At this point, a cone biopsy is done. But, unlike a colposcopy, a cone biopsy is a big deal in pregnancy, because the doctor must whittle away at the cervix--that very structure holding the baby in the uterus. The depth of a cone biopsy will determine how weakened the cervix will become. Any weakening increases the risk of incompetent cervix and preterm labor and delivery.
There is a dividing line between the internal cervical cells and the external cervical cells. Since this "transformation zone" is the area where the internal cells are converted to external ones, this is where all of the action is. So if there's a pre-cancerous lesion, this is the place it's going to happen.
A cone biopsy usually must encompass this transformation zone to get a sample with "margins free" of cancerous cells. Luckily, in pregnancy the transformation zone is hormonally stimulated to be more external than internal, meaning that a shallower cone is possible to get the lesion. This is a break for the developing baby before term. But the later in the pregnancy the cone biopsy is done, the more risk of unreasonable bleeding and with it premature delivery.
This is why, if there is a problem, it is best that it be found as early in the pregnancy as possible. A pap smear should be part of the initial evaluation on every newly pregnant patient.
What Pregnancies Are Most at Risk?
Generally, a woman who has kept routine GYN appointments before becoming pregnant will not have a need for a cone biopsy, because progression to that point so quickly is unlikely if recent Paps have been normal. The woman who might need a cone biopsy in pregnancy is one who hasn't had a Pap smear in several years. In her case, an abnormal Pap smear may represent a lesion that has had time to extend up the canal.
Cervical dysplasia is not a reason to terminate a pregnancy. Dysplasia is not cancer. And although all cervical cancers begin with dysplasia, not all dysplasias go on to become cancer. Only when there's invasive cervical cancer does the ethical problem of termination come up. But this need not be a consideration for the pro-life patient when the invasion is "microinvasive" (less than 3 mm of invasion into the cervix) as long as it doesn't get worse. There is a theoretical risk of spreading the disease by labor and vaginal delivery, indicating C-section as the mode of delivery. Abnormal Pap smears are common, and colposcopy will put the right perspective on things.
Because cervical cancer is a leading cause of death in women of childbearing age, it is something that can occur in the pregnant patient. With good routine care, however, pregnancy usually will be complicated only by pre-cancerous (dysplastic) lesions that require only a conservative approach that might be anything from just doing periodic colposcopy all the way to cone biopsy. But unless there's invasive cervical cancer, the pregnancy should progress just fine--as should Mom!