Physiology of Pregnancy: Role of Hormones in Maintaining Healthy Pregnancy

Running head: PHYSIOLOGY
Physiology
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Introduction:
Pregnancy is associated with many physiological changes in a woman’s body and these
changes promotes healthy development of the fetus. Pregnancy related physiological changes
initiate after conception and affect every organ systems. Pregnant women are more likely to
experience symptoms of nausea and vomiting, which are adaptive mechanisms during
pregnancy, to prevent women from consuming teratogenic substances. Such etiology of
pregnancy is also linked to many pregnancy associated hormones such as human chorionic
gonadotropin (hCG) hormone and oestrogen (Soma-Pillay et al. 2016). The main purpose of this
report is to discuss the role of hormones during pregnancy and provide a detailed insight into the
function of different hormones during different stages of pregnancy.
Endocrinology of pregnancy:
The endocrinology of human pregnancy is an important factor that helps to maintain a
healthy pregnancy. The endocrine changes occur because of physiological alterations in the feto-
placental unit (FPU). The FPU is the boundary site between fetus and mother and it is the site
where hormonal production and secretion takes places. Hormonal signals originating from FPU
during pregnancy are linked to endocrine and metabolic changes in pregnant women. Both
neuronal and hormonal factors maintain the pregnancy and its associated changes. Proper timing
between neuro-endocrine events facilitates fetal growth. Progesterone, estrogen and hCG are
some key hormones involved during pregnancy and the function and role of each hormone in

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pregnancy physiology is explained in detail in the next section (Bazer 2012).
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Figure 1: FPU, the boundary between fetus and mother and a major site for protein and steroid
hormone production and secretion. Source: (Bazer 2012).
Pregnancy associated hormones and their role in different stages of pregnancy:
Progesterone:
Steroid hormones like progesterone is produced extensively during pregnancy. For
instance, the synthesis and secretion of progesterone from corpus luteum initiates from the fourth
week of gestation until the placenta grows up by eighth week to actively synthesize the hormone.
About 250mg/day of progesterone is produced from placenta during pregnancy. Placenta
synthesizes progesterone from cholesterol by forming pregnenolone followed by its
hydroxylation to produce the hormone (Kumar and Magon, 2012). Hence, placenta is the unit
where progesterone is produced and secreted.
Progesterone plays a crucial role in each stage of pregnancy. It plays a role in the process
of reproduction by inducing changes in the lining of uterus and promoting successful
implantation of the embryo. During early pregnancy, it induce immune response in the mother’s

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body to prevent rejection of the embryo. In the first trimester, it is mainly involved in
maintaining health and development of fetus by thickening the uterine lining and maintaining
optimal function of the placenta. It also prevents contraction of the uterus allowing the baby to
expand in the womb (Dante,Vaccaro and Facchinetti 2013). In the second and third trimester of
pregnancy, progesterone also reduces the risk of preterm birth. The secretion of progesterone
increases in the second semester and by the last trimester, the volume of progesterone increases
from 340 to 675 nmol/L (Edelstam et al 2007). Hence, it can be concluded progesterone
hormones supports the endometrium to provide conducive environment for the survival of the
fetus. The binding of progestin to the progesterone receptor help in maintaining pregnancy
(Soma-Pillay et al. 2016).