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