Ripening the Cervix, and Induction of Labor
a discussion for patients by Martina Nicholson, MD, FACOG
WITH MANY THANKS to Dr. Aaron Caughey, MD, MPP, MPH, PhD, at UCSF, for the expert review of the data and nuances of this topic.
When we wonder about the "best" time for delivery of a pregnant woman, there is now sufficient data about how long the cookies should stay in the oven, so they will come out golden brown, not underdone or overdone. And the answer is 39-40 weeks. There is the lowest chance of morbidity at that time. So now we are trying to get as many babies as possible to deliver within that window of opportunity.
After the edge of "term" there is more risk of the baby being surrounded by inadequate water, so the cord can become squeezed in labor, as the contractions intensify. The cord brings oxygen to the baby, and if it is too "vulnerable" it will not deliver enough, so that the baby gets stressed, and then distressed". This makes it important to try to get through labor when there is still enough fluid around the baby so that the cord can float freely, and pass oxygen in and carbon dioxide out. The placenta is "breathing" for the baby, until delivery.
Also, the baby can go poop in the water, which is called meconium. If the baby takes deep gasping movements, the fluid in the baby's lungs can be so noxious, covering the insides of the lung surface, that the baby can not breathe air when it comes out. The baby has to make a transition from being in a watery world, to being in air, and learning to breathe, rather than get all its oxygen from the placenta, through the umbilical cord. So it is very important for the baby not to gasp and inhale deeply the meconium. We now know that babies gasp as a reflex, when they are inside and there is not enough oxygen. So we want them not to have long or deep fetal heart beat decelerations, which cause them to feel less oxygen, and gasp. Babies can tolerate some stress, some low-oxygen, for awhile. But labor can be long and hard, and if it is getting harder and harder to get enough oxygen, the baby will become "distressed"-- and need to be bailed out.
So a big part of the work of doctors, in watching labor, is to gauge how much stress the baby is under, and whether the baby is bearing up under it. In a fast, easy labor the water is abundant, the cord is not compressed with contractions, and mother's pushing allows a natural squeezing which may help the lungs be less full of water, and more ready to take in air when the baby first breathes.
In a long hard labor, there is also the risk of infection, which can rise from bacteria which naturally live in the vagina, up into the uterus. So it is really important for the mother to be delivered as promptly as possible, to reduce the risk of infection passing to the baby. The mother also can get a deep infection in the walls of the uterus, which is called "chorioamnionitis" (infection in the bag of waters) and later, "endometritis"(infection in the lining of the uterus)--and this causes the walls of the womb to be less capable of contracting efficiently, both in labor, and afterward, to keep from bleeding from the raw site where the placenta was attached.
When a baby is post-dates, and has meconium, and has infection, it is like 3 strikes against them. For this reason, we want to get them delivered when they are ripe but not at risk.
Some women look askance at us, for trying to talk them into being induced at term. They need to understand that this is the underlying reason. For most moms and babies, it is safer, and there is more chance of a successful vaginal delivery, if we don't wait till two weeks overdue.
In general, I try to "let the river flow, rather than trying to push the river". But sometimes we need to nudge someone into labor to get them to deliver in the best window of opportunity for safety.
What stops us? The last process of pregnancy before labor is cervical ripening. If the cervix is like a green apple, it is much harder to get it to open. It needs to be like a ripe peach. The soft, squishy, mushy tissue will more easily begin to open up. So what we now use, to get the "ripeness" we need, is prostaglandins. The medicine Cytotec, or misoprostol, was invented for ulcers, but it was found to be exactly what is needed to make the cervix ripen. This is what does it naturally, in most women. But some women don't make enough. So we can give them this medicine, vaginally or orally, and the cervix will respond by ripening.
After the cervix is ripened, which may take around 24 hours, the uterus can begin to open up the cervix, by contracting. The contractions are like a castle opening a heavy drawbridge. The drawbridge is drawn up and into the castle walls. We sometimes have to use pitocin, a medicine which is dripped into mom through the iv, to help this process of lifting open the cervix.
Another thing that has to happen is the baby has to come down deeper into the pelvis, and make it through the outlet of the bones. Some babies are just too big for the bones of their moms. Others are lying in a position which makes it harder to get through the pelvis. And some have a tight loop of umbilical cord holding them up. Sometimes we can change the mom's position to help get the baby to turn and come through the pelvis. Sometimes we can actually reach in and turn the baby's head a little, to get it to do this.
When the baby is distressed, or there is thick meconium, or the baby has a body which is too big for the mom's bones, we do a Cesarean Section. This surgery has helped millions of babies to be safely born, with lungs which can breathe, and not having severe infections, and so they can stay with their moms and breastfeed, and not need to go to the nursery in exhaustion and need tubes, iv's and oxygen to help them get out of trouble. A lot of people think doctors are making unnecessary interventions, because they do not understand these facts. All our monitoring is to make sure the baby and the mom are both safe through the process of labor. We want to help babies be born safely, and in optimum health, like golden brown cookies!