What is a gestogram or pregnancy wheel and how is it used?

A gestogram, pregnancy wheel or gestational disk is a very useful tool used to calculate how many weeks pregnant a woman is and her expected delivery date (EDD). To do so, only the date of the last rule (FUR) must be known.

In addition, the gestogram usually provides an average of the weight and certain measurements of the developing baby, based on the calculated weeks of gestation. However, it is important to keep in mind that these are indicative data.

What is the gestogram?

A gestogram is a small wheel-shaped tool (hence also called a pregnancy wheel) pregnancy wheelo gestational disk) that allows a pregnant woman to easily calculate her current week of gestation and her expected delivery date (EDD). It is, therefore, a pregnancy calendar.

However, the most complete gestograms provide data about:

• Week of pregnancy.
• Estimated or probable date of delivery(EDD).
• Average weight of the fetus at the calculated week of gestation.
• Average fetal size at the calculated week of gestation.
• Biparietal diameter (BDP) at the calculated week of gestation.
• The length of the femur at the calculated week of gestation.
• Milestones in the baby's development for the calculated week of gestation.
• Tests or medical control at the calculated week of gestation.

What is the gestogram?

The gestogram is made up of two wheels of different sizes, made of cardboard or plastic and joined at the center. The larger wheel is marked with the different months of the year and, within each month, has stripes corresponding to each of the days.

The small wheel, which sits on top of the large wheel and can rotate on it, is marked with the different weeks of gestation, the PPF and all additional information.

The gestogram is most commonly used by the gynecologist or midwife, but the pregnant woman may also have one. In addition, there are multiple gestational discs that can be found online and in smartphone apps.

How is a gestogram used?

The pregnancy wheel or gestogram is easy to use, simply by knowing the date of onset of the last menstrual period(LMP) that the woman had before becoming pregnant.

The small wheel of the gestogram has a mark with the text"FUR","first day of last menstrual period" or equivalent. In this way, the small wheel must be turned until this mark for the FUR coincides with the corresponding date on the large wheel (which is marked with months and days).

By doing this simple step and without moving the small wheel from this position, all the marks on the small wheel (such as weeks of pregnancy, PPF, etc.) can be related to a date on the large wheel.

How a gestogram works

Thus, the woman will be able to find out her PPF, how many weeks and days pregnant she is (by looking at which week the current date corresponds to on the small wheel) and some orientative data about the baby's development according to the gestational week.

Is the gestogram reliable?

The information provided by the gestogram is reliable because the values shown on the wheel are statistical data. However, it should be kept in mind that these are approximate average values, so the fetus may not measure exactly the size indicated in the gestogram, but simply gives an approximate idea.

Likewise, it is likely that the baby will not be born exactly on the expected delivery date (EDD), but it will serve as a guide.

Thus, gestograms are very informative and are an entertaining way to obtain information related to pregnancy, but it should not be forgotten that they are indicative data and, of course, do not replace the advice and indications of the specialist who is handling the pregnancy.

FAQs from users

How should I calculate the pregnancy weeks after a frozen embryo transfer?

In pregnancies achieved with frozen embryo transfer, your gynecologist will accurately calculate the weeks of pregnancy, which may not coincide with the time elapsed since the date of your last menstruation. In this case, the specialist assigns a date of last theoretical rule.

In this way, if the cryopreservation is carried out on developmental day 5, the day of the transfer would be the 19th day of the cycle (14+5), setting the last menstrual period date 19 days before the transfer. Therefore, the weeks of pregnancy would count from this day.

On the other hand, if the embryos were 3 days old, the day of the transfer would be considered the 17th day of the cycle (14+3).
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Can a gestogram be used if the LMP is not known?

If the date of the last menstrual period or LMP is not known, the woman should wait until the first trimester ultrasound to use the gestogram. After the ultrasound, the specialist will tell the pregnant woman the LMP that corresponds to the foetal development of the baby at the time of the ultrasound.

How is the gestogram used if the gynaecologist has changed the LMP?

Depending on the ultrasound scan of the first trimester of pregnancy, the obstetrician may change the woman's last menstrual period (LMP) date, even if the pregnant woman is sure when it was. The reason for this is that ovulation does not always occur on day 14 of the menstrual cycle, so fertilisation may occur earlier or later and, therefore, the baby's development may not correspond to the indicated LMP.

In this case, the new LMP indicated by the specialist should be used in the gestogram.

Suggested for you

If you want to learn more about how you can calculate your due date, we recommend you to visit this link: What are the methods to calculate your due date?

On the other hand, if you want to know more about childbirth, you can access the following article: Childbirth: preparation, types and possible complications.