Pelvis birth canal

4 Types and How They Affect Birth

Your pelvis is a group of bones located in the lower part of your torso, between your lower back and your thighs. It has several important functions, including:

• supporting the weight of your upper body
• acting as a connection point for your lower limbs, as well as various muscles
• helping you stand, walk, or run
• protecting the organs located in or around the pelvic area

The shape of the pelvis often differs between males and females. A female’s pelvis is generally wider and more open than a male’s pelvis. This helps with vaginal childbirth.

Even among females, though, pelvis shape varies. Generally speaking, there are four main pelvis types. The type you have may affect the ease in which you can give birth vaginally

Keep reading to learn more.

Generally speaking, genetics and environmental factors determine the overall shape of your pelvis. In the 1930s, two researchers divided the pelvis into four different types.

They largely based these pelvis types on the shape of the pelvic inlet, which is the upper area of the pelvic cavity. During vaginal childbirth, the baby passes through the birth canal, which runs through your pelvic cavity. The pelvic inlet is at beginning of the birth canal.

The four different pelvis shapes are:

• Gynecoid. This is the most common type of pelvis in females and is generally considered to be the typical female pelvis. Its overall shape is round, shallow, and open.
• Android. This type of pelvis bears more resemblance to the male pelvis. It’s narrower than the gynecoid pelvis and is shaped more like a heart or a wedge.
• Anthropoid. An anthropoid pelvis is narrow and deep. Its shape is similar to an upright egg or oval.
• Platypelloid. The platypelloid pelvis is also called a flat pelvis. This is the least common type. It’s wide but shallow, and it resembles an egg or oval lying on its side.

Remember that these pelvis shapes are more like guidelines as opposed to rules. Pelvis shape can vary greatly among females around the world.

Now let’s talk about how the different types of pelvis shapes can affect childbirth:

• Gynecoid. The gynecoid pelvis is thought to be the most favorable pelvis type for a vaginal birth. This is because the wide, open shape give the baby plenty of room during delivery.
• Android. The narrower shape of the android pelvis can make labor difficult because the baby might move more slowly through the birth canal. Some pregnant women with an android pelvis may require a C-section.
• Anthropoid. The elongated shape of the anthropoid pelvis makes it roomier from front to back than the android pelvis. But it’s still narrower than the gynecoid pelvis. Some pregnant women with this pelvis type may be able to have a vaginal birth, but their labor might last longer.
• Platypelloid. The shape of the platypelloid pelvis can make a vaginal birth difficult because the baby may have trouble passing through the pelvic inlet. Many pregnant women with a platypelloid pelvis need to have a C-section.

In the past, doctors used X-rays to determine the shape of a pregnant woman’s pelvis. While this typically isn’t done anymore, your doctor will still examine your pelvis to get an idea of how it’s shaped.

Another thing to keep in mind: Though the overall shape of your pelvis doesn’t change, hormones released during pregnancy cause some of your pelvic joints and ligaments to relax. This helps with labor and delivery.

Your pelvis and the surrounding tissues have evolved for pregnancy and childbirth. Plus, other factors besides pelvis shape can influence whether you’re able to give birth vaginally. These include situations where:

• the position of your baby is abnormal, such as feet first (breech) or sideways (transverse)
• you’re carrying multiples
• your cervix doesn’t dilate enough
• there are dangerous changes in the baby’s heart rate (distress)
• the baby’s umbilical cord is compressed or prolapsed
• there’s a problem with the placenta, such as placenta previa
• you’ve had a C-section in the past

The pictures below can help you better visualize the different pelvis types. The pelvic inlet marks the beginning of the birth canal.

Share on PinterestFour common types of female pelvis shapes. Illustration by Diego Sabogal

Several health conditions can affect your pelvis and the surrounding muscles. Some examples include:

• Pelvic floor dysfunction. This is when the muscles of your pelvic floor have trouble coordinating to help you go to the bathroom. It can lead to incontinence and pain in your pelvis or lower back. Pregnancy is a common cause.
• Pelvic organ prolapse. Prolapse can happen when the muscles of your pelvic floor weaken. As a result, pelvic organs — like your uterus — can drop or even press out of your vagina. Common causes are childbirth, menopause, and aging.
• Sacroiliitis. Sacroiliitis is when the joint that connects your pelvis to the lower part of your spine becomes inflamed and painful. It can happen during pregnancy or due to an injury or arthritis.
• Osteitis pubis. Osteitis pubis happens when the joint in the front part of your pelvis becomes inflamed and painful. It’s often caused by repeated stress to the area through activities like playing sports.
• Pelvic fractures. This is when there’s a break in one of the bones of your pelvis. Pelvic fractures are often caused by injuries or accidents. Some may require surgery to repair.

If you’re pregnant or planning to become pregnant and have concerns about how your pelvis shape might affect childbirth, speak with your doctor. They can examine your pelvis to help get an idea of how it’s structured.

Remember that many other factors besides the shape of your pelvis can affect whether you give birth vaginally. As with the type of pelvis you have, many of these things are out of your control.

But you should make an appointment with your doctor if you experience any of these symptoms:

• pain or pressure in your pelvic area that’s persistent, recurring, or interfering with your daily activities
• problems with urinary or fecal incontinence
• pain that happens during sex, while inserting a tampon, or while using the bathroom
• feeling like something is coming out of your vagina or seeing something bulging out of your vagina

While pelvis shape can vary widely among females, there are four general types: gynecoid, android, anthropoid, and platypelloid. The shape of your pelvis may affect the ease in which you can give birth vaginally.

The gynecoid pelvis is the most common pelvis shape in females and is favorable for a vaginal birth. Other pelvis types, such as the android and platypelloid shapes, may lead to a more difficult vaginal birth or the recommendation of a C-section.

