Fetal Growth Chart
Important For Determining Fetal Growth

Fetal growth chart are made to assess the growth of the baby in the womb. It thereby helps to predict short and long term outcomes in a newborn baby. Though this sounds really good, the appropriateness of intrauterine growth estimation of fetuses has its limitations. The methods available for checking a baby's size in the womb, before it is born, provide only an estimated fetal weight and body measurements.

Fetal growth is a dynamic process. Its estimation requires serial evaluations of fetal size, each at 3 weeks interval : Shorter intervals could lead to some faulty interpretations. Moreover, it works on the assumption that growth is a uniform continuous process rather than sporadic.

These factors confuse the prediction of the expected outcome for neonates. Results of the various parameters evaluated for the fetal growth have to be correlated clinically.

The fetal growth charts are best as clinician's tools to judge the overall picture of an estimated fetal weight.

Methods of fetal length and weight assessment

1. Fetal Growth Charts

Fetal growth percentile charts need factual information on optimal intrauterine growth. This is only possible by sequentially evaluating the unborn babies of normal pregnancies. Normal here implies that the pregnancies should not only be free of maternal and fetal disease, but also not exposed to any biological or chemical threats to fetal growth and development. 

Limitations faced to accomplish such work

Data collection for appropriate intrauterine growth estimation of fetuses is full of difficulties for the reasons given below.

  • Well babies with the optimal intrauterine growth are never born premature.Therefore, the neccessary data to prepare fetal growth charts has to be accumulated by an alternative method.

  • Data collection for fetal growth charts is done from birth weight of the babies born at different gestational age and is approximated with ultrasound evaluations done prenatally.

  • Fetuses do not grow at the same rate and implications of percentile vary with the existing growth restricting factors in the source population.

  • There are many normal determinants of fetal development, and so the estimation of percentile position at the extremes of distribution graph gets imprecise.

2. Fundal Height of the Gravid Uterus

The fundal height of uterus of an expectant mother, when measured in centimeters, coincides with weeks of gestation between 18 and 30 weeks. If the measurement is more than 2-3 cm from the expected height, inappropriate fetal growth could be expected.

Factors that affect clinical measurement of the uterus

  • Mother's weight and height
  • Uterus thickness
  • Size of the placenta
  • Amniotic fluid content of the uterus

These factors, which are a common variable, significantly affect the correct estimation of the weight of the baby in the womb. 

3. Ultrasound Examination

Prenatal ultrasound evaluations provide reliable measurements, which are used to estimate approximate fetal weight for the gestational age. The common ultrasound measurements of fetus done during prenatal visits:

  • Head circumference
  • Bi-parietal diameter, distance between the sides of fetus's head.
  • Abdomen girth
  • Upper thigh bone

Nevertheless, even the best ultrasound measurements can not be as reliable as actually weighing and measuring a baby after birth.

When Fetal Development Is a Cause of Concern

Guarded outcome is feared if a low percentile position on fetal growth chart is accompanied by:

  • Compromised maternal health status: Attributable to chronic diseases in the mother or her lifestyle related toxins, which jeopardize optimal fetal development; tobacco smoking, coffee consumption or alcohol abuse.

  • Poor fetal growth noticed between two consecutive prenatal checkups.

  • Asymmetric growth recorded clinically and on ultrasound.

  • Non reassuring fetal testing (NST, BPP, CST).

  • Oligohydramnios - sub optimal volume of amniotic fluid.

  • Elevated umbilical artery (S/D) ratio:
    Doppler systolic/diastolic ratio greater than 3.0, after 30 gestational weeks, indicates an increased risk for low birth weight. This compares umbilical artery’s systolic with the diastolic flow of blood; and identifies the existing resistance to blood flow in the placental vascular system.

Causes of Large for Date Babies

  • Obesity in the mother
  • Diabetes in the mother - Gestational/Type 2 Diabetes
  • Post term baby
  • Multipara mother
  • Large size due to genetic, racial or ethnic disposition.
  • Previous pregnancy with a large baby

Common Causes of Small for Date Babies

The fetal growth chart is actually for the premature infants, but it also gives an approximate estimate of intrauterine growth of the unborn baby. They can also be used to monitor the percentile growth curve of developing fetuses. 

Wish to have one anyway? 
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Related pages of interest are indexed in the right column

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Fetal Growth Chart

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Causes of small for date baby

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