Pregnancy causes many physical and chemical changes in the body of the mother to promote the development of a new baby. The hormone progesterone works with other hormones to synchronize events and interactions that are vital for the baby. As explained at Merck.com, progesterone is important before and during the pregnancy to synchronize events and functions of the body for the growth and development of a baby. This hormone helps prepare the womb (uterus) for implantation, maintains the pregnancy and helps stimulate the breasts for milk production after the baby is born.
Implantation
The hormone progesterone maintains the lining of the uterus, or endometrium, so that the fertilized egg can implant for pregnancy to occur. As explained by the University of Maryland Medical Center, high levels of progesterone are needed immediately after fertilization to maintain the endometrium. If progesterone levels drop, the endometrium is shed, as it does during menstruation. The fertilized egg can't implant and is also discarded. For this reason, problems with progesterone production can cause infertility or the inability to get pregnant.
Healthy Development
After the egg is fertilized, the corpus lutem (empty egg follicle in the ovary) is signaled by another hormone human chorionic gonatotropin to continue secreting progesterone until the placenta is developed a few weeks later. The placenta then secretes the large amounts of progesterone hormone that are needed to maintain the pregnancy. According to MayoClinic.com, progesterone levels are almost 10 times higher during pregnancy because this hormone is essential for the growth of blood vessels in the walls of the uterus as the baby grows. If the placenta isn't able to produce progesterone, the endometrium lining won't develop normally to support that growing baby, causing bleeding, abnormal growth or a miscarriage.
Birth Timing
Progesterone also prevents the uterus from contracting early, causing premature labor and birth. Preterm birth is considered to be delivery earlier than 37 weeks of gestation in the uterus. Research from the Yale School of Medicine suggests that premature birth is often caused by the weakening of the membranes, the chorion and amnion, that form around the fetus and amniotic cavity. The study showed that progesterone was responsible for preventing apoptosis or cell death in these fetal membranes, keeping them from weakening or breaking.
Nourishing the Baby
Other body systems such as blood circulation and respiration in the pregnant mother undergo changes so that the developing fetus can be nourished properly for a healthy pregnancy, as listed by Merck. A high level of progesterone is needed to signal the brain to lower carbon dioxide in the blood. This causes women to breathe deeper and faster during pregnancy so that adequate amounts of oxygen is delivered to the fetus and carbon dioxide is cleared faster. Progesterone also helps to ensure that the breasts are able to produce milk after the birth.
