In short: The abdomen begins to grow noticeably from about 16 to 20 weeks. The key measurable indicator is the height of the fundus of the uterus (SFH): normally, it approximately corresponds to the gestational age in centimeters. The size of the abdomen depends on many factors and is not a direct indicator of the health of the fetus - ultrasound gives an accurate assessment.
When the belly begins to grow
The uterus begins to enlarge in the first trimester, but during this period it is still in the pelvis and the abdomen is almost invisible from the outside. A slight "bulge" in the lower abdomen in the first trimester is more often bloating (a consequence of the action of progesterone), and not uterine growth.
By the 12th week, the uterus reaches the size of a grapefruit and rises to the pubic symphysis. It is from this moment that the doctor begins to measure the height of the fundus of the uterus (SFH) - the distance from the pubic symphysis to the top of the uterus.
For most women, the abdomen becomes visible to others around the 16th to 20th week. In those who have given birth again, it is a little earlier, since the abdominal muscles are already stretched by the previous pregnancy. In women with an asthenic physique, the abdomen may be noticeable earlier than in overweight women.
Norms for the height of the fundus of the uterus by week
The height of the fundus of the uterus is measured with a measuring tape from the upper edge of the pubic symphysis to the highest point of the uterus. A convenient rule: starting from the 20th week, the AMD in centimeters is approximately equal to the gestational age in weeks (±2-3 cm).
Approximate landmarks:
16 weeks – 14–18 cm
20 weeks – 18–22 cm
24 weeks – 22–26 cm
28 weeks – 26–30 cm
32 weeks – 30–33 cm
36 weeks – 32–37 cm
40 weeks – 35-38 cm (may decrease slightly as the head lowers)
16 weeks – 14–18 cm
20 weeks – 18–22 cm
24 weeks – 22–26 cm
28 weeks – 26–30 cm
32 weeks – 30–33 cm
36 weeks – 32–37 cm
40 weeks – 35-38 cm (may decrease slightly as the head lowers)
These figures are approximate. A deviation of 2-3 cm on both sides of the norm is, as a rule, a variant of the norm. An accurate assessment of the growth and development of the fetus is given only by ultrasound during pregnancy.
Abdominal circumference by week
Abdominal circumference (AB) is measured at the level of the navel. This indicator is more variable than ARMD, and depends on the physique, the amount of subcutaneous fat and muscle tone. Average values:
20 weeks – about 70–75 cm
28 weeks – about 80–85 cm
32 weeks – about 85–90 cm
36 weeks – about 90–95 cm
40 weeks – about 95–100 cm
20 weeks – about 70–75 cm
28 weeks – about 80–85 cm
32 weeks – about 85–90 cm
36 weeks – about 90–95 cm
40 weeks – about 95–100 cm
The size of the abdomen itself does not indicate whether the child is developing well. The dynamics is indicative: the abdomen should grow evenly from visit to visit, and not stop or increase sharply.
Why bellies are different
No two bellies look the same – even in the same woman in different pregnancies. Here are the main factors that affect the appearance and size of the abdomen:
Mother's physique and height. In tall women with a long torso, the uterus grows "deeper", and the abdomen looks smaller. In women of short stature, the uterus has nowhere to grow forward, and the abdomen looks larger. This has nothing to do with the size of the fetus.
Tone of the abdominal muscles. In the first pregnancy, the abdominal muscles are more elastic, and the abdomen looks neater and more protruding. In repeated pregnancies, the muscles are stretched and the abdomen appears larger and lower.
Number of fruits. In multiple pregnancies, the abdomen is much larger.
Amount of amniotic fluid. Polyhydramnios makes the abdomen larger, oligohydramnios - less than usual for this period.
Fetal position. Transverse or breech presentation changes the shape of the abdomen.
The size of the fruit itself. A larger fetus = a slightly larger belly, but the difference is not as big as it is commonly thought.
When does the abdomen droop and what does it mean
2-4 weeks before childbirth (in primiparous women) or a few days (in multiparous women), there is a "lowering of the abdomen" - the fetal head descends into the small pelvis. Visually, the abdomen shifts down. After that, it becomes easier for many women to breathe, but urination becomes more frequent and there is pressure in the perineum.
In multiparous women, the abdomen may not descend in advance - this is normal. Read more about preparing for childbirth and harbingers.
Abdominal skin care
As the abdomen grows, the skin stretches, which in some women leads to the appearance of stretch marks (striae gravidarum). They occur in the deep layers of the skin and it is impossible to completely prevent them with creams - genetics play a key role. However, regular moisturizing of the skin with oils (coconut, almond) or special creams improves its elasticity and reduces the severity of stretch marks.
Itching of the abdominal skin during pregnancy is a normal phenomenon associated with stretching. If the itching is very severe, yellowing of the skin or dark urine appears, consult a doctor: this may be a sign of intrahepatic cholestasis of pregnancy.
When to see a doctor
See a doctor if:
ARM deviates significantly (more than 3 cm) from the norm for your term.
The abdomen has stopped growing or has become noticeably smaller - there may be oligohydramnios or fetal growth retardation.
The abdomen grew very quickly in a short time - polyhydramnios is possible.
Severe itching of the abdominal skin, especially in the late stages.
Abdominal pain not related to fetal movements.
ARM deviates significantly (more than 3 cm) from the norm for your term.
The abdomen has stopped growing or has become noticeably smaller - there may be oligohydramnios or fetal growth retardation.
The abdomen grew very quickly in a short time - polyhydramnios is possible.
Severe itching of the abdominal skin, especially in the late stages.
Abdominal pain not related to fetal movements.
Frequently Asked Questions
Does a small belly mean a small child?
No. The size of the abdomen on the outside depends on the mother's physique, muscle tone and fetal position - and does not correlate well with the real weight of the child. Only ultrasound (fetometry) gives accurate information about the size of the fetus.
When does the belly become noticeable in the second pregnancy?
In repeated pregnancies, the abdomen becomes noticeable 2-4 weeks earlier than in the first. This is due to the reduced tone of the abdominal muscles.
Conclusion
The abdomen begins to grow noticeably from the 16th-20th week. The height of the fundus of the uterus is the main clinical benchmark that the doctor measures at each appointment. The size of the abdomen depends on individual characteristics and does not correlate well with the condition of the fetus - only ultrasound gives an accurate picture. Monitor the dynamics of growth, take care of your skin and consult a doctor in case of any alarming changes.
Bibliography
- WHO. WHO recommendations on antenatal care for a positive pregnancy experience. WHO, 2016. https://www.who.int/publications/i/item/9789241549912
- ACOG Practice Bulletin No. 134. Fetal Growth Restriction. Obstet Gynecol. 2013. https://www.acog.org/clinical/clinical-guidance/practice-bulletin
- Mongelli M, Gardosi J. Symphysis-fundus height and pregnancy dating. Int J Gynaecol Obstet. 2004. https://pubmed.ncbi.nlm.nih.gov/15099781/
- NICE. Antenatal care. NICE Guideline NG201, 2021. https://www.nice.org.uk/guidance/ng201
- Ministry of Health of the Russian Federation. Clinical recommendations: Normal pregnancy. Ministry of Health of the Russian Federation, 2023. https://cr.minzdrav.gov.ru/
This material is for informational purposes only and does not constitute medical advice and is not a substitute for medical advice. If a child's sleep is accompanied by alarming symptoms, a pronounced deterioration in health, problems with breathing, feeding or weight gain, it is necessary to consult a qualified medical specialist as soon as possible, and not rely only on information from the Internet.
