#54 The Role of Oxytocin in Labor

When you are in labor, your body produces the hormone oxytocin when your cervix is about 5 cm dilated. This is the point at which you enter what is called the acceleration phase of labor. Oxytocin does several things. Oxytocin causes more prostaglandin to be sent to the uterus to further strengthen your contractions. After your delivery, oxytocin is also important for milk let-down in breastfeeding and promotes bonding with your baby by increasing your sense of smell for the baby.

Oxytocin is made in the hypothalamus, the mother of all glands, located deep inside the middle of your brain. Oxytocin is sent to the posterior (back of) pituitary gland where it is stored and then discharged when there is a need for it, such as in labor or in breastfeeding.

Most hormones have a negative feedback loop. With estradiol, for example, when the level of estrogen increases, the hypothalamus senses the increase and sends a message to the pituitary to decrease or maintain an even or constant level of estradiol.

In a positive feedback loop, exactly the opposite occurs. The hypothalamus sees the level of oxytocin rising and sends a message to the pituitary to increase the oxytocin rather than sending a message to stop the increase. The production of oxytocin is part of what I call the hormone cascade in labor. This cascade is what makes vaginal birth possible.

Pressure on the cervix from your baby’s head also causes the pituitary gland to release more oxytocin. Again, this is part of the crescendo or positive feedback during your natural labor. However, the bioidentical form of oxytocin, Pitocin, can be used to augment labor or induce labor. If your contractions aren’t strong enough, you may be given Pitocin to strengthen your contractions (called augmentation). When Pitocin is given to start contractions when there is no labor, it is called induction.

There are a number of medications to augment or induce labor, but Pitocin is the most commonly used for two reasons. First, Pitocin is affordable, readily available, and easy to use. Most mothers in labor already have an IV in place. This makes giving Pitocin easy and quick to do. Secondly, if your baby begins to show signs of fetal distress, the effect of Pitocin can be quickly removed because it does not last long in your system. Once the Pitocin is stopped, your contractions will return to your baseline quickly, even in just a few minutes.

There have been no real studies of the safety of Pitocin for your baby. The safety and side effects of Pitocin are relatively unknown. Because the Pitocin is usually administered accompanied by an epidural, it is hard to control for the effects of the epidural along with the Pitocin. Along with the use of Pitocin and an epidural, your amniotic sac may be broken before your cervix has dilated to 5 cm. to help labor to progress more quickly. The effect of the combination of these factors in addition to the Pitocin make isolating any effects of the Pitocin itself difficult.

I know of no studies which control for all of these variables simultaneously over time, either for the mother or the baby. I have long felt that using the baby’s head for a battering ram in inductions can’t be good for the baby. But I know of no studies of the results of augmented labors or inductions on the baby. My suspicion is that if we looked, we would find that breaking the amniotic sac early in labor (before 5 cm dilation) would have high risk for negative cognitive outcomes. No one has looked for risks to the baby with labor augmentation or induction.