What is a Birth Canal?

The muscular canal connects the uterus to the rest of the body. The baby passes through the birth canal during delivery which is also often known as a vaginal canal or born canal. The uterus, ovaries, fallopian tubes, cervix, and vagina are all the parts that contribute to the birth canal and are the primary organs of the female reproductive system. The act of bringing a child forth from the uterus, or womb, through the birth canal is known as birth, also known as childbirth or parturition. The mechanism and sequence of changes that occur in a woman's organs and tissues as a result of the growing foetus are constantly evolving. The gestation period of the labour has three important stages: the dilation stage,  expulsion stage and placental stage. It is in the second stage which is the expulsion where there are various fetal presentations and passage through the birth canal. And in this article, we will discuss all the possible fetal head positions in the birth canal once the stage of expulsion terminates.


Different Fetal Presentation and Passage Through the Birth Canal 

The location of the foetus and the form of the mother's pelvis determine how the child moves through the birth canal during the second stage of labour. When the mother's pelvis is of the normal form the following sequence is more common wherein the child is lying with the top of its head lowermost and transversely positioned and the back of its head (occiput) oriented toward the left side of the mother. As a result, the top of the head is in front, and its long axis is transverse.


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Entry of the Fetal Head Into the Birth Canal 

The pressure exerted on the child's buttocks by uterine contractions and bearing-down efforts is transmitted along the vertebral column, driving the head into and through the pelvis. Because the spine is attached to the base of the skull, the rear of the head progresses faster than the brow, causing the head to flex until the chin comes to rest and lie against the breastbone. As a result of this flexing mechanism, the top of the head becomes the leading pole, and the ovoid head circumference that entered the birth canal is replaced by a smaller, virtually round circumference with a long diameter of about 2 cm (0.75 inches) smaller than the previous circumference. 

As the head moves farther into the delivery canal, the birth canal becomes more narrow. The bony pelvis and the sling-like pelvic floor, or diaphragm, which slopes downward, forward, and inward, provide resistance. When the back of the child's head, which is the child's leading section, is driven against the slanting wall on the left side, it is naturally pushed forward and to the right, as it moves forward. This internal rotation of the head aligns its largest diameter with the largest diameter of the pelvic outflow, substantially aiding the adaptation of the advancing head to the shape of the cavity through which it must pass. As soon as the head is delivered, the neck, which was twisted during internal rotation, untwists. As a result, the top of the head is tilted to the left and backwards almost soon after birth.


Baby Rotation During Birth in the Birth Canal

With a curled spine, head down, and arms and legs are drawn tight to the body, the foetal position resembles a C-shape. While the kid will stretch, kick, and move around a lot in the womb, here is usually where they will spend most of their time. The most pleasant posture for a newborn in the womb and after delivery is the foetal position. This position becomes more crucial as the due date approaches because it helps the baby move into the ideal position for birth and reduces the risk of difficulties during delivery. The foetal position in the uterus usually indicates the baby is hanging upside down. Babies have an uncanny ability to sense when the delivery is approaching. Most newborns are able to arrange themselves into a head-down position by 36 weeks, allowing them to escape as quickly as possible. Others determine that they are perfectly content and have no intention of leaving.


Fetal Head Positions and Movements of the Birth Canal


Fetal Head Positions

Movements Within the Birth Canal

Occiput Anterior (OA)

  • Also called vertex position and cephalic position

  • This is the ideal position where the baby can easily exit the birth canal. 

  • The feet are up. 

  • head down facing your back, 

  • with their back resting against your belly. 

  • with the back of their head, closest to your pubic bone this means that they can exit the birth canal. 

Occiput Posterior (OP)

This posture is similar to the optimal upside-down foetal position for birth, however, the baby is facing the mother’s belly instead of the back. The back-to-back position is also known as the sunny-side-up position. The baby can't tuck their chin down to help them pass through the delivery canal more easily in the OP position. Labour may take longer if the baby is in this position and unable to turn over. In this case, due to an unideal position of the fetal head, the doctor usually recommends C-section as normal delivery involves risk in occiput posterior fetal presentation. 

Breech Position

About 3% to 4% of full-term newborns choose to be born with their heads up and their bottoms down in the breech position. There are several types of breech positions, each of which increases the likelihood of caesarean delivery. 

