With the advent of reliable early pregnancy tests, and the increase in use of fertility technology, ultrasounds early in pregnancy have moved into standard practice in many areas of the United States. In some cases this is a very good thing, providing early knowledge of problematic complications like molar or ectopic pregnancies. Women who have struggled with infertility, or experienced miscarriages, may feel profoundly relieved to see the tiny little sac and fetal pole, and be told that all is well. Although confirmation of viable pregnancy by ultrasound has eased the fears of many women, this practice has another, less adorable side.
Although the fetal heart begins to beat in week 6 of the pregnancy (week 4, if you count from conception), the baby in the womb is only about 1/6-1/4 inch long.1 Take a look at a ruler–that is incredibly tiny. An ultrasound done at 6-7 weeks may not detect a heartbeat. In some cases, this may be because the pregnancy is not viable, the baby has not developed properly, or a miscarriage or ectopic pregnancy may be the cause. However, an ultrasound at this early stage may also simply miss an existing heartbeat, and the entire fetal sack may be hidden due to a variety of reasons. The position of the uterus may be abnormal, hiding the tiny fetus, and excess fat in the abdominal area may compromise the accuracy of the ultrasound.2 Miscalculation of the date of the pregnancy is also a strong possibility, especially in women who have irregular cycles, unusual cycle lengths, or who have been recently pregnant, or are breastfeeding.
If this possibility were well known, and if practitioners were willing to wait rather than easily diagnosing miscarriage or non-viability, and if women were capable of not worrying when told “Hmmm, I don’t seem to see a baby here”, this wouldn’t necessarily be a problem. Unfortunately, these things are not true across the board. First and foremost, however faulty the expectation may be, women expect to see a baby at a 6 week ultrasound. At the very least they expect to see a little “bean” that professionals tell them is their burgeoning little one, and hear a heartbeat. So when no fetus is visible, and not heartbeat audible, there is an immediate and profound sense of worry.
The Journal of Family Practice provides an interesting (though somewhat old) study of two cases where “blighted ovum” and non-viability were raised as probabilities, and later proven very wrong. The conclusion?
“The cases presented here suggest that actions to terminate a potentially nonviable pregnancy based on the available laboratory and radiographic data would have led to the unwarranted destruction of two healthy fetuses.” 3
On a more personal and non-professional level, there is a website dedicated to the support of women who have had a “misdiagnosed miscarriage”4 or are wondering if an ultrasound and blood work at 5-7 weeks gestation is truly the final word on the viability of their baby. The forums supported by the website contain many anecdotes of miscarriage predicted or diagnosed, and then further testing revealing perfectly viable babies–the reasons for these misdiagnoses include all the possibilities discussed above, from mis-dating to inexplicable “hidden” babies. These stories are current, so while the study may be older, it’s clear that 2 decades of advancement in reproductive technology has not eliminated the possibility of erroneous diagnosis of miscarriage. A few of these women, as well as an acquaintance of mine, report being pressured by their doctors to immediately induce miscarriage or schedule a D&C. As you might imagine, those who subsequently found that they were carrying healthy, viable babies were more than a little upset by such behavior.
Of what value is all this to pregnant women? Whether or not we should move away from early ultrasounds is a matter for the medical professionals. Most would probably consider the margin of error acceptable because some early ultrasounds allow for immediate intervention when complications arrives, and possibly save lives in the case of ectopic pregnancies. But newly pregnant women may want to bring up the subject with their care provider, and consider holding off for a few weeks if there is no medical indication for an ultrasound at 5 or 6 weeks gestation. A week or two, or even a few days, can make a world of difference in what can be seen on the ultrasound screen. If an ultrasound is indicated, knowing that error is not only possible but rather common can give a woman at least a shred of hope, and may allow her to wait for further testing with more confidence. It may also give her the ability to resist pressure to immediately medically induce a miscarriage, if it is not medically necessary and a distasteful prospect for her.
1Fetal Development: The First Trimester, staff, Mayo Clinic
2Ultrasound:Sonogram, staff, American Pregnancy Association
3Determining the viability of early pregnancies: Two case studies, October 1991, Pamela M. Davis, Journal of Family Practice