The date the baby should be born is often referred to as PLR = Estimated date of delivery.
On this site we have a computer to quickly calculate it by introducing the date of the last menstruation, at this link: https://www.periodofertile.it/articoli/la-data-del-parto-calcola-quando-dovbbe-nascere-il-tuo-bambino
According to the World Health Organization (WHO), the following are defined:
– pre-term pregnancies: when delivery occurs at less than 37 weeks (less than 259 days of gestation).
– full-term pregnancies: when the birth occurs between the beginning of the 37th week (37 + 0) up to the complete 41st, that is 40 + 6 (therefore from 259 to 293 days)
– pregnancies beyond the term: from the beginning of the 42nd week onwards, i.e. from 41 + 0 (from 294 days onwards).
The following table allows you to calculate with an acceptable approximation the date of delivery knowing the day of the beginning of the last menstruation.
Look in the table in the colored rows for the date of the last cycle (example 10 March) and in the row below you will find the expected date of birth (example 15 December).
Click on the image to enlarge:
Formula for calculating the date of delivery
The date of delivery is calculated taking as reference the date of the last menstruation and not the moment of conception which is assumed to occur 2 weeks later. There are therefore 280 days (40 weeks) from the date of the first day of the last menstruation with a margin of 15 days.
This method is reliable only if the expectant mother is sure of the start date of the last menstruation, if the flow was normal in reference to its usual characteristics, if the cycle did not exceed an average of 35 days in duration.
If you have used steroid contraceptives within 3 months of your last menstruation it may be that the calculation is not accurate. In any case, the first ultrasound (ultrasound for dating), which is done within the first 11 weeks, allows to date the pregnancy with a good approximation.
If you like math, you can also calculate the due date with the following formula:
- Subtract three months from the first day of your last period.
- Add seven days
- Add a year
For example, if the first day of your last period was 10/10/2020, subtract three months to get 10/7/2020. Add seven days and you will get 17/7/2020. Finally, add a year to find the estimated due date of 7/17/2021.