A perinatologist is a doctor who specializes in high-risk pregnancies. They are also trained as obstetricians, but they don't usually do the deliveries.
If you have had surgery on your cervix, you are considered high-risk. That sounds scary at first since when you're pregnant, all you want is a normal pregnancy and a normal, healthy baby. But it's not bad to get the extra attention to make sure that things go smoothly.
If your regular obstetrician doesn't recommend that you go to a perinatologist, find one yourself. The obstetricians do not monitor your cervix unless you've had a 2nd or 3rd trimester miscarriage in the past. I wouldn't want to wait for that to happen to me.
Perinatologists will be monitoring your cervix length if you've had cervical surgery. They do it by ultrasound. You lie on the table like you would for a Pap smear, and they put an ultrasound probe in your vagina. Usually, they handed the probe to me, and I put it in myself. The probe is like a lubricated banana. They will also do ultrasound through your belly.
You won't go for monitoring until you're at least 12 weeks pregnant. Any miscarriage before that is almost always due to something wrong with the baby, not your cervix. Plus, the baby is so small that it doesn't weigh enough to cause problems to your cervix yet.
It's when you get bigger and the baby gets heavier that your cervix could prematurely dilate. The doctor will be watching for signs of that. On ultrasound, they'll see your cervix start to funnel open if it's happening.
If that happens to you, your perinatologist will probably recommend a cerclage. And maybe you'll also need bedrest.
You will go monthly to the doctor until you're 34 weeks pregnant. At that point, if you were to deliver the baby, everything would be okay. I was walking out to the front desk, ready to make my next appointment, and I asked the doctor when I should come back, and he said, "You're done here!"
Perinatologists are also the specialists who typically do prenatal testing like amniocentesis or CVS. Some obstetricians will do that, too.
Even though I had 3 surgeries on my cervix, I had no problems during pregnancy. What I learned is that the length of your cervix is a genetic gift, and some of us are born with longer cervixes than others. So even though I had quite a bit of my external cervix cut away, I still had a very long internal cervix. It did the job just fine!