Assessment of date of delivery of a baby

Probable date of delivery of a foetus and birth of a baby

In a woman’s life the period from puberty to menopause is child bearing stage

Women have menstruation normally at regular periodical intervals of about 25 days to 30 days.

During this period the uterus gets ready to bear a foetus and if impregnation has taken place then a baby is delivered after about nine months +.

This period is known as gestation period and is on the average 280 days

When impregnation does not take place the uterus gets ready for another cycle and sheds the lining etc. prepared to receive the fertilized egg in the form of mucous which while separating from uterus wall causes raw surface and bleeding. This will be there from 3 to 5 days and is called periods or menses
The entire process is termed as a menstrual period.

Once impregnation has taken place the uterus starts to nurture it to grow into a baby and after a full term is over expels it and the last stages are termed as labour and delivery.

How to assess when that expulsion will take place?

One commonly adopted method is to fix the date of delivery as follows

From the month and date of first day of last menstruation go back 3 months as follows

Month of last menstruation / three months back

Jan / Oct Feb/Nov March/Dec April/ Jan May/Feb June/March
July/April Aug/May Sept/June Oct/July Nov/Aug Dec/Sept.

Add or subtract 7days to the date of first day of menstruation This is an average of 15 days and delivery may take place at any time

Another is approximation of the date by the attending gynaecologist by actual examination and follow up

The following calculation is made from out of my observation and study and tested during the years 1965 to 1978 when I was in service in Tamilnadu Medical service as a Head Nurse and Nursing Superintendent. And in the last about 30 years of my retired life This is not mentioned in any standard book on O and G .to my knowledge

The period of menstrual cycle and the likely day of ovulation and becoming pregnant is fixed for every women and varies between woman

Ten months of the woman’s menstrual cycle months is the gestation period for that particular woman (Roughly ten lunar months.)

To arrive at the gestation period arrive at the number of days and hours that elapse between onset of two successive menstruation dates

Multiply this by 10. Multiplied hours are converted into days at 24 hours per day

Add this number of days to the first day of onset of the last menstruation date and arrive at the date of expected date of delivery. The delivery will take place on the date arrived at or one day earlier or late. This calculation is for a prime or first semester..

For subsequent deliveries calculate the number of days between onset of first day of last menstruation and the actual date of delivery of the first baby.

This is the gestation period of that woman for subsequent pregnancies

Just add this number of days to the date of first day of last menstruation to arrive at the date of delivery in case of second para and further pregnancies

In these days of one baby norm that most couples adopt and thanks to family planning methods there may not be any necessity to do this calculation

Serious sickness irregularity of periods due to hormonal and other causes leading to non assessibility of the individual gestation period may cause variation

Fertile period is arrived at as from 10 to 15 days from the 1str day of onset of menstruation. The actual conception day can be arrived at to within 3 days by adding 7 days to the day on which menstrual flow stops - i.e the day arrived at the day before and the day after but never after 15 days from the date of start of periods.

If the discharge stops on the 4th day then 4 plus 7 is equal to 11. Conception may take place on the 10th 11th 0r 12th day

Since as a Doctor you are in the field it is for you to observe this phenomena and come to your own decisions

K.S.Narayanaswamy
Retd. Nursing Superintendent