  • Complete breech position- The baby's bottom is toward the birth canal, their knees are bent close to their chest, and their feet are near their bottom.

  • Frank breech position- The baby is in the shape of a V, with the bottom near the birth canal, the legs up, and the feet near the head.

  • Footling breech position- When a baby is born with one or both legs close or in the delivery canal, it is known as footling breech.

Oblique Position

Because the head isn't properly aligned with the delivery canal, this posture is more dangerous during birth, as it might induce umbilical cord compression. If the umbilical cord enters the birth canal first, pressure from the head during delivery might compress it, restricting blood flow and resulting in a medical emergency. Oblique refers to the baby's posture in the womb, which is diagonal. The chances of occurrence of this position are slim but not impossible and whenever it occurs the caesarean is the only way.

Transverse position

The baby may be curled up in the foetal position in the transverse position, but they are laying sideways across the womb. The Baby's back, shoulder, or hands and feet may be the ones closest to the birth canal. The greatest danger of this position is that the placenta may be destroyed during delivery or when the infant is turned. The doctor will determine whether a C-section is the best option or not.


Your doctor will check on your baby's location in the womb in the weeks and days running up to your due date. Your doctor may employ a few strategies to gently move your baby into the ideal position for birth if it hasn't already done so. External cephalic version (ECV) is the medical term for the procedure of coaxing a baby into place inside the womb- because the coaxing comes largely from the outside of the stomach, it's called external. Turning the baby cephalic actually means turning it into the head-down position by gently massaging it. And Version in ECV is just another term for turning the baby.


ECV is Only Done When These Following Conditions Hold- 

  • When there is only one baby in the womb and not in the case of twins, triplets or more.

  • If one is scheduled for delivery in the hospital ECV can be applied because in an emergency case they can be immediately sent for C-section. 

  • When the mother is between 36 and 42 weeks along.

  • Labor has not yet begun.

  • The water hasn't broken yet, but one is in labour.

  • When the baby is surrounded by a large amount of amniotic fluid.

  • When the infant isn't contacting the birth canal's opening and no part of their body is in the birth canal.

  • Stomach muscles are understandably less tight when one has previously had a baby and in the case of a first-time mother, ECV will not probably be successful or will be a delayed process due to the tight muscles. 


During the External Cephalic Version Procedure Following Steps are Followed-

  1. To locate the exact location of the fetal head a fetal ultrasound is done and then the nudging process to shift the position if not ideal starts.

  2. An injection is given that relaxes the womb.

  3. The doctor massages by pressing on the stomach using both hands for an evenness.

  4. To keep you comfortable, one may be given a numbing (epidural) medicine.

  5. The vital signs, such as heart rate and blood pressure, are thoroughly monitored.

  6. To make it easier for your baby to move, your doctor will make sure there is enough fluid around them.

  7. During the procedure, the provider will employ baby heart monitoring to ensure that your baby's heart rate is normal.


Birth Canal Issues 

The following issues can delay the delivery of the baby and that can lead to damaging consequences.

  • Failure to progress- The fetal head does not move ahead that prolongs the delivery which can be fatal. When this happens in the later active stages during pregnancy it is mostly due to cervical dilations that are sluggish, caused by emotional issues such as worry, stress, and fear of sluggish effacement of a huge baby, a small birth canal or pelvis delivery of multiple babies. 

  • Fetal distress- this occurs when oxygen levels are insufficient, an anaemic condition in the mother, hypertension in the mother as a result of pregnancy, intrauterine growth retardation (IGR) is a condition in which a baby (IUGR) and Amniotic fluid with a meconium stain. 

  • Perinatal asphyxia - “Failure to initiate and sustain breathing at birth” is what perinatal asphyxia is characterised as. It can happen before, during, or right after delivery as a result of a lack of oxygen. It's an amorphous term. A reliable source that deals with a wide range of issues. It leads to hypoxemia, or low oxygen levels, high levels of carbon dioxide and acidosis, or too much acid in the blood. 

  • Shoulder dystocia- When the head is delivered vaginally but the shoulders stay inside the mother, this is known as shoulder dystocia. It is uncommon, but it is more common in women who have never given birth before, accounting for half of all caesarean deliveries in this category.

