Miscarriage or Miscalculation? Understanding Early Pregnancy Dating Errors
Nothing could be worse than going for an early ultrasound only to find that your baby is ‘’measuring small’ or there is no heartbeat yet. It is indeed one of the most terrifying things to experience as an expecting parent.
For most parents, it triggers so much anxiety when you are waiting to get certainty on the diagnostic report. Sometimes, such conclusions do indicate a potential miscarriage, but it is quite common for the discrepancy to be just a dating error.
If you look at the standard pregnancy dating, it relies on the last menstrual period (LMP). It assumes a 28-day cycle with ovulation happening on the 14th day.
However, just because the menstrual cycles vary between 21 and 35 days, the calculation can be just early pregnancy dating errors, and hence, quite unreliable.
You need to understand the dating process behind the early pregnancies, how irregular ovulation impacts it, and when you should go for a second opinion. All this will help parents manage their anxiety during this uncertainty.
How Early Pregnancy Gestational Age is Calculated
Parents must understand in what scenarios or why a potential miscarriage might actually be a miscalculation. For that, you need to first familiarize yourself with the very concept of calculating pregnancy due date and gestational age.
Using your last menstrual period for dates
The most common method for calculating pregnancy due date is to count 280 days from the first day of your last menstrual period. This is known as the standard 28-day cycle assumption, where it is presumed that every woman ovulates exactly on day 14th of her cycle.
The only problem is that it is often quite unreliable because menstrual cycles vary amongst women, ranging from 21 days to 35 days.
Another reason would be if the ovulation is irregular, as the woman is ovulating earlier or later than day 14th. Also, you have to account for the unreliability of a definitive diagnosis of pregnancy failure from the clinic side due to these variations.
The role of early ultrasounds in pregnancy
Surely, LMP can be a good starting point, but the first-trimester ultrasounds in the medical field are considered to be the gold standard for establishing a more accurate due date.
These scans need to be done at approximately 8 weeks of pregnancy, as this is the time when you can get the most effective result.
During this practice, the measurement used is Crown-Rump Length (CRL). This is the distance from the top of the embryo’s head to its bottom. It is quite accurate because it is measuring the embryo using ultrasound, which becomes more accurate within plus or minus 5 days.
Also, it will override the LMP data if there has been some discrepancy. Parents to lock in the most accurate date, must monitor fetal development, schedule required tests and screenings that are required during that phase.
3 Common Reasons for Pregnancy Dating Miscalculations
The math-based dating and ultrasound results often have discrepancies because both of these methods use different sets of data.
The 28-day cycle method is based on a general assumption, whereas the ultrasound accurately measures the actual physical development of the pregnancy at its most effective period.
Here are the most prominent reasons for miscarriage vs wrong dates.
Irregular ovulation cycles and late conception
So, the mathematical method to find out the due date assumes that women have a 28-day menstrual cycle with ovulation happening exactly on the 14th day.
However, it is not true for many women. Most of the time, the cycle varies between 21 and 35 days. This variation makes the method unreliable.
The best is to go for the 6-week ultrasound as per the LMP, which would actually show a 5-week-old pregnancy, which is a normal variation rather than a sign of failure.
Inaccurate last menstrual period recall
To figure out the due date, you would need to know the exact first day of your last menstrual period. Most of the time, you tend to forget the exact day or remember it uncertainly or just wrong. This changes the due date result, making it not accurate at all.
Fetal development happens faster in the first trimester. So when you are off by a few days due to a wrong LMP recall date, the doctor often fails to locate a heartbeat or measure the fetal pole due to it being so early in the scan.
Natural differences in early fetal growth
The early phase, where the fetus grows, has a predictability to it. However, there are still some variations, both naturally or technically, that can influence the dating.
One of them is inter-observer variation, which is the 15% plus or minus difference that has been seen in different doctors or technicians when measuring the CRL.
