18 January

Small for gestation (Low weight of the baby)

Many of my viewers are concerned about the weight of the fetus during their pregnancy. On an everyday basis, I get at least two to three questions from my subscribers, about this. Hence decided to write a blog on the weight of the fetus, what is normal and what is considered small for gestation.Every baby is different and babies grow at different rates from early pregnancy. The weight of the baby inside the uterus is calculated by a formula which takes in to account the head circumference, abdominal circumference,

fetal length and Bi-parietal diameter (which is the diameter of the head) of the fetus. These biometric values are usually recorded during your ultrasound examination. The machine assigns the estimated fetal weight taking these measurements and based on a formula. Alternatively, the doctor may compare the measurements with a growth chart to estimate fetal weight. This weight is also given a percentile score based on an international growth chart. As the weight depends on the estimated gestational age based on the last menstrual period,  sometimes if the menstrual cycles have been erratic before pregnancy, the estimated gestational age may not be accurate.

Another method to estimate the weight or growth of the baby is by measuring the fundal height. After 20 weeks of pregnancy, the height of the fundus (the top of a mother's uterus) can be measured from the pubic bone. This measurement in centimeters usually corresponds with the number of weeks of pregnancy. If the measurement is low for the number of weeks, the baby may be smaller than expected.

When the estimated fetal weight is below the 10th percentile for babies of the same gestational age, the baby is said to be small for gestational age.

Fetal growth can be hampered by various factors -

Some Factors relate to the mother’s health

- High blood pressure

- Chronic kidney disease

- Advanced diabetes

- Heart or respiratory disease

- Malnutrition, anemia

- Infection

-  Substance use (alcohol, drugs)

-  Cigarette smoking


Some factors are due to pregnancy


-  Decreased blood flow to the uterus and placenta


-  Placental abruption (placenta detaches from the uterus)


-  Placenta previa (placenta attaches low in the uterus)


-  Infection in the tissues around the fetus


Some factors could be due to the developing baby (fetus)


  • Twin pregnancy


  •   Birth defects


  •   Chromosomal abnormality


Because of these factors, the baby may not be able to receive proper nutrients and oxygen from the mother during pregnancy.  The growth and the development of the cells and tissues of the fetus are slowed or retarded, which is called intra-uterine growth retardation.

Some babies may be genetically small, as the parents are also small built. Thus, a single ultrasound measurement may not be able to definitely diagnose growth retardation, except in cases where the weight is below 10th percentile mark. When the doctor spots a pattern of slow growth in the baby or a decreasing weight in the baby through the pregnancy, she may see you more frequently, in order to monitor the weight of the baby, fetal well-being and the amount of amniotic fluid.


Doppler flow can be done to see the flow of blood in the umbilical cord, and the fetal brain.  A decreased flow could be indicative of Intra-uterine growth retardation

Pregnant women can increase anywhere from 8-16 kg during pregnancy. Small weight gains during pregnancy can indicate growth retardation in the baby.


Small for gestational age babies at birth may be weak and less able to tolerate large feedings or to stay warm. Treatment may include keeping them warm, tube feedings for a few days as they may be too weak to suck on their own, monitoring their sugar and oxygen levels.

Preventable factors lie to a certain extent on maternal nutrition and lifestyle changes. Pregnant mothers need to be educated about the importance of nutrition, exercise and prenatal vitamins during pregnancy.

Please use the chart below to compare the fetal weight. If the fetal weight is below the 10th percentile, it is cause for concern,  For example - If you are in the 32 nd week of pregnancy and the ultrasound report says the weight of the baby is 2 kg then it is almost 70th percentile weight, meaning 70% of the babies in 32nd week are around this weight, but if in 32nd week if the weight is say - 1.6 kg then it is close to 20 percentile...It is a cause for concern. It is considered small for gestation.  Please do not get stressed out with just one measurement, serial recordings are a better predictor. Always consult your doctor.



About our blogs

We have put together weekly developments during pregnancy. These articles are only for information. Every pregnancy is different and every woman's experience may be different. We also have articles relating to women's health, infertility and plan to add information about newborn care. Through the blogs, videos and our online consultation services, we are trying to empower mothers (as well as soon-to-be-moms) with health information which is easily understandable. Our mission is to help mothers have a happy pregnancy and a very happy postpartum experience. 

Have a passion to write, want to share a pregnancy story... Send in your articles, our team of experts will go through it and publish it on our website. 

Call us at +91 80 39534676  for a second opinion from our doctors. This is a paid service.

Pregnancy brings a new meaning to the concept of beauty to a woman. It is a period of immense joy, excitement and anxiety. The feeling of carrying a little soul within you is beautiful.

Last modified on Monday, 06 August 2018 10:09
Dr Padma

Dr Padma is a Family care physician and is the Founder and CEO of MedHealthTV.


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