Objective
To compare the estimated date of confinement of paper gestational wheels to the estimated date of confinement of APPs wheels using a standard last menstrual period.
Methods
Obstetric providers were asked for their gestational wheels. The last menstrual period was set at Jan. 1, 2013, and the estimated date of confinement obtained was compared with the estimated date of confinement of Oct. 8th if the pregnancy completed 280 days. The process was performed on 20 electronic APPs downloadable to cell phones. The process was repeated for both for the leap year of 2012.
Results
Thirty-one paper wheels from a variety of sources were collected. Ten wheels (35%) were consistent with the standard pregnancy duration of 280 days. Among the wheels surveyed, the largest discrepancy was 4 days short of 280 days. Two wheels gave an estimated date of confinement that differed from each other by 7 days. Wheels from the same source did not agree with each other. Twenty electronic gestational age calculators were examined. All 20 gave an estimated date of confinement of Oct. 8 consistent with 280 days. None of the paper gestational wheels but all of the APPs corrected for a leap year.
Conclusion
In contrast to APPs gestational age calculators, the estimated date of confinement of the majority of paper wheels deviated from the standard pregnancy duration of 280 days. Precision in gestational age assessment is critical in a variety of clinical settings and heightened by the focus by payers and reporting agencies on elective deliveries before 39 weeks. The use of paper gestational age wheels should be abandoned.
Calculation of gestational age is a vital component of prenatal care and influences almost every decision an obstetrician makes. One of the goals of the first prenatal visit is “to estimate the gestational age of the fetus.” A normal pregnancy is considered to last 280 days. Mechanical gestational wheels from various sources are commonly used to assist in calculation of estimated date of confinement (EDC). But do all these wheels tell us the same thing? This is a question of more than academic interest.
Clinical care in a number of important areas may be negatively impacted by even small errors in assignment of gestational age. These include screening for aneuploidy and neural tube defects, decisions regarding intervention at the limits of fetal viability, the administration of corticosteroids for fetal lung maturation and of magnesium sulfate for neuroprotection, and the initiation of appropriate antepartum testing on diagnosis of postdates at 42 weeks gestation. More recently, a great deal of attention has been focused on the elimination of elective induction of labor before 39 weeks and 0 days based on a clear demonstration of increased morbidity in infants so delivered. This latter practice has become a focus for payers, public reporting agencies, and even state legislative bodies.
Against this background, we sought to compare the gestational age generated by a sample of paper gestational wheels in common use in our facility and compare them with a gestational age obtained by using the 280 day rule as a point of reference. In addition, we calculated the EDC using a variety of common electronic techniques (APPs) available for download to cell phones.
Materials and Methods
The study was undertaken after obtain a review by the institutional review board for Human Research at St. Joseph’s Hospital and Medical Center. Because the study did not involve human subjects or access to protected health information, the study was exempted from committee review and approved by the Chairman of the IRB.
This hospital is a tertiary urban academic referral center that performs over 4000 deliveries annually. For purposes of this study, we chose a last menstrual period (LMP) of Jan. 1, 2013, and calculated the EDC by using the 280 day rule. Using this standard of 280 days, a LMP of Jan. 1, 2013, gives an EDC of Oct. 8. In addition, we repeated the calculation using a LMP of Jan. 1, 2012, which was a leap year.
Over a 4-week period we approached approximately 40 attending obstetricians, obstetric, and family medicine residents, labor and delivery room nurses and third-year medical students on the obstetric service at the St. Joseph’s Hospital and Medical Center, and asked if they had a gestational wheel. Individuals were chosen at random when 1 of the authors was on the labor floor. The principle author, a board certified obstetrician-gynecologist and maternal-fetal medicine specialist, set each wheel with a LMP of Jan. 1, 2013, and recorded the EDC. The respective wheels were then photocopied, whereas set at the standard date to ensure reproducible results. We then repeated the exercise using all 20 electronic gestational age calculators (APPs) that were available for download to an iPhone on a single day in 2012. We then repeated this process using an LMP of Jan. 1, 2012, to determine whether the wheels could make accurate adjustments for a leap year.
Results
We were able to obtain 33 different mechanical gestational wheels and to access 20 electronic gestational age calculators. Details of both physical and electronic gestational age calculating devices and their accuracy are outlined in Tables 1 and 2 . The variation in estimated date of confinement demonstrated by the mechanical wheels varied from 1 to 7 days. ( Figures 1 and 2 ) Some copies of wheels from the same source gave discrepant EDCs. ( Table 1 ), In contrast, all electronic gestational age calculators yielded identical gestational ages and accurately corrected for leap year.
| Paper gestational wheel | EDC |
|---|---|
| Twin Birth Study (copy 1) | 10/05 |
| Twin Birth Study (copy 2) | 10/06 |
| Full Term FFN | 10/06 |
| HealthCheckNB | 10/06 |
| Unlabelled author | 10/07 |
| ACOG (Copy 1) | 10/07 |
| Alesse | 10/07 |
| ACOG (Copy 2) | 10/08 |
| March of Dimes | 10/08 |
| OBSTETRIX R | 10/08 |
| Matria Health Care | 10/08 |
| Air Vac | 10/08 |
| Pregnancy Superwheel | 10/08 |
| Toshiba Ultrasound | 10/08 |
| OrthTRICYCLEN (Copy 1) | 10/08 |
| Enfamil | 10/08 |
| Cefizon OB Calculator | 10/08 |
| Cord Blood Registry | 10/09 |
| Vagistat | 10/09 |
| Prenate GT | 10/09 |
| General Electric | 10/09 |
| Hill-Rom (Hillenbrand) | 10/09 |
| Greenwood Genetics Center | 10/09 |
| Birth Date Finder | 10/09 |
| Corometrics Medical Systems | 10/09 |
| Desogen | 10/09 |
| Orth Evra | 10/09 |
| Birthdate calculator | 10/09 |
| CDC | 10/10 |
| Native Air | 10/10 |
| Mirena | 10/10 |
| Orth Tri Cyclen (Copy 2) | 10/12 |
| APP wheel | EDC |
|---|---|
| Pregnancy wheel APP | 10/8 |
| http://www.duprey.net | 10/8 |
| Blue sodium corporation pregnancy wheel + | 10/8 |
| Evan Schoenberg: Perfect OB wheel | 10/8 |
| Mathias Tschopp and Pascale PFIFFNER: Medcal | 10/8 |
| Andrew Yu Preg wheel | 10/8 |
| Maritime Women’s Health Care Inc: Bioclock fertility and pregnancy calculator | 10/8 |
| The wheels SP Don Miller | 10/8 |
| Date Wheel | 10/8 |
| Residenthelper.comLLC Pregnancy | 10/8 |
| The Wheel Don Miller | 10/8 |
| Perfect IVF wheel | 10/8 |
| Health and Parenting calculator | 10/8 |
| Pregnancy: The smiles factory LTD | 10/8 |
| Baby center: My pregnancy | 10/8 |
| Pregnancy calculatory (Denoual) | 10/8 |
| Due Dater | 10/8 |
| Gestograma | 10/8 |
| Pregnancy | 10/8 |
| The Hypermunes Pregnancy Wheel | 10/8 |
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