Gestogram: Pregnancy week (and day) calculator

Start taking folic acid three months before conceiving

What exactly is a gestogram or pregnancy calculator?

“A gestogram or pregnancy calculator is a pregnancy calendar which helps us calculate the weeks of pregnancy. The woman tells us the date of her last menstruation and, with it, we calculate how many weeks pregnant she is,” explains Dr Veronique Moens, gynaecologist at the Institut Marquès in Barcelona. So with this simple but very useful calendar, also known as the pregnancy wheel, and with the help of an ultrasound scan, your gynaecologist can check that your baby is growing correctly and that the measurements taken (femur and cranial circumference, among others) correspond to its gestational age. They also calculate the estimated due date. This is very important, because if the baby is not born after 41 weeks of pregnancy, the doctor will probably assess the possibility of inducing the birth, as the placenta has "an expiry date, and from then on it can stop working properly and not feed the baby correctly”.

It also gives you the estimated weight of your baby. If the doctor estimates that the ultrasound scan does not show a foetus that reaches the minimum parameters, they will perform a thorough examination of the placenta on the ultrasound and may carry out a Doppler to see if the foetus is receiving all the necessary nutrients through the umbilical cord.

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Why is it so important to know the number of weeks and days of a pregnancy?

“The changes that occur in the baby's development have been studied very well, so it is important to know the week we are in. It's not the same being in week 7 or 7+5 days, for example.” Natividad García, midwife

Are these pregnancy symptoms normal?

Knowing how many weeks you're pregnant isn't just going to help your doctor. You can learn how your baby is developing and whether or not the pregnancy symptoms you are experiencing are normal. If, for example, when you mark the date of your last menstrual period (or LMP), our calendar tells you that you are 16 weeks pregnant, and you are still vomiting, you should tell your doctor, since this symptom is common until the 12th week, but afterwards, although it may not be serious, it is abnormal and a symptom of a disease known as hyperemesis gravidarum.

How many weeks pregnant am I?

With this week-by-week calendar, you will know something that always causes a lot of confusion: how to count the weeks of pregnancy without error. You will also know what care you should be taking, which diagnostic tests you should have, what you should be eating, what symptoms you will experience, and so on. And the most exciting part of the gestogram and the calendar is: to pinpoint the big milestones for your baby now growing inside your womb and to see how it forms inside you week by week. You will be able to see how in 40 weeks, your child turns from a mere cell to a perfect, plump baby.

How to work out months of pregnancy from weeks

There are several ways of working out months of pregnancy from weeks, explains the expert midwife, Natividad García. The first way is to always count from the first day of the last period:

  • 1 to 4 weeks……………1st month of pregnancy
  • 5 to 8 weeks……………2nd month of pregnancy
  • 9 to 13 weeks………….3rd month of pregnancy
  • 14 to 17 weeks……….. 4th month of pregnancy
  • 18 to 22 weeks……….. 5th month of pregnancy
  • 23 to 27 weeks……….. 6th month of pregnancy
  • 28 to 31 weeks……….  7th month of pregnancy
  • 32 to 35 weeks……….  8th month of pregnancy
  • 36 to 40 weeks……….  9th month of pregnancy

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How many months are 19 weeks of pregnancy?

“According to the table above, the 19 weeks are within the 5th month of pregnancy. Another option for counting months is to count the first day of the last period as the day the month changes. So if the first day of your last period was May 20, on June 20 you will be one month pregnant, July 20 two, August 20 three and so on.” Natividad García, midwife

Why did the gynaecologist change the date of my last period?

The specialist Natividad García explains that sometimes, after carrying out the first trimester ultrasound scan, the gynaecologist will tell you that you have to change the date of our last period, even though you are absolutely certain of it. This is due to a mismatch in the development of the embryo. This is not because the baby is not developing correctly, (embryos in the first weeks of pregnancy develop in a very well-studied way) but because the development corresponds to a different week from the one we are theoretically at.

