Lower Segment (Transverse)
- Thin myometrium therefore less blood loss, quicker entry
- Lower risk of catastrophic uterine rupture in future pregnancies
- Width is restricted by uterine arteries and Azygos plexus
- May have to create a “T” incision to obtain adequate exposure
The choice of uterine incision largely depends on the indication for cesarean section. Most cephalic, term babies delivered in labour can be delivered by lower segment incisions. This has the advantage of providing quick access to the uterus through relatively attenuated, avascular tissue. A small nick is usually made in the midline. The incision is extended bluntly or with bandage scissors.
In order to expose the lower uterine segment and mobilize the bladder, the peritoneum of the bladder reflection is elevated and incised in a transverse manner, being careful to stay cephalad to the bladder itself.
Cross section shows blunt dissection of the bladder off the uterus to expose the lower uterine segment.
The bladder is surrounded by a reflection of peritoneum that covers the lower uterine segment. In order to expose the lower segment and avoid injury to the bladder, the operator must ensure that the bladder is displaced caudally before making the uterine incision. In primary cesarean sections, the bladder may retract spontaneously. In repeat cesarean sections, sharp dissection of the bladder flap may be required.
The anterior wall of the lower segment of the uterus is entered gradually, with successive, superficial strokes of the scalpel alternating with sponging to allow good visualization. The cavity is entered carefully in the midline either with a scalpel or grasping forceps. Ideally, the amniotic sac should be left intact unless spontaneous rupture of the membranes has already occurred. Make a slightly curvelinear transverse uterine incision, avoiding lateral blood vessels.
The uterine incision is extended laterally with the fingers or with bandage scissors. The incision should form a “smile” with the corners elevated away from the large vessels of the lateral to the lower segment. Once the uterine incision is completed the amniotic sac is ruptured with forceps and fluid is allowed to drain out so the baby will settle in the pelvis.
- Excellent exposure
- Useful when lower segment is not developed (useful breech or transverse lie, prematurity)
- Once a (classical) cesarean, always a cesarean
- Thick myometrium means slower entry with more blood loss
- More difficult closure (three layers)
A less commonly performed uterine incision is the so called classical (or vertical) incision. It is reserved for those rare instances when a lower segment incision is impossible or contraindicated. These circumstances may involve fetal factors where the presenting part has not adequately advanced to distend the lower uterine segment. This may occur with prematurity, footling breech presentation, transverse lie or a combination of these factors. Closure of the incision is more difficult and involves more blood loss due to the thickness of the myometrium in the upper uterine segment. Once a classical cesarean section has been performed, future trial of labour is contraindicated.
An initial small vertical hysterotomy incision is made in the lower uterine segment. Fingers are insinuated between the myometrium and fetus to avoid fetal laceration. Scissors extend the incision cephalad as needed for delivery. (Reproduced with permission from Johnson DD: Cesarean delivery. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al (eds): Cunningham and Gilstrap’s Operative Obstetrics, 3rd ed. New York, McGraw-Hill Education, 2017.)
The vertical incision is made in the midline of the body of the uterus cephalad to the bladder reflection. Again successful, superficial cuts with the scalpel are made until the cavity is entered. The incision is then extended with bandage scissors.
Uterine Incision – other considerations
Extension: t incision-extend in midline-? More bloodloss. J incision –extend one corner cephalad into contractile portion of myometrium or U incision (both corners)
Anterior placenta: if low lying anticipate poorly formed, vascular lower uterine segment. if unable to detach or avoid it may have to deliver through rapid transplacental access-be aware bleeding can be severe.