I had a growth ultrasound last week, at 32 weeks, and it went well, despite my fears. In this post, I describe what makes me so nervous about growth ultrasounds, and how they are sometimes interpreted by doctors.
As many of you probably know, diabetic babies undergo growth ultrasounds because of the concern that mom's high blood sugars may send too much juice to the baby, who then gets too big to be delivered vaginally. Either the baby doesn't fit through mom's pelvis at all in vaginal delivery (cephalo-pelvic disproportion, although an artificial variant of it) or the shoulders get stuck after vaginal delivery of the head (shoulder dystocia). If the doctor believes, based on growth ultrasounds, that the baby is or may grow too large to deliver vaginally, the doctor may induce early (38 or 39 weeks) or schedule a c-section.
When I was pregnant with my first son, I had a growth ultrasound at 28 weeks. This is right at the beginning of the third trimester, and when the first growth ultrasound is usually done. They are often done at three week intervals after that until the baby is born. Now, with my first son, I was tentatively prepared for a baby that looked "too big," and planned to ask my doctor to let me try a vaginal delivery even if the baby looked large on the ultrasound. I might have even considered induction at 40 weeks.
Much to my surprise, my son turned up in the third percentile. I was prepared for a baby that was too big, but not one that was too small. I was hospitalized overnight for possible intrauterine growth restriction, which the radiologist that read the ultrasound chalked up to a complication of my diabetes. Fortunately, my obstetrician, with good prudence, sought a second opinion for me. The ultrasound the next day at a different clinic showed a baby in the 35th percentile. I was still on bed rest for a couple of weeks, until they could get a good showing after some time had elapsed, but he continued to be within a normal range for the rest of the pregnancy.
As it turns out, the first ultrasound technician's measurements were just off. So thousands of dollars (including the cost to me, who had to pay my deductible and co-insurance, my insurance company, who was stuck with the rest of the bill, the hospital, whose charges are often written off by the insurance company, and my employer, who lost two weeks' worth of work from me but still paid me for my sick leave) and days of frustration and anxiety later, we were back to a healthy, basically low-risk pregnancy. Now do you understand a little more about why I am afraid of growth ultrasounds?
So what have I learned about growth ultrasounds and why am I anxious about the way doctors use and interpret them? Please keep in mind that all of my observations below are based on the premise that inductions and c-sections should be avoided with more rigor than they are avoided at the present time by many doctors, and that a baby "too large" to deliver vaginally can be avoided with good blood sugar management.
Doctors that are nervous about your diabetes may attribute ANY possible problem to your "condition." The radiologist that read the ultrasound for my first son at 28 weeks assumed that the reason my baby showed up in the third percentile was a result of my diabetes, or the fact that I was jogging at the time (which she said can sometimes result in really small babies). The real problem? An ultrasound technician that didn't take the measurements correctly. My diabetes and my exercise habits were blamed for a measurement error, and resulted in a costly hospital stay and a huge shot to my confidence.
Weight measurements on ultrasound are sketchy at best. I know of a woman who was told that her baby would be too big to deliver vaginally (estimated at 9 pounds). She was scheduled for a c-section and, lo and behold, the baby was only a little over 7 pounds. Most ultrasound technicians and radiologists will tell you that measurements can be up to a pound off anyway, on a good day. So how does that help me? If my ultrasound shows an 8 pound baby, I may be looking at delivering a 7-pounder or a 9-pounder anyway, just within the NORMAL range of ultrasound variability.
How often are babies really "too big" to be delivered vaginally? I'm not sure who knows the answer to this question, but I am skeptical that it occurs very frequently. Even skinny women deliver 9 pound babies all the time. A doctor's intuition may be well-developed in this regard, but it may also be developed by a sense of fear and lack of confidence in your ability to deliver your baby.
How often does a diabetic woman have a genetically large baby that would have been large no matter how well her blood sugars were controlled? Again, I'm not sure who knows the answer to this question, but I also suspect may happen sometimes too. Someone's baby is setting the 95th percentile mark, even apart from diabetes, and it could be you (or me, as the case may be right now)!
Now, I hope I haven't caused anyone to get uppity with their doctor about going for growth ultrasounds. But if your growth ultrasound shows "problems," I would ask yourself and the doctor a few questions about it:
Can I get a second opinion? See if you can find another clinic that's willing to do another ultrasound for you. This will help if it's a measurement error or if it your practitioner has offered an overly-cautious interpretation of the one you already have. Especially if it can help you avoid unnecessary hospitalization or a c-section, your insurance company shouldn't be too hard to get on board.
Which fetal measurements are driving up the weight estimate? Typically, if the baby is growing too large because of uncontrolled blood sugars, radiologists expect to see large trunk measurements. If it is the baby's head that is large, or limbs that are long, it may be more related to genetic factors, especially if your A1Cs are well-controlled (less than 6.5).
Are there any other indications that your baby is large? Other indications, albeit much less precise than ultrasound, include fundal measurements (centimeters should be about equal to weeks of pregnancy, or at least growing steadily, not jumping ahead) and your weight gain. Weight gain, however, is extremely variable from woman to woman, so it wouldn't be good to assume your baby is too big just because you've gained 40 pounds and you are only at 35 weeks. On the other hand, if you have only gained 20 pounds at 35 weeks, you were of a normal weight to begin with, and your fundal measurements have grown steadily, you have one more reason to suspect that the growth ultrasound measurement may not be giving you the best indicator of your baby's true size and your ability to deliver it.
Have you had multiple growth ultrasounds, and have all of them indicated a baby that is "large for gestational age"? Since a pre-existing diabetic's blood sugars will probably be controlled for in approximately the same way throughout pregnancy, given her ability to control them and her prenatal care, it seems possible that if the baby's measurements suddenly jump ahead at 37 weeks, the problem could be one of measurement error, rather than glucose control.
How large are you and the baby's father? I think it is reasonable to expect that the progeny of tall, large-boned, or large-headed (and I'm not talking arrogant) men and women will be tall, large-boned, or have large heads. This may drive up weight measurements.
Are there any other risk factors indicative of induction or c-section? I suspect that doctors may use a baby that's "too big" as icing on the cake to convince a mom that induction or c-section is necessary, when the root of their concern lies elsewhere - mom's high blood pressure, other concerns for baby's development, and so on. These root factors may give good reason for an induction or c-section, but should be identified apart from a baby that's "too big" for you to deliver. It will only undermine your confidence to be told "I don't think you can deliver this baby" when the real concern is for yours or your baby's health.
Is there any reason I shouldn't be offered the opportunity to deliver vaginally, even if it is suspected that the baby truly is larger than he/she should be? Ask your doctor for a "trial of labor," how long he or she is willing to let you remain in your labor trial, what evidence during labor would indicate that the baby really is too big to fit, and if the doctor has any other concerns in handling delivery of a large baby. First-time labors can last a while (a couple of days), so be sure to account for this when you make your plans.
Are you afraid of labor and/or being a mom? If you are told that you have a large baby, does that make you even more afraid of labor? I think I speak universally for parents when I say that pregnancy, labor, delivery, postpartum recovery, and other parts of parenthood will hurt, emotionally and physically. I wouldn't let a baby that's "too big" scare you into a bad decision (unless, as I mentioned, there are other real health factors at play). Better to understand your fear and approach the pain in the most direct, healthy way possible than run away or try to avoid it. My belief is that facing pain bravely and patiently can, in fact, help you establish good parenting habits.
The report from my growth ultrasound was a good one. My son's weight is 60th percentile, with long monkey limbs driving up the weight measurement and a skinny little trunk (just like his daddy).