Another aspect to add to the technical differences is the scanning problems. So when scanning angles change, it becomes difficult to get a clear picture of the embryo. The ultrasound equipment’s capability and accuracy matter as well.
Measuring Behind: When to Worry and When to Wait?
Parents, mothers particularly have to go through this terrifying and painful period of uncertainty when their early ultrasound reveals that their pregnancy is measuring behind.
However, there are medical guidelines that you should trust to differentiate between the younger pregnancy phase and the non-viable one.
Just suspicion vs. actual diagnosis of pregnancy failure
To avoid rushing to the pregnancy results, mistaking it for a miscarriage, doctors have strict criteria to differentiate their findings that are based on the basis of suspicion or assumption from the actual diagnostic results.
When a CRL of 7mm or greater has no heartbeat, it is officially diagnosed as a failed pregnancy. If the embryo is less than 7 mm with no heartbeat, doctors consider it to be suspicious but not definitive, as oftentimes, the heartbeat might be detectable later. This helps doctors to differentiate between miscarriage or wrong calculations.
Understanding the empty gestational sac
When doctors see a mean sac diameter (MSD) of 25 mm or more with no embryo, they diagnose it as pregnancy failure.
However, if the sac measures somewhere between 16 and 24 mm without an embryo, it is just a matter of suspicion, since oftentimes some pregnancies do not show an embryo until the sac becomes larger.
Also, it is normal to find the gestational sac with no pole or embryo if you are only 5 weeks along. However, if you are at your 7 weeks based on your last period, but then you see an empty sac in ultrasounds, chances are you may have ovulated later than the assumed day 14. So, in this case, you’re just younger than the LMP-based math calculated.
Waiting for the follow up ultrasound scan
When doctors find things to be suspicious, not diagnostic, they will recommend a follow-up scan, usually a week or two weeks later. This wait is essential to give your pregnancy enough time to develop and gain certainty on things.
Coping With Scan Anxiety and Seeking Support
This waiting period is quite stressful and often takes a mental toll, but it is only causing more distress. Also, it is natural to have more anxiety over time during these uncertain phases.
Managing stress during the two-week wait
When you have to navigate through this two-week wait for a follow-up scan, it becomes such a stressful pregnancy phase. But you have to understand that it is medically necessary to give your body time to show some measurable growth, bringing certainty before misdiagnosing anything.
It is necessary for you to manage your stress during this time. For that, you should acknowledge the importance of waiting and seeing as it is the safest medical approach. Rushing to a diagnosis is always a bad idea.
Also, remind yourself that this is just a suspicious phase and not diagnostic. Remember that lack of symptoms like nausea and vomiting, which is often a sign of a healthy pregnancy, doesn’t necessarily mean pregnancy failure.
You can also read so many success stories where an earlier empty sac was detected only to find a healthy baby with a heartbeat right after one or two weeks.
Seeking professional doctor consultations
Still, if you are indeed going through such an uncertain diagnosis, it is better to get more clarity through a second opinion. Changing the practitioner or the clinic and consulting with a more experienced specialist with much more advanced equipment can really help if something was missed earlier.
Key Takeaways
Parents must understand the methods used for dating the pregnancy so they can understand the difference between suspicion or assumption and the actual diagnostics. The discrepancy between the LMP and ultrasound may be due to a simple miscalculation due to inaccurately assuming late ovulation.
Just because the menstrual cycle varies, the math-based dating, which is based on the accuracy of your remembering the date, is much less accurate than the proper diagnostic testing in the first-trimester.
It is important to manage your stress during this waiting period of uncertainty. For that, understand the medical reasoning behind it and account for what it is, which is just a suspicion, not a definitive clinical assessment of pregnancy failure.
You should also explore the alternate methods while you stay positive and wait for your follow-up scan with the R for Rabbit Pregnancy Due Date Calculator. Stay put and let this period pass.
This content is originally published on R For Rabbit' s Website: Miscarriage or Miscalculation? Understanding Early Pregnancy Dating Errors