As the baby prepares for delivery, fetal positioning shifts. This change in orientation, known as fetal presentation, is necessary for a smooth vaginal birth. The optimal position is the head-down orientation, medically termed cephalic presentation, where the head is positioned over the mother’s cervix. This orientation is a primary factor influencing the safety and ease of labor and delivery.
The Typical Timeline for Head-Down Position
Most babies naturally transition to the head-down position during the third trimester of pregnancy. This typically occurs between 32 and 36 weeks of gestation, or roughly the eighth month. The 34- to 36-week mark is when healthcare providers commonly monitor the baby’s position closely.
This natural turn is driven by the physical mechanics of the developing fetus and the uterine environment. As the fetus grows, the head becomes the heaviest part, and gravity encourages it to drop toward the lower, narrower segment of the uterus. The shape of the pear-shaped uterus naturally accommodates the bulkier head in the lower pole. By 36 weeks, the vast majority of babies, about 97%, have settled into this vertex presentation.
Understanding Fetal Position Terminology
Fetal presentation describes the part of the baby closest to the birth canal and is classified into three main categories. The most desired orientation is the cephalic presentation, meaning the baby is positioned head-down. Within this category, the safest is the occiput anterior position, where the baby faces the mother’s back.
A less common, but still head-down, position is the occiput posterior, where the baby faces the mother’s abdomen. The other two main presentations are breech, where the baby’s buttocks or feet deliver first, and transverse lie, where the baby lies horizontally across the uterus. The transverse lie is the rarest, occurring in less than 1% of pregnancies at term.
When the Baby Remains Breech
If a baby has not turned head-down by 36 or 37 weeks, they are considered a breech presentation. Breech is categorized by the position of the baby’s legs, with three main types. Frank breech is the most common, where the baby’s hips are flexed and the legs are extended straight up toward the head.
The complete breech involves the baby sitting cross-legged with the hips and knees both flexed, while a footling breech occurs when one or both feet are positioned to deliver first. Delivery of a breech baby carries increased risks because the head, the largest and least compressible part, delivers last. This delay can lead to the umbilical cord becoming compressed, potentially cutting off the baby’s oxygen supply, a condition known as cord prolapse.
To encourage the baby to turn, a medical procedure called External Cephalic Version (ECV) may be offered around 37 weeks gestation. During an ECV, a healthcare provider applies firm pressure to the mother’s abdomen to manually rotate the baby from the outside. This procedure, performed where an emergency cesarean section is possible, has an overall success rate averaging around 58% to 65%. If the baby remains breech after 37 weeks and ECV is unsuccessful, a planned cesarean section is typically scheduled.