The Hormonal Changes During Pregnancy No One Tells You About

It all starts with an egg breaking free from the ovary during ovulation. If that egg is fertilized with sperm, the fertilized egg begins differentiating into a group of cells called a trophoblast. This occurs about six days after ovulation. It is this trophoblast that produces the pregnancy detection hormone known as human chorionic gonadotropin (hCG). On average, hCG is detectable in your urine 10 days after ovulation/fertilization.

When your egg ruptured from the ovary, it left behind its outer coat called the corpus luteum. It is the job of hCG to maintain the corpus luteum1 so that the corpus luteum can make progesterone and estrogen to support embryonic growth. If your egg is not fertilized and you do not produce hCG, the corpus luteum slowly disintegrates and you will get your period. hCG is present throughout your whole pregnancy but reaches peak levels around week nine to ten; at this point the placenta is able to take over hormone production.

Estriol (E3) is the predominant form of estrogen during pregnancy. Cholesterol from your circulation enters the placenta and is required to make all steroid hormones. The production of estrogen2 depends on the mother and the fetus. You work together with your baby to make estrogen! Here's how it happens:

Phew!! Now that's teamwork! What does estrogen do?

What does progesterone do?

There are two thyroid hormones to take note of during pregnancy. T4 is an inactive, precursor hormone. T3 is your active thyroid hormone, which is derived from T4. Elevated estrogen levels promote elevated T3 and T4 to help with metabolism and regulation of steroid hormones.

Human placental lactogen2 is secreted by the placenta in order to help mom break down fats and carbohydrates for the baby. Unfortunately, this hormone opposes insulin so it can lead to insulin resistance in mom; this is why you may be screened for gestational diabetes at the end of the second trimester.

Cortisol is your "stress" hormone. As you near 40 weeks of pregnancy, cortisol production from the baby's adrenal glands increases. This increase makes the uterus more sensitive to contractions; it also increases estrogen in the circulation and decreases progesterone to allow for even more contractions! You may be familiar with Braxton Hicks contractions, which are false contractions that occur from pressure on the uterus, not from elevated estrogen.

Get ready to push! Oxytocin is made by mommy and is responsible for dilating the cervix and stimulating strong uterine contractions for delivering baby. After delivery, oxytocin is stimulated by the baby suckling on the nipple and promotes milk let down.

Hormones begin to normalize immediately after the delivery of the placenta, and are back to pre-pregnancy levels by day five post-labour. That's really quick! It is this spontaneous change in hormones that can lead to low mood in the postpartum period. Being more aware of the influence of these hormones on your body will help you understand what you're feeling and hopefully help you cope with the symptoms.