  • Excessive bleeding- During the pain in the pelvic or back when accompanied by bleeding the birth canal is at a risk. 

  • Malposition- This occurs when the baby's neck is hyperextended in this face presentation. The baby's bottom is first in a breech presentation. The infant is curled against the mother's pelvis in a shoulder presentation. All the aforementioned reasons can be called the malposition of the fetus and the birth canal becomes incapable of delivering normally and surgery needs to be performed even after the baby does not return to a normal position after ECV.

  • Placenta previa- When a baby's placenta partially or completely covers the mother's cervix — the uterus's outflow is known as placenta previa. During pregnancy and delivery, placenta previa can cause serious bleeding. One may bleed throughout pregnancy and during delivery if you have placenta previa which can put the mother’s life in extreme danger. 

  • Cephalopelvic disproportion- Cephalopelvic disproportion (CPD) is a pregnancy problem in which the mother's pelvis and the baby’s head are not the same sizes. The baby's head is proportionately too large, or the mother's pelvis is too tiny, for the infant to pass through the pelvic opening comfortably.


Other Ways to Induce Labor 

  • Get moving. Movement may help start labour.

  • Having Sex is often recommended for getting labour started.

  • Try to relax in any way that suits the mother. 

  • Having something spicy. 

  • Scheduling an acupuncture session can also prove to be effective as it is believed it will release oxytocin that favours birthing.

  • Going herbal has been gaining momentum and many get to share their success stories through this method. Inducing labour with red raspberry leaf tea is a popular practice. The tea is said to tonify the uterus. Evening primrose oil is another herbal remedy. It is unlikely to initiate labour contractions, but it may soften the cervix.


Conclusion

As the due date approaches, the location of your baby in the womb becomes increasingly critical. A few weeks before delivery, most newborns achieve the optimum foetal posture. The obstetrician may try to shift the baby into the head down cephalic position if they haven't moved into it by week 36. One may need a caesarean delivery if you're in an unusual foetal position, such as breech, face-to-mama's-belly, sideways, or diagonal. Other foetal positions can make it more difficult for the baby to glide out and raise the risk of difficulties during labour and delivery. While one has no control over the baby's position while in the womb it is very crucial to have a healthy pregnancy for a birth canal delivery and even the slight error and recklessness can lead to a huge loss that can be draining physically, emotionally and mentally on the mother.

FAQs (Frequently Asked Questions)

1. How is the Fetus Positioned Prior to Birth?

Answer. Birthing Positions for Fetuses indicates when the mother is ready to deliver. The baby should be placed head-down, facing your back, with its chin tucked to its chest and the back of its head ready to join the pelvis during labour. Cephalic appearance is the term for this movement of the baby adjusting to the position. Between the 32nd and 36th weeks of pregnancy, most babies settle into this place.

2. What are the Signs of a Baby Reaching the Birth Canal?

Answer. The belly becomes lower i.e, the belly droops, pelvic pressure increases due to which the pelvic pain also increases, mucus discharge increases, the need to urinate becomes more frequent, back pain is elevated and the mother is hungrier. If the pain is unbearable then immediate care is required and a doctor’s visit as soon as possible will be beneficial. 

3. What are the Ways to Go Into Labour Sooner?

Answer. Sitting or bouncing on a birthing ball has been a popularly recommended way. While some women may go into labour while sitting, spinning, or bouncing on a birthing ball, there is no proof that these balls may help you get pregnant or break your water. The most popular recommendations are walking, doing light squats and even pelvis tilts. All of this must be done with caution and in a gentle manner and only if recommended by a doctor. 

4. What are the Possible Dangers When a Baby Reaches the Birth Canal Passage?

Answer. After the baby is born, it is common to feel some pelvic pain. However, certain forms of pelvic pain can need further investigation. If your pelvic pain is persistent or frequent, see your doctor. Alternatively, if it is followed by bleeding, loss of fluids or dehydration, and fever immediately must be corrected. 

5. What is the Most Common Fetal Position of the Baby Rotation in the Birth Canal?

Answer. The most common position in labour is the left occiput anterior (LOA). The baby's head is slightly off centre in the pelvis in this position, with the back of the head pointing toward the mother's left thigh. During labour, the right occiput anterior (ROA) presentation is also prevalent.