 Hormone Levels During
Pregnancy
Author
Paul
Kenyon
For
obvious reasons,
most of our knowledge about the biological bases of maternal behaviour
has come from studies of animals. For example, it would be unethical to
artificially manipulate hormone levels in women in order to investigate
the role of hormones in their behaviour. Nevertheless it is possible
that the principles governing such an important behaviour that emerge
from studies of animals may be echoed in the behaviour of our own
species.
The
observation that blood transfusions from maternal rats induced maternal
behaviour in nonpregnant females, suggested that hormones may play an
important role in switching on (initiating) maternal
behavior. The diagrams on this page illustrate the dramatic changes in
hormone
levels around parturition in rats. Similar changes occur during human
pregnancy.
Notice
that:
- progesterone
declines during the last days of pregnancy
- estrogen
increases just before birth
- prolactin
increases just before birth
- the
'Separator Tool' allows
you to see the levels
'one-hormone-at-a-time'
- the
'Overlayer Tool'
allows you to build up a picture of changes
in all three hormones during pregnancy
Is
this cluster of hormonal changes responsible for switching on maternal
behavior ? It is difficult to study the role of hormones in natural
pregnancy because if you inject or remove hormones during pregnancy
there are multiple effects on lactation and behavior that are difficult
to disentangle. Jay Rosenblatt examined
the hypothesis that the decline
in progesterone level seen towards the end of pregnancy
triggers the onset of maternal
behaviour.
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