal abnormalities
nuchal translucency is measured and, together with other blood test parameters, the so-called combined first trimester screening or triple screening is performed. This allows an estimation of the risk of suffering chromosomal alterations such as Down syndrome, Edwards' syndrome or Patau's syndrome.
Maternal genital apparatus
the mother's uterus and ovaries are examined to rule out the presence of fibroids, cysts or tumors.
Preeclampsia screening
the pulsatility index in the uterine arteries is measured to try to determine the risk of developing arterial hypertension in the second half of pregnancy.
Ovular adnexa
the placenta, the umbilical cord and the amount of amniotic fluid are assessed to determine abnormalities such as placenta previa, olgohydramnios, rupture of the sac, etc.

As mentioned above, the appearance of the fetus in this twelfth week will be similar to that of a newborn. It is possible to clearly distinguish the head, thorax, abdomen, spine and extremities. Exceptionally, the specialist will be able to give information about the sex of the future baby, although not with 100% certainty.

Recommendations in the 12th week of pregnancy

Most women and couples take advantage of the results of the first trimester ultrasound to tell their friends and family about the baby on the way.

At this moment, a very happy stage of pregnancy begins, with less discomfort and more illusions. However, it is important that the woman does not stop paying attention to her first trimester care.

Therefore, we will continue to point out some interesting tips for pregnant women at 12 weeks:

  • Start wearing comfortable and loose-fitting clothing.
  • Continue with a healthy and balanced diet, rich in all the nutrients that are beneficial for pregnancy.
  • Drink plenty of water, at least 2 liters per day, for proper hydration.
  • Take vitamin supplements as recommended by the physician.
  • Take care of oral hygiene, since the risk of suffering gingivitis is higher.
  • Doing some physical activity, such as walking, yoga or swimming, helps to strengthen the muscles and relieve pain.
  • Use sunscreen with a high protection factor and do not sunbathe for a long time to avoid the appearance of spots on the skin.
  • Reduce the consumption of caffeine and carbonated beverages, as well as avoid alcohol and tobacco completely.
  • Take care of your posture and, when bending, bend your knees and keep your back straight to avoid hurting yourself.
  • Do not carry too much weight.

You can get more detailed information about all this in the following article: Health in pregnancy.

FAQs from users

What pregnancy complications can occur in the first trimester?

By Xinxin Lin MD (gynecologist).

The most common complications during the first trimester of pregnancy are haemorrhage and hyperemesis.
Read more

What is 12 weeks of pregnancy?

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

The twelfth week of pregnancy corresponds to the last week of the third month of gestation and is also the end of the first trimester of pregnancy, making it one of the most important weeks of pregnancy.

How is the baby at 12 weeks of pregnancy?

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

The foetus is 5-6 cm long in the twelfth week of pregnancy. It has doubled in size compared to the previous week and weighs about 8-14 g. All its internal and external structures are almost fully formed and are now beginning to mature and function.

In the ultrasound scan of week 12, it is possible to see his arms and legs with his hands, feet and all his little fingers and toes. His face is already very similar to that of a newborn baby, as are his chest, abdomen and back.

Is it possible to do a 4D ultrasound in the 12th week of pregnancy?

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

It is possible to do a 4D ultrasound from the twelfth week of pregnancy, but it is advisable to do it between the 24th and 30th week of gestation, as this is when the best images are obtained.

Suggested for you

You will soon be 13 weeks pregnant, at the beginning of the second trimester of gestation. For all the detailed information about this week, you can access the following post: Week 13 of pregnancy.

We remind you that physical exercise is very important during pregnancy, unless contraindicated by a doctor. If you want to know what sports you can practice, you can continue reading here: Physical exercise in pregnancy.

We make a great effort to provide you with the highest quality information.

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Alexandra Bouariu, Anca Maria Panaitescu, Kypros H Nicolaides. First Trimester Prediction of Adverse Pregnancy Outcomes-Identifying Pregnancies at Risk from as Early as 11-13 Weeks. Medicina (Kaunas). 2022 Feb 22;58(3):332. doi: 10.3390/medicina58030332 (View)

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Samantha F Ehrlich, Assiamira Ferrara, Monique M Hedderson, Juanran Feng, Romain Neugebauer. Exercise During the First Trimester of Pregnancy and the Risks of Abnormal Screening and Gestational Diabetes Mellitus. Diabetes Care. 2021 Feb;44(2):425-432. doi: 10.2337/dc20-1475. Epub 2020 Dec 21 (View)

Wanda Forczek, Agata Masłoń, Barbara Frączek, Marta Curyło, Marcin Salamaga, Agnieszka Suder. Does the first trimester of pregnancy induce alterations in the walking pattern? PLoS One. 2019 Jan 16;14(1):e0209766. doi: 10.1371/journal.pone.0209766. eCollection 2019 (View)

FAQs from users: 'What pregnancy complications can occur in the first trimester?', 'What is 12 weeks of pregnancy?', 'How is the baby at 12 weeks of pregnancy?' and 'Is it possible to do a 4D ultrasound in the 12th week of pregnancy?'.

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 Zaira Salvador
Zaira Salvador
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Technical University of Valencia (UPV). Biotechnology Degree from the National University of Ireland en Galway (NUIG) and embryologist specializing in Assisted Reproduction, with a Master's Degree in Biotechnology of Human Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI) More information about Zaira Salvador
License: 3185-CV

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