Is a 31-week pregnancy weighing 2kg normal or abnormal? Based on this week's fetal index, mothers will see that this is the standard weight for the 31 week baby.
The 31st week of pregnancy is one of the important moments in your baby's remarkable development.
Overall now the baby is over 40.6cm long and weighs about 1.5kg, about the size of a coconut. In just a few more weeks the weight of the fetus will reach its maximum, preparing for the upcoming birth of the baby.
However, depending on the physical condition and nutrition of the mother, sometimes this weight can be less or more than average.
To easily assess the health of the fetus, pregnant mothers should refer to the baby's development index through each day in this 31st week as follows:
Pregnancy index of 31 weeks + 0
Bipolar diameter (BPD): 72-84 mm, average 78mm
Femur Length (FL): 55-65mm, average 59mm
Waist circumference (AC): 245-311mm, average 278mm
Head Circumference (HC): 276-310mm, average 293mm
Estimated weight (EFW): 1453-2049g, average 1751g
Pregnancy index of 31 weeks + 1
Bipolar diameter (BPD): 73-85 mm, average 78mm
Femur Length (FL): 55- 66mm, average 59mm
Waist circumference (AC): 247-311mm, average 279mm
Head circumference (HC): 277-311mm, average 294mm
Estimated weight (EFW): 1477-2083g, average 1780g
Pregnancy index of 31 weeks + 2
Bipolar diameter (BPD): 73-85 mm, average 79mm
Femur Length (FL): 55-66mm, average 60mm
Waist circumference (AC): 248-311mm, average 279mm
Head circumference (HC): 278-312mm, average 295mm
Estimated weight (EFW): 1501-2116g, average 1809g
Pregnancy index of 31 weeks + 3
Bipolar diameter (BPD): 73-85 mm, average 79mm
Femur Length (FL): 55-66mm, average 60mm
Waist circumference (AC): 250-311mm, average 280mm
Head Circumference (HC): 279-313mm, average 296mm
Estimated Weight (EFW): 1525-2150g, average 1838g
Pregnancy index of 31 weeks + 4
Bipolar diameter (BPD): 74-86mm, average 80mm
Femur Length (FL): 56-67mm, average 60mm
Waist circumference (AC): 253-310mm, average 281mm
Head circumference (HC): 281-315mm, average 298mm
Estimated weight (EFW): 1549-2184g, average 1866g
Pregnancy index 31 weeks + 5
Bipolar diameter (BPD): 74-86mm, average 80mm
Femur Length (FL): 56-67mm, average 60mm
Waist circumference (AC): 253-310mm, average 282mm
Head circumference (HC): 282-316mm, average 299mm
Estimated weight (EFW): 1573-2218g, average 1895g
Pregnancy index 31 weeks + 6
Bipolar diameter (BPD): 75-87mm, average 81mm
Femur Length (FL): 56-68mm, average 61mm
Waist circumference (AC): 254-310mm, average 282mm
Head circumference (HC): 283-317mm, average 300mm
Estimated weight (EFW): 1597-2251g, average 1924g
If the indicators are out of the limit in the above table, the pregnant mother needs to discuss with her doctor in order to have a timely remedy as well as further testing of the risk factors for the fetus.
Based on the above indexes, mothers can see that 31 weeks fetus weighing 2kg is considered to reach the standard average.
In terms of weight, the baby is growing well. However, to assess the development of a fetus, in addition to weight, doctors also need to rely on other indicators (as shown in the table above), including head circumference, bipolar diameter, water volume. amniotic ... All these indicators will be reviewed during the mother goes supersonic .
According to obstetricians, 31 weeks is the last of 3 milestones of 3D, 4D ultrasound important to examine the condition of the fetus again.
This time, the doctor will look for some late abnormalities that have not been seen before, such as the heart, pulse, and brain structure.
In addition, ultrasound also helps to assess whether the fetus is age-appropriate, promptly detects the slow growth of the uterus, a cause of fetal failure and postpartum asphyxia, and determine more specifically the date of birth.
Therefore, if the pregnant mother feels worried about her baby's weight, ask questions and have a doctor check specifically during this ultrasound to make sure that the baby is growing well.
See more:
31 weeks gestation and the important parameters mothers need special attention
31-week election: Mother's body has major changes and birth contractions begin to appear
31 weeks fetus has turned yet, is there any way to help the fetus turn around?
Plan a free Chicago weekend for Oct. 9–11, 2026 with verified museum tours, library workshops, park events, markets and family activities, including hours, ages, registration, accessibility and transit notes.
Find verified free Chicago activities for kids in October 2026: library programs, Field Museum Wednesdays for Illinois residents, zoo visits, films, crafts, and park festivals with dates, ages, registration, access, and transit notes.
Fix bitter, sour, or weak coffee at home with a practical guide to beans, grind size, water, ratio, temperature, pour-over technique, and tasting.
Learn beginner-friendly winter houseplant care for light, watering, humidity, temperature, fertilizer, pests, and the mistakes that commonly damage plants.
Declutter your home without chasing perfection. Learn which spaces to tackle first, how clutter may affect stress and attention, and how to keep results manageable.
Discover which smart kitchen gadgets are genuinely useful, what to check before buying, how to set them up, and common beginner mistakes to avoid.
Functional beverages promise energy, hydration, gut support, protein, and more. Learn which benefits have evidence, what labels can hide, and how to choose wisely.
Learn practical zero-waste cooking habits that reduce food waste, stretch groceries, use leftovers safely, and turn edible scraps into useful meals.
Plan a cozy dinner party with the right guest count, make-ahead menu, warm atmosphere, food-safety basics, and a realistic hosting timeline.
Refresh your home for fall 2026 with budget-friendly decor trends, practical tradeoffs, and smart ways to add warmth, texture, and personality.
