Understanding Pregnancy Hormone Changes

Understanding Pregnancy Hormone Changes

Hormones play a large part in pregnancy, childbirth and postpartum. They can make you bloated and moody; cause food cravings/aversions/heartburn and lead to other discomforts.

At first, progesterone and estrogen begin their work to thicken the uterine lining for egg implantation, followed by human chorionic gonadotropin or hCG which starts increasing every two days until reaching its peak around week 11.


Progesterone is essential in pregnancy as it both prepares the uterus lining to accept an egg for implantation and acts as a muscle relaxant to stop contractions until labor begins. Furthermore, progesterone balances out immune systems to enable their bodies to accept new DNA from a developing foetus.

Produced by the corpus luteum, which forms on one ovary after an egg has been released at ovulation and remains high during gestation until an implanted fertilized egg takes hold and then gradually decreases as placenta becomes primary producer.

Progesterone may cause side effects that are uncomfortable for women such as heavy bleeding between periods and vaginal discharge, and if its levels drop too low it could even lead to miscarriage. Doctors may prescribe it as birth control or to treat menstrual cycles that do not respond well to other treatments; its production takes place through double oxidation called 20a,22R-dihydroxycholesterol or pregnenolone; it has anti-inflammatory properties as well as normalizing blood clotting, vascular tone zinc/copper levels cell oxygenation/cellular oxygenation/use of fat stores as energy sources.


Hormones are chemical substances produced by one tissue that travel throughout the body via fluids to affect another tissue. Women experience fluctuating hormone levels throughout the day; during pregnancy however, those hormones take on additional roles to develop your baby.

Progesterone and estrogen, two hormones present during menstruation, increase to help prepare your uterus for conception. Once pregnant, HCG triggers another important pregnancy hormone: estradiol. This increases during the first trimester and remains elevated throughout your second trimester to assist your baby’s growth as well as increasing blood flow to your breasts, potentially increasing tenderness (1).

Late pregnancy sees your progesterone levels decline gradually, altering the ratio between estrogen and progesterone and its soothing effects, ultimately leading to irregular and weak contractions known as Braxton Hicks. Furthermore, prolactin reaches its highest concentration during this time and triggers your body into producing milk for your newborn.


HCG (human chorionic gonadotropin) is the pregnancy hormone detected by home pregnancy tests and doctor offices alike. Produced by what will eventually become the placenta, HCG signals to your body that there’s a baby growing inside and that it must prepare the uterus and shut off egg production at its monthly cycle.

Your hCG levels will quickly double during early pregnancy, believed to be responsible for the nausea and vomiting many women experience during the first trimester. Furthermore, HCG triggers progesterone which is essential in creating and maintaining thick uterine linings during gestation.

However, your hCG levels can also fluctuate frequently; according to OB-GYNs, it’s more important to focus on trends than individual numbers – since one high or low reading could still indicate an uncomplicated pregnancy.


Oxytocin is a naturally produced neuropeptide in the brain which works to induce contractions during labor and facilitate breastfeeding, while simultaneously playing an essential part in maternal behavior and maternal bonding. Oxytocin has also been linked to social bonding and emotional connections among individuals.

High levels of oxytocin, coupled with prostaglandins, promote the softening and dilation of the cervix during labor. They also cause the release of incretin hormones which help prevent postpartum haemorrhage.

Beta-endorphins, another hormone, control the release of oxytocin during labor by relieving pain and suppressing immune system activity. If too much stress builds up during labour, beta-endorphins could inhibit oxytocin and slow things down; staying calm is therefore essential to successful labour.

Once your baby has been born, oxytocin will linger around to help you relax and bond more tightly with him or her. It can also aid with breastfeeding by aiding with the let down reflex as well as guard against postpartum haemorrhage; which may explain why women who receive synthetic forms of oxytocin via intravenous drip have better birthing outcomes.


Prolactin, one of the five early pregnancy hormones known as “Fab Five”, promotes breast tissue growth and development for lactation purposes as well as hundreds of other physiological functions.

Prolactin levels rise during gestation in response to the baby suckling, prompting mammary glands in mother’s breasts to expand in preparation for breastfeeding after child birth. High levels of prolactin allow mothers to experience deep emotions of bonding and attachment as they care for their infants, along with oxytocin.

Hyperprolactinemia occurs when levels of prolactin exceed what is normal; this condition interferes with fertility by hindering ovulation in women and infrequent or irregular menstruation cycles, or lack thereof (oligomenorrhea), as well as producing sufficient amounts of the progesterone hormone post ovulation. In mild cases this may also impede production of enough progesterone post ovulation to maintain health fertility levels.

Excess prolactin levels in men can cause decreased gonadotropin secretion and testicular function, leading to decreased testosterone production resulting in symptoms like loss of sexual desire or dry vaginal discharge (galactorrhea). If there is an underlying thyroid disorder present, medications to address it may help lower prolactin levels as well.


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