Hormones & Pregnancy

Pregnancy is a complex physiological process that relies heavily on hormonal regulation to support both the developing foetus and the mother’s body. These hormones coordinate essential changes that allow implantation, growth, and preparation for birth. Understanding the key hormones involved and the body systems they affect helps explain many of the physical changes experienced throughout pregnancy.

hCG

Human Chorionic Gonadotropin (hCG), otherwise known as the pregnancy hormone, is the main indicator of pregnancy in pregnancy tests. hCG is mostly produced during the first trimester before levels decrease at the beginning of the second trimester. It is secreted by the placenta to encourage production of oestrogen and progesterone.

Estrogen

Estrogen is the hormone that is tracked when “trying” for a baby. As levels begin to rise, this indicates the fertile window! During pregnancy, estrogen continues to rise to ensure follicular and uterine lining growth. If estrogen levels are low, the follicle may not grow sufficiently to release the egg and the lining may not be developed enough for a fertilised egg to implant.

Progesterone

Progesterone’s role is to thicken and maintain the uterine lining. Secreted by a mass of cells called the corpus luteum, progesterone encourages the growth of blood vessels to supply the endometrium and help develop a fertilised egg into an embryo. Similar to estrogen, progesterone levels increase throughout pregnancy and peak at the third trimester. After childbirth, less progesterone is produced and fluctuates with menstrual cycles until menopause. 

Relaxin

Relaxin is produced during the first trimester to promote placenta growth and implanting the developing foetus into the uterine wall. Then when preparing for labour, relaxin is produced to “relax” ligaments in the pelvis and widen the cervix. 

Prolactin

To prepare for lactation, prolactin levels increase to stimulate the development of breast tissue and promote milk production.

Systems affected 

Gastrointestinal (GI)

• Morning sickness which presents as nausea and vomiting, is a common symptom of pregnancy. It occurs between 4-8 weeks of pregnancy but improves by 14-16 weeks. As smooth muscles within the GI tract relax, decreased motility can occur, leading to increased water absorption and constipation.

Musculoskeletal

• To accommodate the growth of the foetus, postural changes occur. Mothers may adopt compensatory postures to maintain their centre of gravity e.g leaning backwards. To allow for delivery, ligaments are predisposed to laxity which can lead to reduced joint stability. Joint or muscular pain, particularly in the pelvic region or lower back are common complaints during the later stages of pregnancy. 

Reproductive 

Uterus

• As the uterus increases in size throughout pregnancy, the uterus moves up from the pelvis into the abdominal cavity, which is followed by the abdominal organs being displaced. 

Cervix

• The cervix secretes a mucus to “plug” the uterus and prevent infections. Prior to delivering, the cervix softens and opens/dilates to allow the baby to be delivered.

Vagina

• During labour, the vagina’s muscle layer thickens and becomes more elastic to allow for dilation.

Overall, hormones play a vital role in maintaining a healthy pregnancy by regulating foetal development and preparing the mother’s body for childbirth. From early implantation to labour and postnatal changes, these hormones influence multiple body systems, resulting in both adaptive and sometimes challenging physical changes. Recognising these hormonal effects provides insight into the remarkable processes that support pregnancy and maternal health.

Kristen Ni

Senior Physiotherapist

Disclaimer: The information provided in this blog post is intended for informational purposes only and should not replace professional medical advice. Always consult with a qualified healthcare provider or physiotherapist regarding any specific health concerns or issues.