When exactly is a trans-vaginal ultrasound actually medically necessary or advisable?
I work in high risk pregnancy and most of the ultrasounds I assist with are done at later than 20 weeks gestation.
Transvaginal or abdominal ultrasound can be used early in pregnancy when the embryo/fetus is very small (12 weeks or less). This measurement is usually just ‘crown-rump’ length and is used to ‘date’ the pregnancy. Women often have this done on the first or one of the first visits to the OB-GYN. Many OB-GYNs have a small ultrasound unit in their clinic for this ‘dating’ US or refer to a local radiology department for the procedure. Most women would not like to have a vaginal probe US at this gestation (or any gestation, really) if an abdominal US would do. Most likely, she would get the abdominal US and only get the vaginal if the Doc really needed a closer look- if there was something unusual such as a strange looking embryo or multiple embryos or a questionable cervix.
A vaginal probe is also used sometimes later in the pregnancy if the patient is very heavy and has too much abdominal tissue for the abdominal approach, but this does not allow for very complete fetal measurements due to the limited visibility. These later ultrasounds are done abdominally so that multiple measurements can be made. Head circumference, abdominal circumference, and femur length measurements are used to calculate the approximate weight and gestation. This later ultrasound usually looks at fetal organ development, too- things like brain, heart, stomach, kidneys. A vaginal probe ultrasound here would probably not allow for all these measurements to be made.
A vaginal probe ultrasound is particularly useful for looking at the cervix for women with know or suspected cervical problems. The length and condition of the cervix (Is it opening? Funneling?) is very easily measure with a vaginal probe although the abdominal approach can be useful here, too. The hallmark for incompetent cervix is painless dilation of the cervix with loss of pregnancy in the second trimester. If the woman has had losses, any cervical procedures such as a cone biopsy or LEEP, or some kinds of fertility treatments, a vaginal or abdominal examination of the cervix would be prudent throughout the pregnancy. If we are really worried about the cervix or it is known to be dilated or have a bulging bag of water, etc. we won’t even enter the vagina and just do a trans-labila US. Again, that may give a limited view, but it’s worth a try.
I had one in early in both of my pregnancies. I believe it was at the first prenatal appointment, at 8 weeks. My doctor recommended an early U/S to get the due date as accurate as possible, and early U/S have to be transvaginal. The earlier the more accurate the date.
Due dates as traditionally assigned are based on a 28 day menstral cycle (with conception around day 14). If a given women’s cycle is significantly longer or shorter, the due date will be off. This has real implications on things like induction, timing of other procedures, etc. So it was recommended to me and I agreed.
My wife has had several of them due to miscarriages and miscarriage scares early in pregnancy.
I use them regularly to rule ectopic pregnancy in first trimester patients.
It seems so intrusive and expensive, just to determine a, still less than accurate, due date, to me. Not much better than counting back your periods. I can understand it for special cases. But routinely?
Anything to do with ovaries: I’ve had thirty or more, as they are a vital part of any fertility treatment that involves stimulating ovulation. The vaginal ultrasound allows you to see the follicles developing. You have one every two or three days. I also had an earlier ones to check my ovaries for cysts.
I didn’t mind them at all, but then I don’t really have much modesty around doctors. The probe is significantly larger than a tampon, but smaller in girth than a penis, and a decent tech is very gentle. There was no physical discomfort. That doesn’t mean it would be ok for the state to compel me to have one.
An ultrasound date in the first 8 weeks is accurate to within 96 hours, and most of the time it’s better than that. Counting back to your last period can be off by a couple of weeks for many, many women as ovulation can be irregular. This accuracy really, really matters if later the woman has preeclampsia or something and you are deciding when to induce. And in the context of an OB office and all the things they do to you there, they aren’t that intrusive. Which still doesn’t make the state compelling them acceptable.
Yup, ovaries. My mother had one as part of diagnosing what turned out to be ovarian cancer. I get 'em because my mother has ovarian cancer. 
I had one after my IUD insertion, to make sure it was where it was supposed to be.
The tech had a hard time finding it, so she went and got another tech and had me hold the other end of the probe until she got back. Which was… well, I can’t decide if it was hilarious or hideously humiliating, but it was one of the two.
Not to go off-topic in GQ, but I wanted to emphasize how this fulfills the OP’s phrase “medically necessary”.
Yes, they are commonly used in fertility treatments. In fact, I’m sitting in the waiting room of my clinic right now waiting for one. I’m in the middle of an IVF and today they’re checking my ovaries to see how many follicles I have.
Off the top of my head:
- Ectopic pregnancy
- PID and hydrosalpinx
- Uncommonly used for fetal dating ultrasound, as it is invasive, and the ultrasound would get blamed if there’s a miscarriage. Easier to do an abdominal one, and the data is excellent for calculating dates.
- Ovaries, especially if you want a good view
- Endometrial thickness - usually if it’s too thick on abdominal imaging
- Cervical thickness - in late gestation, if you’re worried about early labor
- Placenta previa or other anatomical concern regarding delivery in late gestation.
I had one near the end of my second pregnancy because the baby was really low and they couldn’t get a specific measurement with the abdominal. I actually had to do the initial insertion, not the doctor. She took over from there, but I had to put it in.
With both of my pregnancies the fetus was dated at around 9 weeks with an abdominal ultrasound.
It also seems odd that the measurements still seem to be quite inaccurate: as far as I know, it’s still quite common to be early or late.
I had one as a teen to help diagnose amenorrhea. It showed all the cysts on my ovaries. I had not been sexually active yet and it was extremely painful. I guess they don’t make the tool in children’s sizes.
You mean for the baby to be early or late? That’s because the pregnancy doesn’t take exactly 288 days–whatever the trigger is for labor, it’s not simply days past conception. I mean, I know when I conceived to within 12 hours, but I still went into labor 4 days after my due date.
But the dating scans are pretty accurate, and the point of accurate dates isn’t so you know when the baby will come, but so you know when to look for things (like when to do an anatomy scan) and so (most importantly) you know when the baby is done enough, if it turns out you need to induce.
Measurement by transvaginal ultrasound early in pregnancy is accurate +/- 3 days.
Edit: Should have reloaded the threat. Basically, what Manda JO said.
When I tested pregnant while using an IUD and bleeding erratically, they did one to see if there was actually anything implanted. Turns out there was, but it was on its way out. They did another one a few days later to make sure all the cells that needed to go were gone on their own. I guess there’s some chance of parts of the pregnancy hanging around, which could make me very ill if not removed.
I have since wondered, if they had had to go in to remove the dead cells, would that be considered abortion by people who want all abortion illegal, since they were once part of a living human embryo? The actual ending of the pregnancy, my body did itself before I had any clue it was happening.
Do you have a good cite for this, because if this is the case then my ex lied to me as they told us something that was a week to 10 days before I know we were together.