The reason is that ovulation may not have occurred on day 14 of the cycle, it may have been advanced or delayed, which also changes the time of fertilisation. The pregnancy has therefore also occurred on a different date to the one that would correspond to the date of your last period and it is necessary to change it to date the pregnancy accurately. This is very common in women with irregular cycles or cycles that are longer or shorter than usual.

If I have a cycle that is very irregular, short or long, how can I correctly calculate my weeks of pregnancy? Once the first ultrasound scan has been performed, your gynaecologist will tell you the date of your last period, which corresponds to the development of your pregnancy at that time. From this point on, any gestogram will tell you how many weeks pregnant you are.

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How can I calculate how far along I am if I don ́t know the date of my last menstrual period (LMP)?

“When we do not know the date of the last menstruation, calculation of gestational age becomes difficult. The most exact way would be through an ultrasound scan, especially if it is done in the first trimester.” Natividad García, midwife

Find out how your baby is developing

From the moment of conception until the date of birth, your body changes with one purpose: to allow a new being – your child – to form inside your uterus.

Throughout pregnancy, a number of crucial events occur for the formation of your baby. The first is undoubtedly conception. Thousands of spermatozoa have had to travel along the tortuous path of your vagina to reach the fallopian tubes where, after ovulation, the egg awaits. A few hundred will reach it and only one will be able to break through the hard skin of the egg. The second big moment is implantation, a crucial time in pregnancy when the fertilised egg is embedded in the uterine wall. If something goes wrong at that point, the pregnancy cannot continue. Until the placenta forms, the embryo will "feed" on the blood vessels that supply the endometrium, the inner layer of the uterus. After the last period, the woman's endometrium has been thickening every day throughout the menstrual cycle with this sole purpose: to host the fertilised egg.


Don ́t forget your daily folic acid supplement

All this happens within a few days of conception, as the egg divides and the organs begin to take shape. One of the first structures to form is the spinal cord. It has already formed only six weeks after the last period. In order for it to develop perfectly, without disorders such as spina bifida, the mother should have good reserves of folic acid.

Studies have shown that when the mother has low levels of vitamin B9 or folic acid, the risk of the foetus developing spinal cord problems increases. That's why today all gynaecologists and doctors recommend that women start taking supplements of this vitamin about three months before getting pregnant. In other words, it's best to start before you give up birth control.

In the first trimester, as you can see on our calendar, all the baby’s organs are formed. Some mature earlier than others. Those that take longer are the lungs, because they are no use for anything inside the mother's womb: the baby does not breathe, it receives oxygen through the placenta and the umbilical cord.

After that first trimester, the chances of the pregnancy going ahead increase considerably..

The baby’s development week by week: second trimester

The second trimester is a time of rapid growth for your baby. Now the brain, and in particular the cerebellum, will develop very quickly. The cerebellum, located at the back of the neck, is responsible for coordinating the body's movements and maintaining balance, and all motor activity, from running to writing, depends on it. Thanks to its development, your baby is now able to carry out more coordinated movements (even if you don't notice them yet).

If it’s your first pregnancy, it’s normal for you to start noticing the first movements around week 16 of the pregnancy, and a little earlier if you already have children.

Third trimester, due date is approaching

In the last three months of pregnancy, your baby has a primary mission: to prepare for birth. In this last trimester, all its organs are almost fully formed and it is mainly in charge of growing and covering itself with a thick layer of fat that will protect it. Soon it will leave the heat of your body and will pass into the much colder world. Baby is coming!

Find out your week of pregnancy accurately

Every week of your pregnancy is a wonderful mystery for you. Do you want to find out your exact week of pregnancy with our pregnancy week calculator or gestogram? The baby grows in the darkness of the uterus, at 37 degrees Celsius, protected from the outside. Its organs and senses develop and your body slowly changes. First, the fertilised egg implants in the endometrium – the lining of the uterine cavity – and it becomes an embryo. At the end of the 9th week of pregnancy it is called a foetus. A normal pregnancy lasts 40 weeks, but it can extend to 42 in some cases. With our calculator, we show you the beauty of each week of pregnancy, as well as giving you advice on the right nutrition and body care for that time.