When you feel your baby, are they lying sideways (at a 90-degree angle to your spine)? Or are they running in the same direction as your spine? If it’s the latter, you may have a longitudinal lie. Almost all babies are in this position, so there’s nothing to worry about if that’s what you have.
If the baby’s spine is parallel to yours, he or she is in a longitudinal lie. This is the most common type of lie and occurs in about 95% of pregnancies.
There are two basic ways that your unborn baby can position itself: longitudinal or transverse. In a longitudinal lie, the baby is in line with the spine. When a baby is in a transverse lie, it will be at a 90 degree angle to the spine
In a longitudinal lie, the baby’s spine is parallel to your spine. The baby can be lying head down (cephalic), butt down (breech) or side to side (transverse). Most babies are in a longitudinal lie.
When your baby lies parallel to your spine, they are said to be in a longitudinal lie. This is the most common position for birth.
When a baby is said to be in the longitudinal lie position, it means that the spine of the baby runs in parallel to the spine of the mother. These babies are said to be “free-floating.”
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.
Background: Abnormal presentation (detected in the early third trimester) causes concern for pregnant women and their carers. Definitive ultrasound-based data on the risk of persistence of abnormal presentation is lacking to allow appropriate counselling. Comparison of pregnancy outcome was made on the basis of maternal age at delivery.
Methods: Notes of 1010 women (426 primigravidae, 584 multigravidae), with singleton pregnancies, confined between 1997 and 2005 were reviewed to extract: (i) the gestation based on 18-20-week ultrasound in conjunction with the patient’s recorded last menstrual period, and (ii) the presentation of each antenatal visit from 28+ weeks until delivery. Previous obstetric history, maternal age, mode of delivery, birthweight and outcomes were also documented.
Results: At 28-30 weeks, 216 babies presented abnormally. By 38+ weeks, 54 persisted as either a breech or a transverse lie. Thus, an abnormal presentation in the early trimester carries a 22.2% chance of persisting at term. Continuance of abnormal presentation at each subsequent week of the third trimester increased the risk of a Caesarean delivery at term. Conversely, in only six cases, a cephalic presentation at 28-30 weeks converted to a breech or other presentation during the third trimester– a risk of 0.75%.
Conclusion: These statistics provide a useful tool in advising women of the chances of abnormal presentation at term based on the presentation at various stages of the third trimester, and prepare them for the potential requirement of a Caesarean section.
Longitudinal Position of a Baby
Certain terms are used to describe your baby’s position and movement through the birth canal.
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.
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.
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 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.
- 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).
- 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.
- 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.
- 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.
- 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.
- As the baby’s head is delivered, it will rotate a quarter turn to be in line with the body.
- 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.