Inside the Womb: Who are the ''Players''?

by: Donna Tasco Poplawski, RN, C, MSN, WHNP

Pregnancy is an amazing phenomenon of nature that is the core of our existence. Yet even today, few people really have an understanding of what goes on inside a pregnant woman. It's not just nine months of belly growth followed by the birth of a baby. There is a partnership of "players" inside the mother's body that are the true "developers" of her baby. These partners -- the uterus, placenta, umbilical cord, and amniotic fluid -- are the key players which help the baby grow and develop until a time that is safe for him or her to be born.

The baby -- or "fetus" as it is known while still inside the mother -- is actually a parasite. The fetus physically cannot exist without the mother at this time and needs certain things from her to grow and develop to a stage that he can survive on his own. From his mother and through this partnership of players the fetus receives nutrients and oxygen, and eliminates his waste products through blood that is exchanged between himself and his mother. And it is the "players" who make this possible. Without them, there would be no vehicle for this crucial exchange between mother and fetus.

The uterus, when not pregnant, or gravid, is a pear shaped organ approximately the size of a fist. It has thick muscular walls that have the ability to stretch to several times its normal size along with the capability to house a fetus (or fetuses), a placenta (or placentas; see below), and a corresponding amount of amniotic fluid. It continues to stretch and change shape to accommodate its growing contents until the end of the pregnancy.

It begins the journey of pregnancy as a thick muscular structure resembling and upside-down pear. As it continues growing it changes to a rounder shape in the middle of the pregnancy, or ‘second trimester’. Moving into the "third trimester," or towards the end of the pregnancy, the uterus takes on a more oval shape and the walls are now very thin to better accommodate the growing fetus, placenta, and increase in amniotic fluid. This thinning of the walls also makes the muscle fibers stronger to more effectively push the baby out during labor and delivery.

Attached to the bottom of the uterus is the cervix. This is the neck-like part of the upside-down pear shaped structure that shrinks in length and dilates (opens) to allow the baby to pass from the uterus and into the birth canal (vagina) during birth. The uterus does the work and the cervix makes the changes during labor and delivery. All this activity causes the pain of labor.

By about six weeks after birth, the uterus, cervix, and vagina are back to their normal shape and size. However, they never quite go back to their original tight shape.

The placenta is amazing! It's my favorite player. Its function is fascinating as it is the link between mother and baby. This is where the exchange of nutrients, oxygen, and fetal waste products occurs. It has two sides: the maternal side, which is the side attached to the mother's uterine wall; and the fetal side, which is the side next to the fetus.

The maternal side is very dark red, spongy, and lobular (bumpy). It looks like a piece of raw liver. This is the busy side of the placenta where the exchange really takes place. This side has little finger like projections (villi) that imbed into the uterine wall so that the mother's blood and the fetus' blood can pass back and forth the necessary nutrients, oxygen, and fetal waste products that help maintain a healthy pregnancy.

The fetal side is smooth and shiny because a thin membrane called the amniotic membrane covers it. It has large blood vessels that start in the umbilical cord and fan out over the placenta. The amniotic membrane also functions as the amniotic sac. This is what encapsulates the fetus and amniotic fluid throughout the pregnancy. The membrane continues growing throughout the pregnancy to accommodate the enlarging fetus, placenta, and increasing amount of amniotic fluid.

Once the baby is delivered and the cord is cut, the placenta knows its job is done and usually within less than five minutes the placenta peels off from the uterine wall and is expelled through the vagina. Its life is over, even though the baby's is just beginning. It's an amazing process!

The amniotic fluid surrounds the fetus throughout the pregnancy. The fluid is produced from the amniotic membranes and from fetus' urine. Its function is to protect the baby from temperature changes, trauma and allow it the freedom to move about and stretch. It also keeps the uterine wall expanded so it won't compress the growing fetus and placenta. The fetus swallows, breaths, and digests the amniotic fluid. By the end of the pregnancy there is approximately 1000ml (1 liter) of fluid in the amniotic sac. The fluid is basically clear or a little cloudy in color and is continually being made. If a mother ruptures her membranes early in her pregnancy, the rupture site can seal over with bed rest and a doctor's help, allowing more fluid to accumulate.

The umbilical cord is the fetus' lifeline. This is the white spongy rope like cord that is attached at the umbilicus (belly button) of the fetus on one side, and to the placenta on the other. The cord itself has three blood vessels, two arteries and one vein (both protected by a white jelly substance called Wharton's Jelly). These are the vessels through which that the fetus sends her blood filled with waste products back to her mother and where she receives nutrients and oxygen from her mother.

The cord is approximately two feet long in length. The baby feels no pain when it is cut.

As you can now see, there are many things happening inside a mom's pregnant uterus. Pregnancy is a partnership of many players that help that fetus grow and flourish into a healthy newborn. If even one of the players were missing, the pregnancy could not develop. Excepting the uterus, all leave the womb with the baby, and all but the uterus are used only once. Their lives end just as the baby's begins.

Ms. Poplawski is a nationally certified obstetrical nurse with 20 years experience working with pregnant patients and their families. She is currently manager of Labor and Delivery at Morristown Memorial Hospital in Morristown NJ, a level III, high risk, regional perinatal referral center.

Ms. Poplawski received a BSN in 1980 from Seton Hall University, a master's degree in Nursing Administration 1995, and a post graduate certificate as a Women's Health Care Nurse Practitioner in 1998. She is also a nationally certified Perinatal Bereavement Counselor.

Copyright © Donna Tasco Poplawski. Permission to republish granted to Pregnancy.org, LLC.