Physiologic Third Stage

Midwifery Today, Issue 133, Spring 2020.
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“Physiologic” third stage of labor means that this stage happens on its own—with no interference or treatment whatever—and is within the bounds of normal functioning.

The third stage of labor begins after the baby is born and ends when the placenta separates from the wall of the uterus and is passed through the vagina. This stage is often called delivery of the “afterbirth” and is the shortest stage of labor. It may last from a few minutes to 20 minutes (WebMD 2017).

This definition is standard, but somewhat problematic. The most serious complication of third stagehemorrhage—can start at any point. Often it starts after the placenta is delivered, when by definition the third stage is over. It can be as severe as or worse than hemorrhage before placental delivery. Further, physiologic third stage can last longer than 20 minutes without any abnormality. If the placenta has separated normally and descended into the vagina, and there is no abnormal bleeding, placental delivery can safely take its time.

Physiology and physiologic have different meanings. Physiology is a branch of biology that deals with the functions and activities of living matter (such as organs, tissues, or cells) and the physical and chemical phenomena involved. The physiology of the placenta is complex and elegant.

Physiologic refers to something that is normal and not due to anything pathologic or significant in terms of causing illness; i.e., physiologic jaundice is jaundice that is within normal limits. Physiologic and physiological have essentially the same meaning.

The placenta is a maternal-fetal organ. The circulations of both mother and baby flow in and out of the placenta and do not mix.

The fetal vessels in a normally implanted placenta do not pass into the basal layer. The basal plate, which is the upper margin of the maternal side of the placenta, is sometimes called “the zone of cleavage.”

At full-term pregnancy, the uterus, baby, and placenta have grown together since the start, when the embryo penetrated into the endometrium and began its development. The maternal arterioles and venules grow out beyond the basal layer and make their connection with the fetal circulation; they pour their blood into “maternal lakes,” which are like the open areas in a sponge. Tiny fetal vessels from the umbilical cord dip into the maternal lakes, where they absorb nutrients and pass off metabolites for the growing and developing baby. The maternal blood in the lakes flows back through the uterine veins to the heart and lungs again.

The placenta acts as the baby’s lungs, kidneys, and more. The blood of the mother and the blood of the baby are separated by the walls of the fetal arterioles and venules in the maternal lakes; substances the baby needs, or needs to excrete, diffuse across the vessel walls. A pint of blood a minute passes through the maternal placental circulation at full term.

When the baby’s circulation does penetrate into the basal layer, it is called placenta accreta—a serious complication in which the placenta grows into the wall of the uterus. The placenta does not separate normally and hemorrhage occurs. Many maternal deaths are caused by placenta accreta.

When the baby is born, the uterus contracts—shortening and drawing together muscle fibers that run both horizontally and vertically. The fibers tighten around the maternal vessels and constrict them. The placenta sheers off at the zone of cleavage and blood loss is stopped by constriction of the vessels. The blood clotting system comes into play. A clot forms at the area where the placenta was attached. Usually the placenta drops into the vagina.

The time of birth is a holy time. The newly born person has emerged to take his or her place among us. The mother/baby duo is in transition. Baby is ideally in mother’s arms, snuggling skin to skin. Often they have locked eyes in the age-old communion of love and wonder. They are bonding and should not be separated for any trivial reason.

Hormonal changes promote bonding and also physiologic third stage. The high adrenaline levels of birth fall; oxytocin (the hormone of love) increases. Endorphins are at high levels, promoting attachment.

Increasing oxytocin levels contract the criss-cross uterine fibers to act as living ligatures around the blood vessels in the place where the placenta was attached, preventing excessive bleeding. Clotting factors continue to be released—decreasing blood flow.

The umbilical cord has been the baby’s lifeline for months. The fetal circulation remains open to the placenta and will capably pump a small transfusion of the baby’s blood into its body if the cord is not cut. There are few if any reasons for early cutting of the cord. It has been a mindless procedure for years now … probably 150 years or more. It amuses me that major studies have been done comparing immediate and delayed cord cutting, using the definition of delayed cord cutting as three minutes after birth. To me, three minutes after birth constitutes early cord cutting! Anyway, the studies find that it’s better for baby if the cord remains intact—at least for three minutes. Considerable benefits are found even with this short delay.

Early and prolonged contact between mother and baby promotes breastfeeding. Breastfeeding promotes production of oxytocin, which assists in contraction of the uterine muscles in a physiologic way. Discussion of its innumerable benefits to mother and baby go beyond this message. Nevertheless, mothers’ choices must be accepted. Mother-led childbirth can often help a midwife or birth attendant find the best way.

Keep baby and mama together in these early hours. The bonding time is unique. It is not the time to pass the baby around to family. Mother-baby bonds can be tenuous right after birth, especially for the youngest moms and women undergoing trauma. Give these women a chance to find their way with the baby. Need a blood sugar test? Do it at the bedside. If mom needs to get up to go to the bathroom, that is the time for baby to be held by a family member or support person.

Third and fourth stage are the most common times in pregnancy for hemorrhaging, and hemorrhage is the most common cause of maternal death in the world, even, in recent years, in the United States (WHO 2019).

For this reason, active management of the third stage (AMTSL) was developed. It consists of giving an anti-hemorrhagic that promotes uterine contractions with or just after the birth, early cord cutting, and delivery of the placenta with controlled cord traction(WHO 2012).

However, some research has shown that while—for women in general—active management of third stage decreases blood loss, for a subgroup of women it increases it. These are the women who have had physiologic labor (Buckley 2020).

It seems that when first and second stages of labor have been physiologic, the body is primed to deliver the placenta without problems. Once the labor ceases to be physiologic, consider active management of the third stage.

I have seen skilled midwives move seamlessly to combine elements of physiologic and actively managed third stage according to the needs of the woman they are with. Knowledge of the physiology of third stage can allow them to pick and choose the elements needed for any one woman.

In Uganda, East Africa, where I have done medical volunteer work for years, the midwives at Teso Safe Motherhood practice active management of labor as advised by WHO. They give an anti-hemorrhagic, make sure the placenta has detached and is moving into the vagina, then settle into watchful waiting for placental delivery to complete.

A working knowledge of the physiology of third stage allows a midwife to practice expectant management and then—if needed—step in to get the placenta delivered and stop bleeding, using active management procedures and skills. Supporting the physiologic process of childbirth even when complications arise brings the best results.


About Author: Marion Toepke McLean

Marion Toepke McLean, CNM, attended her first birth as primary midwife in August 1971. She received her nursing degree from Pacific Lutheran University in 1966 and her midwifery and family nurse practitioner degree from Frontier Nursing Service in 1974. From 1976 through 2001 she did home, clinic and hospital births, while also working as a family nurse practitioner. In 1980 she taught a year-long program for local midwives, returning to Frontier Nursing Service to teach during the summer. She had a homebirth practice until 1985, when she went to work at the Nurse-Midwifery Birthing Service, a freestanding birth center. In June 2000 she completed a BA in International Studies at the University of Oregon, with concentrated studies on Mexico. Since 2002 she has worked in a reproductive health clinic and attended an occasional homebirth. She lives in Eugene, Oregon, and is a contributing editor to Midwifery Today.

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