Understanding Pregnancy Hormones

Your body produces many hormones during pregnancy to cause all the necessary changes for growing and nurturing a baby. These hormones play a major role in every stage of pregnancy, from conception through postpartum. You can also blame many of the annoyances and discomforts you experience during these nine months on pregnancy hormones.


Progesterone prepares the uterine lining so it becomes thicker and easier for a fertilized egg to implant. It also slows things down in the digestive tract, which may cause heartburn, indigestion or constipation. One of progesterone’s most important functions is relaxing muscles. In particular, it allows the uterus and pelvis to stretch and open for pregnancy and birth. During the first 10 weeks, a part of the ovaries called the corpus luteum produces the progesterone while the placenta is forming. Once the placenta is fully developed, it takes over production. Progesterone levels rise very quickly during the first trimester, but then level off.


Estrogen is also produced by the corpus luteum until the placenta is completely formed. Your body has about 100 times more of this hormone during pregnancy than it does during a menstrual cycle. Several stages of fetal development are set in motion by estrogen, such as the growth and functioning of the baby’s adrenal gland. It also keeps the placenta and uterus healthy. On the downside, increased estrogen can cause nausea, hunger, skin problems and headaches. You will mostly likely experience increased vaginal discharge as well.

Human Chorionic Gonadotropin (hCG)

HCG may be the most important pregnancy hormone. It’s the reason you get a positive on a home pregnancy test or a blood test (hCG is excreted in urine). This hormone begins production after implantation and doubles roughly every other day during the first few months of pregnancy, peaking around 10 weeks. HCG keeps the pregnancy healthy and tells the body to prepare for a baby. Unfortunately, it is also to blame for several unpleasant pregnancy symptoms, including morning sickness, heartburn, and dizziness.


Relaxin is a hormone that causes your ligaments and joints to loosen. Its main purpose is preparing your body for childbirth, but it can also lead to some aches and pains as it affects parts of your body besides the uterus and pelvis. Your body has 10 times more relaxin during pregnancy, so you will most likely feel a difference.


Labor is started when the body responds to oxytocin. This is the hormone that causes your cervix to open and your uterus to contract, including after delivery when your uterus needs to contract to return to its normal size. Oxytocin is also responsible for signaling your nipples to let down milk when you breastfeed. Many people consider oxytocin to be a bonding hormone that helps you feel happy and close to your baby after delivery as well.


Prolactin levels can rise up to 20 times during pregnancy and may cause your breasts to become sore or te