Most babies come out headfirst, facing toward the mother’s back, through the vaginal opening. About 95% of babies settle into this head-down position by the end of pregnancy. The journey from uterus to the outside world involves the baby navigating a surprisingly tight, curved path through the pelvis, making a series of rotations along the way.
The Head-Down Position
In the most common birth position, the baby is upside down with the back of their head pointing toward the mother’s belly button. This position works well because the back of the skull is the smallest, smoothest part of the baby’s head, making it the easiest shape to fit through the pelvis. Babies typically settle into this position weeks before labor begins.
Not all head-down babies face the same direction, though. About 10% to 20% of babies in the pushing stage face upward toward the mother’s belly instead of toward her spine. This “sunny-side up” position makes delivery harder because a wider part of the skull has to fit through the pelvis. The further the baby’s head is rotated away from the ideal face-down position, the higher the chance of a longer labor or complications. Many sunny-side-up babies rotate on their own during labor, but some don’t.
How the Baby Moves Through the Pelvis
A baby doesn’t simply slide straight down. The pelvis is an irregular bony ring, wider in some spots and narrower in others, and the baby has to twist and turn to fit through it. These movements happen naturally in response to the pressure of contractions pushing the baby against the pelvic bones.
The sequence looks roughly like this: the baby tucks their chin to their chest, making their head as compact as possible. As they descend, they rotate so the back of their head lines up with the widest part of the pelvis. Once the head clears the pelvis, it tips backward (extending) as it passes under the pubic bone and emerges from the vaginal opening. After the head is out, the baby rotates one more time so the shoulders can slip through the same narrow space. The rest of the body follows quickly after the shoulders.
Doctors and midwives track this descent using a numbering system from negative 5 to positive 5. Zero means the baby’s head has reached the middle of the pelvis, at the level of two bony bumps called the ischial spines. Each number represents roughly one centimeter of progress. At positive 4 or 5, the baby’s head is visible at the vaginal opening.
How Long It Takes
The cervix, which is the opening at the bottom of the uterus, needs to thin out and open to about 10 centimeters before the baby can pass through. During active labor, first-time mothers dilate at an average rate of about 1.2 centimeters per hour, meaning active labor lasts around 6 hours on average. But there’s a wide range of normal. Up to 30% of first-time mothers dilate slower than 1 centimeter per hour, and for some, active labor can stretch to 13 hours or more without anything being wrong.
Pushing comes after full dilation. For first-time mothers, this stage can last anywhere from 20 minutes to a few hours.
When Babies Come Out a Different Way
About 3% to 4% of babies are still in a breech position at the end of pregnancy, meaning their bottom or feet are pointing down instead of their head. There are three types of breech:
- Frank breech (50% to 70% of breeches): the baby’s bottom comes first, with legs folded up toward the face like a pike position.
- Complete breech (5% to 10%): the baby sits cross-legged in a cannonball shape.
- Footling breech (10% to 30%): one or both feet dangle down and would come out first.
Breech is much more common earlier in pregnancy. Between 22 and 25 weeks, as many as 25% of babies are breech, but most flip on their own as they grow. Because breech vaginal delivery carries higher risks, most breech babies in the U.S. are delivered by cesarean section.
Cesarean Delivery
In a cesarean birth, the baby comes out through an incision in the mother’s lower abdomen and uterus. The surgeon cuts through skin, a layer of fat, the tough tissue covering the abdominal muscles, then separates the muscles (rather than cutting through them) to reach the abdominal cavity. The bladder is moved down and out of the way, and then the uterus itself is opened. The uterine wall has three layers that are all cut through. If the amniotic sac hasn’t already broken, the surgeon opens it, and the baby is lifted out.
The entire delivery part of a cesarean usually takes only about 5 to 10 minutes, though closing everything back up takes longer.
What Happens to the Mother’s Body
During vaginal birth, the baby’s head stretches the tissue between the vaginal opening and the rectum (the perineum). Tearing is common, especially for first-time mothers. Tears come in four levels of severity. First-degree tears are shallow, involving only skin. Second-degree tears go into the muscle beneath the skin and are the most common type that needs stitching. Third-degree tears extend into the muscle surrounding the anus, and fourth-degree tears go all the way through to the rectal lining. Most tears heal well, though deeper ones take longer and require more careful repair.
After the Baby: The Placenta
Birth isn’t quite finished when the baby is out. The placenta, the organ that nourished the baby throughout pregnancy, still needs to detach from the uterine wall and be delivered. This typically happens within 6 to 10 minutes, pushed out by a few final uterine contractions. The median time is about 6 minutes. If the placenta hasn’t come out within 30 minutes, the risk of complications like heavy bleeding increases, and the medical team will intervene.