But pelvis shape alone doesn’t determine how you give birth. Other factors, such as the position of the baby or if you’re carrying multiples, could also lead to your doctor recommending a C-section.

Regular checkups and communication with your doctor are an important part of promoting a healthy pregnancy and delivery. Always attend all of your prenatal appointments and never hesitate to talk to your doctor if you have any questions or concerns about your pregnancy or delivery.

Your baby in the birth canal: MedlinePlus Medical Encyclopedia

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During labor and delivery, your baby must pass through your pelvic bones to reach the vaginal opening. The goal is to find the easiest way out. Certain body positions give the baby a smaller shape, which makes it easier for your baby to get through this tight passage.

The best position for the baby to pass through the pelvis is with the head down and the body facing toward the mother's back. This position is called occiput anterior.

Certain terms are used to describe your baby's position and movement through the birth canal.

FETAL STATION

Fetal station refers to where the presenting part is in your pelvis.

• The presenting part. The presenting part is the part of the baby that leads the way through the birth canal. Most often, it is the baby's head, but it can be a shoulder, the buttocks, or the feet.
• Ischial spines. These are bone points on the mother's pelvis. Normally the ischial spines are the narrowest part of the pelvis.
• 0 station. This is when the baby's head is even with the ischial spines. The baby is said to be "engaged" when the largest part of the head has entered the pelvis.
• If the presenting part lies above the ischial spines, the station is reported as a negative number from -1 to -5.

In first-time moms, the baby's head may engage by 36 weeks into the pregnancy. However, engagement may happen later in the pregnancy, or even during labor.

FETAL LIE

This refers to how the baby's spine lines up with the mother's spine. Your baby's spine is between his head and tailbone.

Your baby will most often settle into a position in the pelvis before labor begins.

• If your baby's spine runs in the same direction (parallel) as your spine, the baby is said to be in a longitudinal lie. Nearly all babies are in a longitudinal lie.
• If the baby is sideways (at a 90-degree angle to your spine), the baby is said to be in a transverse lie.

FETAL ATTITUDE

The fetal attitude describes the position of the parts of your baby's body.

The normal fetal attitude is commonly called the fetal position.

• The head is tucked down to the chest.
• The arms and legs are drawn in towards the center of the chest.

Abnormal fetal attitudes include a head that is tilted back, so the brow or the face presents first. Other body parts may be positioned behind the back. When this happens, the presenting part will be larger as it passes through the pelvis. This makes delivery more difficult.

DELIVERY PRESENTATION

Delivery presentation describes the way the baby is positioned to come down the birth canal for delivery.

The best position for your baby inside your uterus at the time of delivery is head down. This is called cephalic presentation.

• This position makes it easier and safer for your baby to pass through the birth canal. Cephalic presentation occurs in about 97% of deliveries.
• There are different types of cephalic presentation, which depend on the position of the baby's limbs and head (fetal attitude).

If your baby is in any position other than head down, your doctor may recommend a cesarean delivery.

Breech presentation is when the baby's bottom is down. Breech presentation occurs about 3% of the time. There are a few types of breech:

• A complete breech is when the buttocks present first and both the hips and knees are flexed.
• A frank breech is when the hips are flexed so the legs are straight and completely drawn up toward the chest.
• Other breech positions occur when either the feet or knees present first.

The shoulder, arm, or trunk may present first if the fetus is in a transverse lie. This type of presentation occurs less than 1% of the time. Transverse lie is more common when you deliver before your due date, or have twins or triplets.

CARDINAL MOVEMENTS OF LABOR

As your baby passes through the birth canal, the baby's head will change positions. These changes are needed for your baby to fit and move through your pelvis. These movements of your baby's head are called cardinal movements of labor.

Engagement

• This is when the widest part of your baby's head has entered the pelvis.
• Engagement tells your health care provider that your pelvis is large enough to allow the baby's head to move down (descend).

Descent

• This is when your baby's head moves down (descends) further through your pelvis.
• Most often, descent occurs during labor, either as the cervix dilates or after you begin pushing.

Flexion

• During descent, the baby's head is flexed down so that the chin touches the chest.
• With the chin tucked, it is easier for the baby's head to pass through the pelvis.

Internal Rotation

• As your baby's head descends further, the head will most often rotate so the back of the head is just below your pubic bone. This helps the head fit the shape of your pelvis.
• Usually, the baby will be face down toward your spine.
• Sometimes, the baby will rotate so it faces up toward the pubic bone.
• As your baby's head rotates, extends, or flexes during labor, the body will stay in position with one shoulder down toward your spine and one shoulder up toward your belly.

Extension

• As your baby reaches the opening of the vagina, usually the back of the head is in contact with your pubic bone.
• At this point, the birth canal curves upward, and the baby's head must extend back. It rotates under and around the pubic bone.

External Rotation

• As the baby's head is delivered, it will rotate a quarter turn to be in line with the body.

Expulsion

• After the head is delivered, the top shoulder is delivered under the pubic bone.
• After the shoulder, the rest of the body is usually delivered without a problem.

Shoulder presentation; Malpresentations; Breech birth; Cephalic presentation; Fetal lie; Fetal attitude; Fetal descent; Fetal station; Cardinal movements; Labor-birth canal; Delivery-birth canal

• Childbirth
• Emergency Childbirth
• Emergency Childbirth
• Delivery presentations
• C-section - series
• Breech - series

Barth WH. Malpresentations and malposition. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 17.

Kilpatrick SJ, Garrison E, Fairbrother E. Normal labor and delivery. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 11.

Updated by: LaQuita Martinez, MD, Department of Obstetrics and Gynecology, Emory Johns Creek Hospital, Alpharetta, GA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A. D.A.M. Editorial team.

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