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Weight development

The weight of the embryo/fetus can only be estimated with the help of length sectional ultrasound measurements of various structures.

Fig. 6 - Weight course of the child during the pregnancy

Embryonic period
Fetal period

Fig. 6

The weight of the fetus experiences its largest increase in the third trimester. The variations, though, are quite large. This is emphasized with the scatter (light pink in the diagram).
At the end of the embryonic period, the embryo weighs only 3 g, at the end of the first trimesters around 90 g, and after the second trimester roughly 1200 g. The mean weight at birth amounts to around 3350 g.

Intrauterine, a large increase in weight takes place that depends, though, on genetic (mother/child) and environmental factors. At the end of the pregnancy the average weight amounts to 3350 g, but can vary considerably. At birth one distinguishes (mainly in English-speaking regions) among:

  • Low weight at birth: 1500 -2500 g
  • Very low weight at birth: 1000 -1500 g
  • Extremely low weight at birth: < 1000 g
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Graph a showing lengths of the embryo/fetus

This categorization says nothing about whether a child was born prematurely or was full-term. In most cases, the delayed intrauterine increase in weight results from deficient nourishment, whereby the fetus reacts most sensitively to maternal malnourishment in the last trimester.
Various hormones influence intrauterine growth. Initially they are mainly maternal hormones passing through the placenta, but later, in the fetal period, hormones produced by the fetus itself are also responsible for the weight increase.

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The following hormones are responsible for the intrauterine growth of the child:

  • Growth hormone (somatotropin), produced in the adenohypophysis, and insulin-like factors from the liver stimulate the growth and metabolism of cartilage, bones and muscles.·
  • Glucocorticoid (e.g. ACTH), produced in the adrenal cortex, accelerates fetal maturation.
  • Thyroid hormones (T3 and T4) released by the thyroid gland have an influence on fetal growth.
  • Insulin is an endocrine regulator of prenatal growth.
  • Local growth factors influence tissue growth and development.
  • Placental hormones have a large influence on the child's growth. The placenta produces factors that are partly protective and partly stimulating.

Prenatal growth thus depends on various elements. Sufficient and balanced maternal nourishment is the prerequisite for the normal thriving of a child. Further maternal factors are her size, her parity (i.e., how many children the woman she has already given birth to), diseases such as hypertonia, diabetes mellitus, etc., as well as her living conditions (smoking, drinking and/or other unhealthy habits).