Calculating the weeks of pregnancy: the obstetric slide rule and other tools to understand where we are in the pregnancy and when the baby will be born
Calculation of the weeks of pregnancy
Pregnancy does not last 9 calendar months, as we usually think, but 10 lunar monthsie 40 weeks from the beginning of the last menstruation to the most probable date of delivery; a physiological pregnancy can be concluded safely between three weeks before and two after that date (therefore between 37 and 42 weeks) and this variability of the times leads to the need to know, in every moment of pregnancy, in what period and week you are. How to make a calculation weeks of pregnancy? There are some ways to know what week you are in.
How to calculate the weeks of pregnancy?
The answer of Dr. Beatrice Brambilla of STUDIO INTRECCIO TREVIGLIO, multidisciplinary study of personal services. Facebook page -> facebook.com/studiointreccio
Calculation table of weeks of pregnancy
|First month||from the 1st day of the last menstruation up to 4 weeks + 3 days|
|Second Month||from 4 weeks + 4 days to 8 weeks + 5 days|
|Third month||from 8 weeks + 6 days to 13 weeks + 1 day|
|Fourth Month||from 13 weeks + 2 days to 17 weeks + 4 days|
|Fifth Month||from 17 weeks + 5 days to 21 weeks + 6 days|
|Sixth Month||from 22 weeks + 0 days to 26 weeks + 2 days|
|Seventh month||from 26 weeks + 3 days to 30 weeks + 4 days|
|Eighth month||from 30 weeks + 5 days to 35 weeks + 0 days|
|Ninth month||from 35 weeks + 1 day to 40 weeks + 0 days|
There is also a limit of another two weeks, by which a pregnancy can reach 42 weeks, which is taken into account when one has to be patient again if labor does not start.
1 month of pregnancy, when does it start?
The first month of pregnancy starts from day 0 and ends at 4 weeks plus three days. The first month of pregnancy begins from conception which occurs approximately 14 days after the last menstruation.
2 month of pregnancy, when does it start?
The second month of pregnancy begins at 4 weeks + 4 days and ends at 8 weeks + 5 days
3 month of pregnancy, when does it start?
The third month of pregnancy begins at weeks and 6 days and ends at 13 weeks and 1 day.
4 month of pregnancy, when does it start?
The fourth month of pregnancy begins at 13 weeks and 2 days and ends at 17 weeks and 4 days. The second trimester of pregnancy has begun.
5 month of pregnancy, when does it start?
The fifth month of pregnancy begins at 17 weeks and 5 days and ends at 21 weeks and 6 days.
6 month of pregnancy, when does it start?
The sixth month of pregnancy begins at 22 weeks and ends at 26 weeks and 2 days.
7 month of pregnancy, when does it start?
The seventh month of pregnancy starts at 26 weeks and 3 days and ends at 30 weeks and 4 days.
8 month of pregnancy, when does it start?
The eighth month of pregnancy begins at 30 weeks and 5 days and ends at exactly 35 weeks.
9 month of pregnancy, when does it start?
The ninth month of pregnancy begins at 35 weeks + 1 and ends at 40 weeks.
Weeks of pregnancy calculation obstetric rule
The Obstetrician Rule, amicably called “Ruzzola or Rotella”, is a tool used by midwives and health personnel to calculate, during pregnancy, the expected date of birth and the exact location of specific weeks of pregnancy within the months of the year, for the booking and execution of examinations, ultrasounds and blood tests.
It is important to remember that, as they are printed, they are not 100% correct but may differ by 1-2 days from each other. It is now common to find the Obstetric Rule in the kit of documents that accompany the expectant mother: many shops specializing in maternity or children’s items often give them as gifts to expectant mothers.
The obstetric slide rule is composed of two discs, one smaller and one larger, made of cardboard or plastic superimposed in the center: the outer disk shows all the days of the year, divided by month (29 February of leap years is not considered, a noteworthy element, for the midwife, if a pregnancy includes that date), while the internal one reports, declined, the weeks of pregnancy and, often, some notes related to them (beginning of the perception of fetal movements, period of increased tendency to abortion or increased risk, periods in which to carry out correctly the tests foreseen for pregnancy).
Using the ruler is possible calculate the weeks of pregnancy starting from the date of the last menstruation and then risk the day of conception. Keeping the larger disc still, the internal one is rotated until the first arrow, which reads “Date of last menstruation”, is on the day of the start of the last menstrual cycle. Once the arrow has been positioned on that date, keeping both discs still in the position obtained, you will have a clear vision of the location of the different periods and weeks of pregnancy within the solar year, so as to be facilitated in the booking of visits and exams.
There are also numerous Apps or sites that allow you to calculate how many weeks of pregnancy you are at and also give precise and useful information on the development of the fetus and the state of health of the mother.
Online pregnancy weeks calculation
On the Internet we find many tools and calculators that allow us to have a complete chart of the weeks of pregnancy. Typically it is sufficient to enter the date of the last menstruation.
On NostroFiglio.it you will find a pregnancy weeks calculator. Just enter the date of your last period and the week you are in will be automatically calculated. Link here> CALCULATOR