Are you going to be able to have a vaginal delivery? Will your labor pains be more in your pelvis or your back? The answers to these questions depend in large part of the position of your baby in your uterus as you go into labor. Medical professionals call this position the fetal presentation.
Almost all (95-97%) babies are delivered in head-first or cephalic presentation. Most babies move into the head down position by the third trimester. Cephalic presentation is further broken down by the position of the head; in the vast majority of cephalic deliveries, the crown or top of the head (called the vertex), enters the birth canal first and is the first part of the baby to be delivered. This is why we say a baby is ‘crowning’.
In most cases of vertex presentation, the back of the baby’s head (called the occiput) is toward the front (anterior) of the mother’s pelvis. This presentation is called occiput anterior, and is considered the best position for a vaginal delivery. Around 5% of babies are delivered in the occiput posterior position, where the back of the baby’s head is toward the mother’s backbone and tailbone. This is popularly believed to be the cause of painful ‘back labor’, although the scientific support for this is somewhat lacking. What is known is that the occiput posterior (OP) presentation can significantly prolong labor, and is three times more likely than occiput anterior (OA) presentation to result in cesarean section. This is because the position of the baby makes it harder to pass through the birth canal. Occiput presentation is more common in older and first-time mothers, as well as with larger or overdue babies. Surfing the internet will provide you with many different exercises which claim to prevent occiput posterior presentation, but none of these have been scientifically proven to be of benefit.
Rarely (around 1 in every 800 births), the baby will present face-first instead of with the top of the head. Around 70% of these babies can be delivered vaginally, although the labor may be mildly prolonged. The remainder tend to be delivered by cesarean section either because the labor is not progressing or because the doctor or midwife is concerned about the baby’s heart rate.
Breech presentation occurs when a baby enters the birth canal with the buttocks or feet first, rather than the head. This prevents the cervix (opening to the uterus) from dilating effectively, and can lead to problems with the umbilical cord becoming pinched/compressed. Breech presentations occur in approximately 3-4% of deliveries, and are more likely in premature births and with multiple babies (e.g. twins and triplets). While breech babies can be delivered vaginally, studies have found that vaginal deliveries are around three times more likely to result in serious harm to the baby than cesarean sections. Therefore, in most cases in the US, breech babies are delivered by c-section. Your midwife or doctor may diagnose a breech presentation by physical exam and/or ultrasound.
Shoulder presentation is uncommon, occurring in less than 1% of deliveries. This occurs when the baby is lying sideways in the uterus, rather than head down or buttocks/feet down. If labor starts with the baby in this position, the shoulder becomes wedged in the pelvis and the labor cannot progress. Almost all babies with shoulder presentation will need to be delivered by cesarean section. Shoulder presentation, like breech presentation, is more common in premature babies or in the setting of multiple gestations.
The chances are good that your baby will know which way is up; in the case of labor and delivery, this means head down. Attending your regular prenatal visits will allow your doctor or midwife to keep a close eye on your baby, and plan the safest delivery for the two of you.