This video follows on
from the previously covered content on physiological adaptations of pregnancy.
It focuses on the metabolic changes that occur.
If you understand these adaptations,
we are better able to understand
the changing nutritional requirements that are
necessary for optimal maternal and fetal health.
Metabolic adaptations involve coordinated changes
of carbohydrate and lipid metabolism that preserve
maternal homeostasis and allow timely transfer of nutrients
to the fetus in order to optimally support growth and development.
In the first half of pregnancy,
the physiological adaptations of maternal metabolism prepare the body for
the high demands of
rapid fetal growth which occurred then in the second half of pregnancy.
Therefore, we will begin by looking at changes
in carbohydrate and lipid metabolism that take place in early pregnancy
and then discuss how these metabolic pathways differ from changes
occurring in later pregnancy.
In early pregnancy, insulin-secreting pancreatic beta cells become hyperplastic,
resulting in increased insulin secretion.
Insulin sensitivity is enhanced and
the nutrient-stimulated insulin response to our glucose increases.
At the same time, glucose tolerance is either normal or slightly improved with
peripheral sensitivity to insulin or hepatic basal glucose production remaining the same.
Fasting plasma glucose level are slightly reduced with
only small changes in insulin levels during the first trimester of pregnancy.
Hence, the risk of hypoglycemia has increased in
some women during this early stage of pregnancy.
Changes in lipid metabolism are analogous to the alterations and carbohydrate metabolism.
During the first and second trimester, increased estrogen, progesterone,
and insulin concentrations favor lipid deposition and they inhibit lipolysis,
which results in an accumulation of maternal fat stores.
This accumulation peaks between 10 and 13 weeks of gestation before
the fetal demands for energy to support
extensive growth and last trimester increased significantly.
The maternal energy requirements are thus mainly
met by increased efficiency of glucose metabolism.
Being in an anabolic state, excess glucose,
as well as dietary triglycerides are stored as adipose tissue.
This maternal metabolic pattern changes during the second half of pregnancy.
Since glucose is the preferred fuel to the fetus,
a modest insulin resistance date develops.
This leads to a mild elevation of
maternal plasma glucose concentrations to facilitate diffusion across the placenta.
Despite increasing basal and postprandial plasma insulin levels,
the postprandial glucose concentrations are
significantly elevated and the glucose peak is prolonged.
The maternal insulin resistance begins to develop in the second trimester,
and it peaks in the third trimester.
It is generated by the release of
placental diabetogenic hormones such as human placental lactogen,
growth hormone, corticotropin-releasing hormone,
human chorionic somatomammotropin, and progesterone.
In late pregnancy, maternal metabolism shifts
from an anabolic to a catabolic state and it promotes
the use of lipids as a maternal energy source
while preserving glucose and amino acids for the fetus.
This shift allows pregnant women to minimize
protein catabolism and to preserve glucose as the main fuel for the fetus.
Decreasing lipid uptake into adipose tissue
to physiologically relative insulin resistance reduce
lipoprotein lipase and increased
lipolysis and mobilization of lipid stores results
in a constant increase in triacylglycerols,
non-esterified fatty acids, cholesterol,
phospholipase, and lipoprotein concentrations in blood plasma until delivery.