Most pregnancies last around 40 weeks, or more precisely, 38 weeks from conception. So the best way to estimate a pregnancy due date would be counting 40 weeks from the start of the last period. However, a lot of future moms have trouble estimating their pregnancy due date, mostly because they aren't entirely sure of their last period. This isn't a reason to worry because it's normal to deliver a week or two before or after the due date, but being able to calculate the exact gestational age is very important for providing better prenatal care, both in the inpatient and outpatient settings.
Although patients can do this by themselves, the providers in primary care and OB/GYN are usually those who help their patients estimate their due date. Most common way to do this is by using obstetric (OB) wheels, also known as pregnancy wheels or gestational calculators, which provide the prenatal care providers with important information.
These wheels are nothing but the small circle-shaped calendars, made of paper or plastic, that use the last menstrual period (LMP) as a starting point to help determine the due date. But, over the years, these traditional OB wheels have been slowly replaced by electronic versions made exclusively for mobile devices.
Moreover, a study published three years ago in the American Journal of Obstetrics and Gynecology claimed that electronic gestational age calculating apps for mobile devices were more accurate than commonly used paper calculating wheels, suggesting that the use of paper gestational age wheels should be abandoned.
But, with thousands of OB-Gyn related apps available for both iOS and Android devices, it's really hard to decide which one is the best and which one to use. The authors of aforementioned journal article said any electronic gestational age calculator is better than paper ones.
For this review, we decided to give OB Wheels a shot. It's a free app for iPhone and iPad devices, developed by Dr. Joshua Steinberg, a physician from NY, who's well known for making various free medical apps.
OB Wheel is the latest addition to his collection of really useful apps. It's very basic app made to resemble paper wheels, with all their options.
When you start the OB Wheels app, you'll see the home screen with three options that would help you determine estimated due date (EDD), estimated gestational age (EGA), and set the final EDD.
The first option is calendar based calculators, which allow you to put in the basic data, either last menstrual period or estimated due date, and get the estimated gestational age (in weeks). Whether you enter LMP or EDD, the other variables will be calculated automatically. You can also enter a date of a sonogram, with an option to enter Sono EGA, to make a comparison between EGA you got by calculating last menstrual period or EDD, with estimated gestational age as shown on a sonogram.
For example, you have a patient with normal pregnancy based on prenatal labs, who's unsure about her last period. According to her estimates, her LMP was on October 7, which shows that the EGA is 4 weeks and 6 days (as of today). However, the patient performed the first ultrasound a week ago, which shows a difference in sono and patient's LMP dates, with EGA of 5 weeks and 1 day. This isn't a big difference knowing that delivery week before or after is normal. But, it could be a problem if the difference between sono and LMP dates is bigger.
This is where OB Wheels app comes in handy, by allowing you to calculate all these variables in order to get the accurate EDD, and help your patient get better DD estimation and of course, better prenatal care.
The OB Wheels app also offers the option of using a traditional paper OB wheel, of course in electronic form. However, it's really hard to use its interface because of its awkward implementation. Basically, you need to pinch the screen to zoom out, to get the right size and view, but in the same time, you use the same two-finger gesture to move the wheels (both inner and outer). This requires a lot of technique and patience. While the paper wheel is neat idea it's actually pretty inconvenient to use.
Also, on the home screen, there's a part for OB/Gyn students and residents for setting schemes to reconcile the differences regarding dates (Sono and LMP).
There's a list of useful references at the bottom of the home screen, as well as disclaimer and information about the app. It should be noted that the OB Wheels app incorporates the most current ACOG guidelines and standards for dating pregnancies. There is also a list of other apps made by Dr. Joshua Steinberg, you may find useful.
OB Wheels is a simple and straightforward app, which is easy-to-use except the traditional OB wheel, which requires some re-design in order to be more functional and less complicated. Overall, OB Wheels app is a solid, free addition to a huge family of OB/Gyn related apps.
Benefit: Although the OB Wheels app is made for OB/Gyn students and providers, its simple and straightforward design makes it useful for all healthcare providers, including patients. However, patients may find calculator too complex.