Stress is defined as a a breakdown in equilibrium that is due to life events. All the environmental events that modify the milieu interne that is characteristic of the living beings are classified as stressful events. This concept undergoes constant modification and is absolutely not static.
It is now agreed that fetal grown results from two development influences: expression of genetic inheritance (innate), and epigenetic and environmental factors (acquired). In the setting of neurobiology, the very early acquisition, between 8 and 10 weeks of gestational age, of receptors for the main functions of perception, which constituites the passage from the embryonic to the fetal period, gives a good idea of the importance of these epigenetic or environmental factors in, for example, the quality of cerebral growth.
It can thus be considered that stress, an environmental factor, can play a role in the course of these two processes, either by its direct effect on the growth or differentiation of an organ or function, or, more often, by a mixed effect.
Considering the four periods of prenatal life and growth, stress could alter the mother-fetus relationship and embryo-fetal growth at the time of creation, conception, the embryonic phase, or the fetal phase.
TIME OF CREATION
For psychoanalysts and psychiatrists, this is the time when a man and women, who are in love, have the desire of creation, of have a baby. At this period two different categories of stress are possible: from the immediate environment, often but not always conscious, and from this trangenerational heritage, which is dominated by the unconscious.
The conseguences of these stresses are umpredictable. Most obvious is the impossibility of becoming pregnant, leading to the diagnosis of "sterility", which, very often, is only "hypofertility" which could be treated and cured by psychotherapy or other advice.
TIME OF CONCEPTION AND IMPLANTATION
This is the time of the union of the ovule and the spermatozoon in the fallopian tube. In the five post ovulatory days there is an action on the ovule by the secretion of specific proteins with long chains and high molecular weight, different for each postovulatory day and active at the time of implantation; on the spermatozoon by preservation of spemobiles, and on the fertilized ovule by active role in division and growth and activation of genoma.
It is now possible to demostrate the presence on the surface of the oula of the receptors for specific proteins like IGF1 and IGF2. The distribution of the receptors varies according to the time of ovulation-conception and implantation in the uterine mucosa. Many scientists accept the idea that this distribution is a function of the mother's psychoaffective quality. This means that psychological stresses in the mother could act on the action of IGF2, which is responsible for the placenta development.
THE EMBRYONIC PERIOD
This period starts at the time of implantation in the uterine mucosa until the 8th week after ovulation. Embryonic growth is fantastic, since in 8 weeks or 56 days the embryo goes from one cell (fertilized ovule) to more 8 billion cells. Mainly under genetic influence, this cell explosion is sensitive to the environment throught the placenta that means under control of IGF2. In this period, a good psychological attitude by the mother is important in the prevention of intrauterine growth retardation, mental handicaps and prematurity.
THE FETAL PERIOD
It is during the time of pregnancy that we have the most experimental and clinical data about the conseguences of maternal stress an the behavior and the neonatal brain.
In a series of experiments there are evicdence that laboratory sign of fetal asphixia never occurred at the time of surgical placenment of the fetal catheters when the mother monkey is anesthetized. On the other hand, the signs of fetal asphixya always occurred when the monkey awoke. The scientists therefore consider that the fetal asphixya was not due to the surgical procedure or mechanical aggression, but instead to the maternal stress.
The dermatoglyphic abnormalities and the occurrence of schizophrenia resulting from maternal stress during the second trimester have been demonstrated in many scientific studies.
The second trimester of pregnancy in humans is an important period for the massive migration of neurons to the cerebral cortex. In the same period, the dermal cells of the papillae of the fingers migrate to form the dermatoglyphics. In the macaque monkey, following maternal psychosocial stress, the newborns had dermatoglyphic asymmetry between right and left hands. Major dermatoglyphic asymmetry between left and right hands was always associated with greater perinatal mortality.
There are evidence also of the persistence of behavioral abnormalities long after birth in humans. Many scientific studies showed that adults whose fathers died before their birth commit more criminal acts and have more severe psychiatric problems than those whose fathers died in the year following their birth. Probabily certain traumas became very important because occur between the third and fifth month of pregnancy, during the development of the Thalamus, which is believed to be an early center of emotion.
On the other hand, the protective role of the mother has been well demonstrated by pregancies that occurred under dramatic conditions in the Second World War as well as in cases of subacute stress where the mother gave birth to a normal term infant.
There are many imprints that can affect the fate of the individual; they may arise from the socioeducational environment, fron emotional experience, from parental messages of permission or prohibition that affect behavioral activity, or, indeed, from the genomic imprit and early environmental effects that will have repercussions an the development and morbidity of the adult.
There are critical periods during fetal development that correspond to phases of growth and functional differentation, during which structures and functions are estabilished. Thus, various kinds of influence, exspecially nutritional, can affect the development of certain tissue or sistems whose repercussions will be felt only later, during adult life.
Some epidemiological studies, carried out with the necessary rigor, seem to prove that Hypertension, lipid disorders, non-insulin-dependent diabetes mellitus and hyperfibrinogenemia, i.e. the classical signs of coronary artery disease, are programmed during fetal life and are the late conseguence of a pathological early environment reflected in intrauterine growth retardation and low weight at birth and at 1 year.