What causes a woman to go into labor when she is pregnant?

If we truly knew the answer to that question, we would be able to prevent a woman going into labor before her baby was fully developed.

What we do know is that hormones play a large role in keeping a woman pregnant and stimulating uterine contractions to begin labor.

As a pregnancy progresses the mother’s body produces hormones helping her stay pregnant until the baby can survive outside the womb. At the same time the hormones causing her to go into labor at the end of her baby’s gestation, gradually rise.

When ovulation occurs the ovaries produce progesterone. Progesterone prepares the uterus to welcome a fertilized ovum or egg. After around 8 to 10 weeks into a pregnancy the placenta takes over the production of progesterone. This maintains the perfect environment for a baby to grow and develop inside the mother’s womb, or uterus. One of the affects of this increased amount of progesterone on the mother is fatigue. Many mothers talk about how tired they are during the first trimester. Just before labor begins, women typically experience a sudden burst of energy. Is this because the progesterone levels have dropped suddenly? I think it also helps the woman have the energy she needs for labor.

Oxytocin is referred to as the “love hormone.” High levels of oxytocin are associated with love making, nurturing a baby, releasing of milk for a baby, and labor contractions. The elevated level of progesterone suppresses the production of oxytocin, keeping the mother from going into labor. Maybe this is also why some women are a bit irritable during pregnancy.

It may also explain why some women have what is called, premenstrual irritability. As a women nears her period the progesterone levels rise to prepare in case an egg is fertilized, which decreases her production of the “love hormone,” causing her to be a bit on edge. Gentlemen, all of this is real. We women are affected by our hormones.

Back to labor.

What stimulates this change in hormone productions? It could be the placenta is at the point of decreased viability and slows down in the production of progesterone. There is science supporting the theory that the baby releases surfactant, a substance secreted by the lungs of a fetus, causing a shift in hormones. Dr. Mendelson of the University of Texas Southwestern was able to prove in 2004 that they were able to identify: “a protein within lung surfactant that serves as a hormone of labor that signals to the mother’s uterus when the fetal lungs are sufficiently mature to withstand the critical transition to air breathing.”

Interestingly the mother’s body, as it nears labor, increases the production of the hormones called endorphins. Endorphins levels can alter the perception of pain and stress. They are also associated with a feeling of well being. The body naturally produces endorphins to help the woman cope with the pain and stress of labor.

Our bodies are amazing. If we ever do figure out what exactly causes labor to begin we will be able to prevent babies being born too early. Human mammals need at least 266 days to grow inside their mother to live well outside the womb. Thank goodness we aren’t elephants. They need 660 days.

This story was originally published September 18, 2017 at 5:01 PM with the headline "What causes a woman to go into labor when she is pregnant?."