Food and the Fetus 
Pregnant women are now being advised to gain more weight than was previously 
recommended in order to insure survival of the fetus and the newborn infant 
by Myron Winick 
Over the past few years, one of med- 
icine’s fundamental beliefs about 
pregnancy and the development of the 
human fetus has been challenged. Un- 
til recently the fetus was viewed as 
a parasite capable of extracting the 
nutrients it needed from the vast stores 
contained within the mother’s body. 
For this reason nutrition during preg- 
nancy was not considered very im- 
portant for the average mother, and 
weight gain was kept to a minimum 
with the rationale that this would pro- 
tect the mother from future obesity 
and in no way affect the growth and 
development of the fetus. We know 
today that neither of these statements 
is true. Weight restriction during preg- 
nancy will not protect the mother from 
future obesity and the fetus will not 
grow properly if the mother’s weight 
gain is insufficient. To understand why 
this is true, it is necessary to examine 
some of the physiological adjustments 
that a woman’s body makes during 
pregnancy and the way in which these 
adjustments.are affected by nutrition. 
Early in pregnancy the uterus be- 
gins to grow in order to accommodate 
the developing fetus. In addition, the 
blood flow to the uterus increases 
markedly since much more blood will 
be necessary to supply the nutrients 
and remove the waste products passing 
to and from the fetus through the 
placenta. For this increase in available 
blood to take place without interfering 
with the mother’s own needs, her total 
blood volume must also increase. Thus 
early pregnancy is characterized by 
a series of changes that include an 
increase in maternal blood volume, an 
increase in uterine blood flow, and 
the development of the placenta with 
its rich blood supply. Recent studies 
have shown that inadequate nutrition 
affects all these processes, reducing 
the increase in maternal blood volume 
and both uterine and placental blood 
flow. If the mother is undernourished 
early in pregnancy, the “lifeline” to 
the fetus will be inadequate and nu- 
trients will not be efficiently trans- 
ported to the fetus. 
As pregnancy proceeds, the mother 
undergoes further adaptation to insure 
proper fetal nutrition after birth. The 
breasts, which will become the organ 
capable of producing the infant’s total 
food supply, begin to grow and to de- 
velop the capacity to synthesize milk. 
In addition, fat is carefully laid down 
in deep sites within the body to store 
the energy necessary for lactation. The 
mother will expend more energy dur- 
ing the period of lactation than at 
any other time of her life, and her 
body begins to prepare for this effort 
during pregnancy. In fact, the prep- 
arations for lactation are so important 
that if the mother is inadequately 
nourished, they will take place even 
at the expense of fetal growth. The 
logic of this system is more easily un- 
derstood when we remember that until 
the advent of infant formulas before 
the turn of the century, no infant could 
survive without successful breast feed- 
ing. Thus, infant growth is less of a 
priority than adequate preparation for 
lactation, and a mother who is inad- 
equately nourished will continue to de- 
posit fat even though fetal growth is 
slowed. 
For the fetus to grow properly, the 
mother’s metabolism must adapt not 
only in early pregnancy so that enough 
maternal blood will circulate through 
the placenta but also in middle and 
late pregnancy so that enough fat will 
be deposited to insure an adequate 
ability to lactate. To accomplish this 
second goal, another series of adaptive 
changes usually takes place. In par- 
ticular, the mother’s appetite increases 
and she begins to consume more food. 
Moreover, certain changes occur in 
her gastrointestinal tract, resulting in 
the more efficient absorption of a 
number of specific nutrients, including 
iron and calcium. (As we shall see, 
the fetus needs these substances in 
particularly large amounts.) 
When food is abundant these adap- 
tive changes work extremely well. 
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